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On October 21, 2026, the PHP project released emergency fixes for two critical remote code execution (RCE) vulnerabilities in the PHP core runtime, tracked as CVE-2026-109618 and CVE-2026-109619 and collectively named PHP2Shell. Both are rated 9.2 (Critical) under CVSS v4.0, and both allow an unauthenticated attacker to run code on a vulnerable server. The fixed releases are PHP 8.5.12, 8.4.27, 8.3.36, and 8.2.35. Patching is the only complete fix, and you should upgrade PHP as your first priority. But patching a fleet takes time: you need to inventory where PHP runs, schedule maintenance windows and test applications against the new builds. This post shows you how to use AWS Web Application Firewall ( AWS WAF ) to help reduce exposure to the confirmed attack paths during that window. You’ll learn which request patterns to block, how to write the rules in AWS WAFv2, how to deploy them without breaking legitimate traffic and where its protection ends, so you don’t develop a false sense of safety. For how Amazon threat intelligence detected PHP2Shell exploitation before public disclosure, see Amazon Threat Intelligence identifies PHP2Shell exploitation prior to public disclosure in MadPot . For AWS service status and the AWS WAF rule that AWS recommends, see AWS Security Bulletin 2026-143-AWS . IMPORTANT: Patching is the only complete fix, and you should upgrade PHP as your first priority. The vulnerabilities in brief Both PHP2Shell vulnerabilities are unauthenticated RCE issues rooted in how PHP handles multipart/form-data request processing (the request format browsers use for file uploads) before your application code runs, which is why the AWS WAF rules in this post focus on multipart traffic, request body size, and the session upload progress field. At a high level, CVE-2026-109618 corrupts memory when PHP runs out of memory mid-request, and CVE-2026-109619 lets one request leave behind stale data that a later request on the same worker process reuses. For the root-cause analysis, affected versions, and PHP’s own guidance, see the official PHP advisories and release announcement: CVE-2026-109618 (out-of-memory corruption) – PHP advisory GHSA-w8hw-w9fx-j79w CVE-2026-109619 (stale global state) – PHP advisory GHSA-6wmf-4rv5-p3rp PHP security release announcement, October 21, 2026 Where AWS WAF fits in your response AWS WAF is a defense-in-depth control in this situation, not a replacement for the PHP upgrade. The PHP advisories are explicit: updating to a patched release is the only complete mitigation. One of the two vulnerabilities is largely outside the reach of any web application firewall, as explained later. Treat the rules in this post as mitigating controls that help reduce exposure while you patch, then remove them or keep them as supporting controls after you’ve patched. AWS WAF inspects HTTP requests at the edge. It doesn’t parse the internal structure of a multipart body, and it has no visibility into PHP worker memory or server-side configuration. The following table maps each attack element to whether AWS WAF can help mitigate it. Attack element AWS WAF coverage Session upload progress field in a multipart POST ( PHP_SESSION_UPLOAD_PROGRESS , the form field that turns on PHP’s upload-tracking feature) Yes. A targeted rule can block requests carrying that field. Multipart upload path ( multipart/form-data , the request type used for file uploads and the entry point for both vulnerabilities) Yes, if the application has no legitimate multipart uploads. Block multipart/form-data. Out-of-memory condition from an oversized body Partial. Cap the request body size. Doesn’t catch header amplification (many small part headers that cost far more memory to represent than their size on the wire) that stays under the cap. Repeated attempts against the same worker (the reused PHP process that handles many requests) Yes. A rate-based rule blunts the volume an exploit needs. fatal_error_backtraces producer (a PHP 8.5 setting that stores crash-trace state across a request) No. This is a server configuration setting ( fatal_error_backtraces=0 ). Invalid or deprecated INI diagnostics as a consumer (warnings PHP raises when applying bad configuration settings) No. This path runs server-side, not over client HTTP. Where an application does not accept multipart uploads, an edge rule that blocks multipart/form-data removes the multipart out-of-memory path that works against any application, plus the session-upload-progress trigger, which is a defense-in-depth control during the patch window. If your application does use multipart uploads, AWS WAF reduces risk but does not close the vulnerability, because header amplification (a few kilobytes of part headers that expand into far more memory inside PHP) stays within size limits and the firewall cannot parse the headers inside individual body parts. In that case, prioritize the PHP upgrade and apply the server-side mitigations described later. Implementing the AWS WAF rules The rules below are AWS WAFv2 JSON, deploy each of them on the WAF protection pack (web ACL) associated with the Amazon CloudFront distribution, Application Load Balancer, or Amazon API Gateway stage in front of your PHP workloads. IMPORTANT: Before implementing any changes, ensure that your WAFv2 logging is setup in line with AWS WAF Logging guidance. Start every rule in Count mode, confirm it does not match legitimate traffic, then switch to Block. Request body inspection limits AWS WAF inspects a bounded portion of the request body. On Application Load Balancer and AWS AppSync the limit is a fixed 8 KB. For AWS services such as CloudFront and API Gateway, the default is 16 KB and you can raise it to 32, 48, or 64 KB through the web ACL AssociationConfig as seen below. Any part of the body beyond the inspection limit counts as oversize. Choose the limit that fits the rules you deploy, because a body-size rule can only enforce a cap up to the inspected size. aws wafv2 update-web-acl ... --association-config \ 'RequestBody={CLOUDFRONT={DefaultSizeInspectionLimit=KB_16}}' AWS WAF Rule This rule targets both CVEs by blocking a request only when all three conditions in its AndStatement are true at once: The method is exactly POST – matched on the HTTP method, no transformation. A PHP session identifier is present (the nested OrStatement , so either sub-condition satisfies this leg): PHPSESSID appears as a cookie key (exact match on the key, scanning all cookies), or PHPSESSID appears anywhere in the request body (contains match). The body contains PHP_SESSION_UPLOAD_PROGRESS – the form field that activates PHP’s session upload progress feature. Pair the rule with session.upload_progress.enabled=0 on the server, which turns the feature off. { "Name": "PHP2Shell", "Priority": 0, "Statement": { "AndStatement": { "Statements": [ { "ByteMatchStatement": { "SearchString": "POST", "FieldToMatch": { "Method": {} }, "TextTransformations": [ { "Priority": 0, "Type": "NONE" } ], "PositionalConstraint": "EXACTLY" } }, { "OrStatement": { "Statements": [ { "ByteMatchStatement": { "SearchString": "PHPSESSID", "FieldToMatch": { "Cookies": { "MatchPattern": { "All": {} }, "MatchScope": "KEY", "OversizeHandling": "CONTINUE" } }, "TextTransformations": [ { "Priority": 0, "Type": "NONE" } ], "PositionalConstraint": "EXACTLY" } }, { "ByteMatchStatement": { "SearchString": "PHPSESSID", "FieldToMatch": { "Body": { "OversizeHandling": "CONTINUE" } }, "TextTransformations": [ { "Priority": 0, "Type": "NONE" } ], "PositionalConstraint": "CONTAINS" } } ] } }, { "ByteMatchStatement": { "SearchString": "PHP_SESSION_UPLOAD_PROGRESS", "FieldToMatch": { "Body": { "OversizeHandling": "CONTINUE" } }, "TextTransformations": [ { "Priority": 0, "Type": "NONE" } ], "PositionalConstraint": "CONTAINS" } } ] } }, "Action": { "Block": {} }, "VisibilityConfig": { "SampledRequestsEnabled": true, "CloudWatchMetricsEnabled": true, "MetricName": "PHP2Shell" } } Additional WAF Rules to consider Block multipart requests when the application has no uploads NOTE: This rule, if implemented in Block mode, will break applications that require file uploads. If your application does not require file uploads, then blocking multipart/form-data removes the multipart out-of-memory path that works against any application for both CVEs at the edge. A single named header is inspected in full, with no 8 KB header cap, so matching the Content-Type header is reliable. { "Name": "Block-Multipart-FormData", "Priority": 1, "Action": { "Count": {} }, "Statement": { "ByteMatchStatement": { "FieldToMatch": { "SingleHeader": { "Name": "content-type" } }, "PositionalConstraint": "CONTAINS", "SearchString": "multipart/form-data", "TextTransformations": [ { "Priority": 0, "Type": "LOWERCASE" } ] } }, "VisibilityConfig": { "SampledRequestsEnabled": true, "CloudWatchMetricsEnabled": true, "MetricName": "PHP2ShellBlockMultipart" } } Cap the request body size Capping body size reduces the out-of-memory condition behind CVE-2026-109618 and the stale state it can leave behind. Use OversizeHandling: MATCH with a size constraint so that any body larger than the threshold is blocked, including bodies that exceed the inspection limit. To enforce a cap of N bytes, the web ACL body inspection limit must be at least N. Note that you can’t cap the numeric Content-Length with a size constraint, because the constraint measures the length of the header value string, not the number it contains. If your application has legitimate large uploads, scope this rule to non-upload paths with an AndStatement on the URI path, or it will break those uploads. { "Name": "Block-Oversize-Body", "Priority": 3, "Action": { "Count": {} }, "Statement": { "SizeConstraintStatement": { "FieldToMatch": { "Body": { "OversizeHandling": "MATCH" } }, "ComparisonOperator": "GT", "Size": 8192, "TextTransformations": [ { "Priority": 0, "Type": "NONE" } ] } }, "VisibilityConfig": { "SampledRequestsEnabled": true, "CloudWatchMetricsEnabled": true, "MetricName": "PHP2ShellBlockOversizeBody" } } NOTE: if you already have the AWSManagedRulesCommonRuleSet managed rule group, the SizeRestrictions_BODY rule blocks bodies larger than 8 KB by default. If a specific managed rule breaks legitimate traffic, override that rule to Count rather than disabling the whole group. Rate-limit repeated attempts A rate-based rule on POST requests can reduce the volume an attacker can send, lowering the possibility that the vulnerabilities can be triggered by overloading the worker, while the stale-state path needs a producer request and a consumer request to land on the same worker. This rule complements a server setting of pm.max_requests=1 , which recycles the worker on each request. { "Name": "RateLimit-Posts", "Priority": 4, "Action": { "Count": {} }, "Statement": { "RateBasedStatement": { "Limit": 100, "EvaluationWindowSec": 60, "AggregateKeyType": "IP", "ScopeDownStatement": { "ByteMatchStatement": { "FieldToMatch": { "Method": {} }, "PositionalConstraint": "EXACTLY", "SearchString": "POST", "TextTransformations": [ { "Priority": 0, "Type": "NONE" } ] } } } }, "VisibilityConfig": { "SampledRequestsEnabled": true, "CloudWatchMetricsEnabled": true, "MetricName": "PHP2ShellRateLimitPosts" } } Server-side mitigations that complement AWS WAF These host and runtime changes address the parts of CVE-2026-109619 that sit below the HTTP layer a WAF inspects, so they fall outside its scope by design. Apply them alongside the AWS WAF rules as the host and runtime layer of your defense. Upgrade PHP to 8.5.12, 8.4.27, 8.3.36, or 8.2.35. This is the only complete fix. PHP 8.1 and earlier are no longer supported upstream, so check with your distribution or long-term support vendor for a backported fix, or plan a move to a supported branch. Address CVE-2026-109618 at the PHP level. Set memory_limit=-1 so applications cannot override it, and keep post_max_size low (8M where the application accepts no uploads, 32M where it does). Enforce memory bounds through container or cgroup limits, never through RLIMIT_AS or RLIMIT_DATA, which trigger the vulnerable out-of-memory path. Set fatal_error_backtraces=0 on PHP 8.5 and restart every worker. This disables the setting that stores crash-trace state across a request, one of the confirmed ways the vulnerability is triggered. Set session.upload_progress.enabled=0 and restart every worker. This turns off the upload-tracking feature that’s the other confirmed trigger, and is prudent to keep off even after patching. Prefer php.ini , FPM pool, or server startup configuration over per-request INI overrides (settings applied per request through .htaccess , php_value , or FastCGI PHP_VALUE) . Remove obsolete directives so they don’t raise diagnostic warnings. Eliminate fatal errors and execution timeouts on attacker-reachable routes, including upload, import, error-page, shutdown, serialization, and extension paths. Set pm.max_requests=1 if performance allows , so each worker process is recycled after one request, which breaks the link between the request that plants stale data and a later request that would reuse it. Turn on error logging ( log_errors=On , a working error_log , error_reporting=E_ALL ) and review your Apache, FPM, or proxy logs for repeated warnings, deprecations, fatal errors, and timeouts on attacker-controlled routes. The absence of errors is not proof of safety. Getting started Complete the following steps to get started: Inventory where PHP runs and which versions and server APIs (mod_php, FPM, FrankenPHP, LSAPI) are in use. Identify any public endpoint that accepts a request body. Decide whether each application uses multipart uploads. This determines whether you can deploy the WAF rule to block multipart requests. Create or update the web ACL in front of each PHP workload and add the applicable rules in Count mode. Raise the body inspection limit on CloudFront or API Gateway if a rule needs it. Watch the sampled requests and Amazon CloudWatch metrics for each rule. Confirm that legitimate uploads and large JSON POSTs aren’t matched. Switch the rules to Block after the metrics are clean. Order the priorities so the session upload progress and multipart rules run before the size and rate rules. Test with a benign multipart/form-data POST, an oversized body, and a request carrying PHP_SESSION_UPLOAD_PROGRESS . Expect a 403 response and the matching rule metric. In parallel, apply the PHP upgrade and the configuration mitigations. Remove or retain the AWS WAF rules as supporting controls after your fleet is patched. Conclusion The PHP2Shell vulnerabilities—CVE-2026-109618 and CVE-2026-109619—are unauthenticated RCE vulnerabilities that reach PHP before your application code runs. AWS WAF gives you a way to help narrow the attack surface during the patch window: block the session upload progress field, block multipart requests where no uploads are expected, cap request body size, and rate-limit repeated attempts. These mitigating controls can help reduce exposure, but they don’t close the vulnerabilities. Upgrade PHP to a fixed release, apply the server configuration changes, and treat the AWS WAF rules as the edge layer that supports those fixes rather than the fix itself. To learn more about the rule types used here, see the AWS WAF documentation on the web ACL body inspection limit , oversize request component handling , and handling oversize HTTP request bodies . For the vulnerability details, see the PHP advisories GHSA-w8hw-w9fx-j79w and GHSA-6wmf-4rv5-p3rp , and the PHP session upload progress manual . Alex Waddell Alex Waddell is a Principal Solutions Architect at AWS specializing in security within the Worldwide Specialist Organization, based in Scotland. Alex has been working in the security domain since 1999 and joined AWS in 2021 to work with customers across EMEA on cloud security architecture, identity, threat detection and application security. When he is not working, Alex enjoys spending time sampling rum from around the world (Alex is one of those rarely found Scottish people that doesn’t like whisky), walking his dogs in the local forest trails and traveling. Lawton Pittenger Lawton is a Worldwide Security Specialist Solutions Architect at AWS, based in New York City. He specializes in helping customers design and implement effective network security controls. At AWS, he works with customers at scale and collaborates closely with service teams to drive continuous improvement in security services based on customer needs and feedback. Outside of work, his interests include skateboarding, snowboarding, and spending time in nature. Ian Olson Ian is a Senior Security Specialist Solutions Architect at AWS. He helps customers automate security services to safeguard against threats like DDoS and web exploitations. Through intelligent automation, he delivers security solutions tailored to organizations of any scale. When he’s not working, Ian enjoys spending quality time with his two young children.

On July 19–20, 2025, various security companies and national CERTs published alerts about active exploitation of on-premise SharePoint servers. According to the reports, observed attacks did not require authentication, allowed attackers to gain full control over the infected servers, and were performed using an exploit chain of two vulnerabilities: CVE-2025-49704 and CVE-2025-49706, publicly named “ToolShell”. Additionally, on the same dates, Microsoft released out-of-band security patches for the vulnerabilities CVE-2025-53770 and CVE-2025-53771, aimed at addressing the security bypasses of previously issued fixes for CVE-2025-49704 and CVE-2025-49706. The release of the new, “proper” updates has caused confusion about exactly which vulnerabilities attackers are exploiting and whether they are using zero-day exploits. Kaspersky products proactively detected and blocked malicious activity linked to these attacks, which allowed us to gather statistics about the timeframe and spread of this campaign. Our statistics show that widespread exploitation started on July 18, 2025, and attackers targeted servers across the world in Egypt, Jordan, Russia, Vietnam, and Zambia. Entities across multiple sectors were affected: government, finance, manufacturing, forestry, and agriculture. While analyzing all artifacts related to these attacks, which were detected by our products and public information provided by external researchers, we found a dump of a POST request that was claimed to contain the malicious payload used in these attacks. After performing our own analysis, we were able to confirm that this dump indeed contained the malicious payload detected by our technologies, and that sending this single request to an affected SharePoint installation was enough to execute the malicious payload there. Our analysis of the exploit showed that it did rely on vulnerabilities fixed under CVE-2025-49704 and CVE-2025-49706, but by changing just one byte in the request, we were able to bypass those fixes. In this post, we provide detailed information about CVE-2025-49704, CVE-2025-49706, CVE-2025-53770, CVE-2025-53771, and one related vulnerability. Since the exploit code is already published online, is very easy to use, and poses a significant risk, we encourage all organizations to install the necessary updates. The exploit Our research started with an analysis of a POST request dump associated with this wave of attacks on SharePoint servers. We can see that this POST request targets the “/_layouts/15/ToolPane.aspx” endpoint and embeds two parameters: “MSOtlPn_Uri” and “MSOtlPn_DWP”. Looking at the code of ToolPane.aspx, we can see that this file itself does not contain much functionality and most of its code is located in the ToolPane class of the Microsoft.SharePoint.WebPartPages namespace in Microsoft.SharePoint.dll. Looking at this class reveals the code that works with the two parameters present in the exploit. However, accessing this endpoint under normal conditions is not possible without bypassing authentication on the attacked SharePoint server. This is where the first Microsoft SharePoint Server Spoofing Vulnerability CVE-2025-49706 comes into play. CVE-2025-49706 This vulnerability is present in the method PostAuthenticateRequestHandler, in Microsoft.SharePoint.dll. SharePoint requires Internet Information Services (IIS) to be configured in integrated mode. In this mode, the IIS and ASP.NET authentication stages are unified. As a result, the outcome of IIS authentication is not determined until the PostAuthenticateRequest stage, at which point both the ASP.NET and IIS authentication methods have been completed. Therefore, the PostAuthenticateRequestHandler method utilizes a series of flags to track potential authentication violations. A logic bug in this method enables an authentication bypass if the “Referrer” header of the HTTP request is equal to “/_layouts/SignOut.aspx”, “/_layouts/14/SignOut.aspx”, or “/_layouts/15/SignOut.aspx” using case insensitive comparison. The code displayed in the image above handles the sign-out request and is also triggered when the sign-out page is specified as the referrer. When flag6 is set to false and flag7 is set to true, both conditional branches that could potentially throw an “Unauthorized Access” exception are bypassed. On July 8, 2025, Microsoft released an update that addressed this vulnerability by introducing additional checks to detect the usage of the “ToolPane.aspx” endpoint with the sign-out page specified as the referrer. The added check uses case insensitive comparison to verify if the requested path ends with “ToolPane.aspx”. Is it possible to bypass this check, say, by using a different endpoint? Our testing has shown that this check can be easily bypassed. CVE-2025-53771 We were able to successfully bypass the patch for vulnerability CVE-2025-49706 by adding just one byte to the exploit POST request. All that was required to bypass this patch was to add a “/” (slash) to the end of the requested “ToolPane.aspx” path. On July 20, 2025, Microsoft released an update that fixed this bypass as CVE-2025-53771. This fix replaces the “ToolPane.aspx” check to instead check whether the requested path is in the list of paths allowed for use with the sign-out page specified as the referrer. This allowlist includes the following paths: “/_layouts/15/SignOut.aspx”, “/_layouts/15/1033/initstrings.js”, “/_layouts/15/init.js”, “/_layouts/15/theming.js”, “/ScriptResource.axd”, “/_layouts/15/blank.js”, “/ScriptResource.axd”, “/WebResource.axd”, “/_layouts/15/1033/styles/corev15.css”, “/_layouts/15/1033/styles/error.css”, “/_layouts/15/images/favicon.ico”, “/_layouts/15/1033/strings.js”, “/_layouts/15/core.js”, and it can contain additional paths added by the administrator. While testing the CVE-2025-49706 bypass with the July 8, 2025 updates installed on our SharePoint debugging stand, we noticed some strange behavior. Not only did the bypass of CVE-2025-49706 work, but the entire exploit chain did! But wait! Didn’t the attackers use an additional Microsoft SharePoint Remote Code Execution Vulnerability CVE-2025-49704, which was supposed to be fixed in the same update? To understand why the entire exploit chain worked in our case, let’s take a look at the vulnerability CVE-2025-49704 and how it was fixed. CVE-2025-49704 CVE-2025-49704 is an untrusted data deserialization vulnerability that exists due to improper validation of XML content. Looking at the exploit POST request, we can see that it contains two URL encoded parameters: “MSOtlPn_Uri” and “MSOtlPn_DWP”. We can see how they are handled by examining the code of the method GetPartPreviewAndPropertiesFromMarkup in Microsoft.SharePoint.dll. A quick analysis reveals that “MSOtlPn_Uri” is a page URL that might be pointing to an any file in the CONTROLTEMPLATES folder and the parameter “MSOtlPn_DWP” contains something known as WebPart markup. This markup contains special directives that can be used to execute safe controls on a server and has a format very similar to XML. While this “XML” included in the “MSOtlPn_DWP” parameter does not itself contain a vulnerability, it allows attackers to instantiate the ExcelDataSet control from Microsoft.PerformancePoint.Scorecards.Client.dll with CompressedDataTable property set to malicious payload and trigger its processing using DataTable property getter. Looking at the code of the ExcelDataSet’s DataTable property getter in Microsoft.PerformancePoint.Scorecards.Client.dll, we find the method GetObjectFromCompressedBase64String, responsible for deserialization of CompressedDataTable property contents. The data provided as Base64 string is decoded, unzipped, and passed to the BinarySerialization.Deserialize method from Microsoft.SharePoint.dll. Attackers use this method to provide a malicious DataSet whose deserialized content is shown in the image above. It contains an XML with an element of dangerous type "System.Collections.Generic.List1[[System.Data.Services.Internal.ExpandedWrapper2[...], System.Data.Services, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]", which allows attackers to execute arbitrary methods with the help of the well-known ExpandedWrapper technique aimed at exploitation of unsafe XML deserialization in applications based on the .NET framework. In fact, this shouldn’t be possible, since BinarySerialization.Deserialize in Microsoft.SharePoint.dll uses a special XmlValidator designed to protect against this technique by checking the types of all elements present in the provided XML and ensuring that they are on the list of allowed types. However, the exploit bypasses this check by placing the ExpandedWrapper object into the list. Now, to find out why the exploit worked on our SharePoint debugging stand with the July 8, 2025 updates installed, let’s take a look at how this vulnerability was fixed. In this patch, Microsoft did not really fix the vulnerability but only mitigated it by adding the new AddExcelDataSetToSafeControls class to the Microsoft.SharePoint.Upgrade namespace. This class contains new code that modifies the web.config file and marks the Microsoft.PerformancePoint.Scorecards.ExcelDataSet control as unsafe. Because SharePoint does not execute this code on its own after installing updates, the only way to achieve the security effect was to manually run a configuration upgrade using the SharePoint Products Configuration Wizard tool. Notably, the security guidance for CVE-2025-49704 does not mention the need for this step, which means at least some SharePoint administrators may skip it. Meanwhile, anyone who installed this update but did not manually perform a configuration upgrade remained vulnerable. CVE-2025-53770 On July 20, 2025, Microsoft released an update with a proper fix for the CVE-2025-49704 vulnerability. This patch introduces an updated XmlValidator that now properly validates element types in XML, preventing exploitation of this vulnerability without requiring a configuration upgrade and, more importantly, addressing the root cause and preventing exploitation of the same vulnerability through controls other than Microsoft.PerformancePoint.Scorecards.ExcelDataSet. CVE-2020-1147 Readers familiar with previous SharePoint exploits might feel that the vulnerability CVE-2025-49704/CVE-2025-53770 and the exploit used by the attackers looks very familiar and very similar to the older .NET Framework, SharePoint Server, and Visual Studio Remote Code Execution Vulnerability CVE-2020-1147. In fact, if we compare the exploit for CVE-2020-1147 and an exploit for CVE-2025-49704/CVE-2025-53770, we can see that they are almost identical. The only difference is that in the exploit for CVE-2025-49704/CVE-2025-53770, the dangerous ExpandedWrapper object is placed in the list. This makes CVE-2025-53770 an updated fix for CVE-2020-1147. Conclusions Despite the fact that patches for the ToolShell vulnerabilities are now available for deployment, we assess that this chain of exploits will continue being used by attackers for a long time. We have been observing the same situation with other notorious vulnerabilities, such as ProxyLogon, PrintNightmare, or EternalBlue. While they have been known for years, many threat actors still continue leveraging them in their attacks to compromise unpatched systems. We expect the ToolShell vulnerabilities to follow the same fate, as they can be exploited with extremely low effort and allow full control over the vulnerable server. To stay better protected against threats like ToolShell, we as a community should learn lessons from previous events in the industry related to critical vulnerabilities. Specifically, the speed of applying security patches nowadays is the most important factor when it comes to fighting such vulnerabilities. Since public exploits for these dangerous vulnerabilities appear very soon after vulnerability announcements, it is paramount to install patches as soon as possible, as a gap of even a few hours can make a critical difference. At the same time, it is important to protect enterprise networks against zero-day exploits, which can be leveraged when there is no available public patch for vulnerabilities. In this regard, it is critical to equip machines with reliable cybersecurity solutions that have proven effective in combatting ToolShell attacks before they were publicly disclosed. Kaspersky Next with its Behaviour detection component proactively protects against exploitation of these vulnerabilities. Additionally, it is able to detect exploitation and the subsequent malicious activity. Kaspersky products detect the exploits and malware used in these attacks with the following verdicts: UDS:DangerousObject.Multi.Generic PDM:Exploit.Win32.Generic PDM:Trojan.Win32.Generic HEUR:Trojan.MSIL.Agent.gen ASP.Agent.* PowerShell.Agent.*

The recently disclosed critical Microsoft SharePoint vulnerability has been under exploitation as early as July 7, 2025, according to findings from Check Point Research. The cybersecurity company said it observed first exploitation attempts targeting an unnamed major Western government, with the activity intensifying on July 18 and 19, spanning government, telecommunications, and software sectors in North America and Western Europe. Check Point also said the exploitation efforts originated from three different IP addresses – 104.238.159[.]149, 107.191.58[.]76, and 96.9.125[.]147 – one of which was previously tied to the weaponization of security flaws in Ivanti Endpoint Manager Mobile (EPMM) appliances (CVE-2025-4427 and CVE-2025-4428). "We're witnessing an urgent and active threat: a critical zero-day in SharePoint on-prem is being exploited in the wild, putting thousands of global organizations at risk," Lotem Finkelstein, Director of Threat Intelligence at Check Point Research, told The Hacker News. "Our team has confirmed dozens of compromise attempts across government, telecom, and tech sectors since July 7. We strongly urge enterprises to update their security systems immediately – this campaign is both sophisticated and fast-moving." The attack chains have been observed leveraging CVE-2025-53770, a newly patched remote code execution flaw in SharePoint Server, and chaining it with CVE-2025-49706, a spoofing vulnerability that was patched by Microsoft as part of its July 2025 Patch Tuesday update, to gain initial access and escalate privileges. It's worth mentioning at this stage that there are two sets of vulnerabilities in SharePoint that have come to light this month - CVE-2025-49704 (CVSS score: 8.8) - Microsoft SharePoint Remote Code Execution Vulnerability (Fixed on July 8, 2025) CVE-2025-49706 (CVSS score: 6.5) - Microsoft SharePoint Server Spoofing Vulnerability (Fixed on July 8, 2025) CVE-2025-53770 (CVSS score: 9.8) - Microsoft SharePoint Server Remote Code Execution Vulnerability CVE-2025-53771 (CVSS score: 6.5) - Microsoft SharePoint Server Spoofing Vulnerability CVE-2025-49704 and CVE-2025-49706, collectively referred to as ToolShell, is an exploitation chain that can lead to remote code execution on SharePoint Server instances. They were originally disclosed by Viettel Cyber Security during the Pwn2Own 2025 hacking competition earlier this May. CVE-2025-53770 and CVE-2025-53771, which became public knowledge over the weekend, have been described as variants of CVE-2025-49704 and CVE-2025-49706, respectively, indicating that they are bypasses for the original fixes put in place by Microsoft earlier this month. This is evidenced by the fact that Microsoft acknowledged active attacks exploiting "vulnerabilities partially addressed by the July Security Update." The company also noted in its advisories that the updates for CVE-2025-53770 and CVE-2025-53771 include "more robust protections" than the updates for CVE-2025-49704 and CVE-2025-49706. However, it bears noting that CVE-2025-53771 has not been flagged by Redmond as actively exploited in the wild. "CVE-2025-53770 exploits a weakness in how Microsoft SharePoint Server handles the deserialization of untrusted data," Martin Zugec, technical solutions director at Bitdefender, said. "Attackers are leveraging this flaw to gain unauthenticated remote code execution." This, in turn, is achieved by deploying malicious ASP.NET web shells that programmatically extract sensitive cryptographic keys. These stolen keys are subsequently leveraged to craft and sign malicious __VIEWSTATE payloads, thereby establishing persistent access and enabling the execution of arbitrary commands on SharePoint Server. According to Bitdefender telemetry, in-the-wild exploitation has been detected in the United States, Canada, Austria, Jordan, Mexico, Germany, South Africa, Switzerland, and the Netherlands, suggesting widespread abuse of the flaw. Palo Alto Networks Unit 42, in its own analysis of the campaign, said it observed commands being run to execute a Base64-encoded PowerShell command, which creates a file at the location "C:\PROGRA~1\COMMON~1\MICROS~1\WEBSER~1\16\TEMPLATE\LAYOUTS\spinstall0.aspx" and then parses its content. "The spinstall0.aspx file is a web shell that can execute various functions to retrieve ValidationKeys, DecryptionKeys, and the CompatabilityMode of the server, which are needed to forge ViewState Encryption keys," Unit 42 said in a threat brief. In an advisory issued Monday, SentinelOne said it first detected exploitation on July 17, with the cybersecurity company identifying three "distinct attack clusters," including state-aligned threat actors, engaging in reconnaissance and early-stage exploitation activities. Targets of the campaigns include technology consulting, manufacturing, critical infrastructure, and professional services tied to sensitive architecture and engineering organizations. "The early targets suggest that the activity was initially carefully selective, aimed at organizations with strategic value or elevated access," researchers Simon Kenin, Jim Walter, and Tom Hegel said. Analysis of the attack activity has revealed the use of a password-protected ASPX web shell ("xxx.aspx") on July 18, 2025, at 9:58 a.m. GMT. The web shell supports three functions: Authentication via an embedded form, command execution via cmd.exe, and file upload. Subsequent exploitation efforts have been found to employ the "spinstall0.aspx" web shell to extract and expose sensitive cryptographic material from the host. Spinstall0.aspx is "not a traditional command web shell but rather a reconnaissance and persistence utility," the researchers explained. "This code extracts and prints the host's MachineKey values, including the ValidationKey, DecryptionKey, and cryptographic mode settings -- information critical for attackers seeking to maintain persistent access across load-balanced SharePoint environments or to forge authentication tokens." Unlike other web shells that are typically dropped on internet-exposed servers to facilitate remote access, spinstall0.aspx appears to be designed with the sole intention of gathering cryptographic secrets that could then be used to forge authentication or session tokens across SharePoint instances. These attacks, per CrowdStrike, commence with a specially crafted HTTP POST request to an accessible SharePoint server via the "/_layouts/15/ToolPane.aspx" endpoint that attempts to write spinstall0.aspx via PowerShell. The company said it blocked hundreds of exploitation attempts across more than 160 customer environments. SentinelOne also discovered a cluster dubbed "no shell" that took a "more advanced and stealthy approach" to other threat actors by opting for in-memory .NET module execution without dropping any payloads on disk. The activity originated from the IP address 96.9.125[.]147. "This approach significantly complicates detection and forensic recovery, underscoring the threat posed by fileless post-exploitation techniques," the company said, positing that it's either a "skilled red team emulation exercise or the work of a capable threat actor with a focus on evasive access and credential harvesting." It's currently not known who is behind the attack activity, although Google-owned Mandiant has attributed the early-exploitation to a China-aligned hacking group. Data from Censys shows that there are 9,762 on-premises SharePoint servers online, although it's currently not known if all of them are susceptible to the flaws. Given that SharePoint servers are a lucrative target for threat actors due to the nature of sensitive organizational data stored in them, it's essential that users move quickly to apply the fixes, rotate the keys, and restart the instances. "We assess that at least one of the actors responsible for the early exploitation is a China-nexus threat actor," Charles Carmakal, CTO, Mandiant Consulting at Google Cloud, said in a post on LinkedIn. "We're aware of victims in several sectors and global geographies. The activity primarily involved the theft of machine key material which could be used to access victim environments after the patch has been applied." (The story was updated after publication on July 23, 2025, to reflect the change in CVSS scores.)

Check Point Research (CPR) conducted a focused analysis of Storm-2603, a threat actor associated with recent ToolShell exploitations, together with other Chinese APT groups. Storm-2603 utilizes a custom malware Command and Control (C2) framework dubbed internally by the attacker as “ak47c2”. This framework includes at least two different types of clients: HTTP-based (dubbed by us “ak47http”) and DNS-based (dubbed by us “ak47dns”). Based on VirusTotal data, Storm-2603 likely targeted some organizations in Latin America throughout the first half of 2025, in parallel to attacking organizations in APAC. Some of the actor’s TTPs align with many other ransomware groups, and involve open-source tools such as PsExec and masscan. In addition, the threat actors use a custom tool that leverages the BYOVD (Bring Your Own Vulnerable Driver) technique to tamper with endpoint protections. Storm-2603 attacks involved multiple ransomware families, sometimes bundled together. Those are commonly deployed by abusing DLL hijacking. Check Point Research (CPR) has been closely monitoring the ongoing exploitation of a group of Microsoft SharePoint Server vulnerabilities collectively referred to as “ToolShell.” These active attacks leverage four vulnerabilities—CVE-2025-49704, CVE-2025-49706, CVE-2025-53770, and CVE-2025-53771—and are attributed to multiple China affiliated threat actors. Among the threat groups identified by Microsoft, two are known APTs: Linen Typhoon (aka APT27) and Violet Typhoon (aka APT31). Another group is a newly observed, previously undocumented cluster called Storm-2603. While Microsoft linked this cluster’s activity to potential ransomware deployment, it was unable to assess the group’s objectives. As part of our ongoing investigation into ToolShell and its associated risks, we launched a targeted effort to better understand and characterize the threat posed by Storm-2603. Throughout our analysis, we uncovered several files likely tied to Storm-2603 intrusions, offering new insights that correspond to Microsoft’s description of the group. In this publication, we provide an in-depth examination of Storm-2603’s tactics, techniques, and procedures (TTPs), along with a technical breakdown of the ak47c2, a custom malware framework used in their attacks and their different ransomware payloads. Storm-2603 was first mentioned by Microsoft during investigations into a set of attacks on Microsoft SharePoint servers, known as the “ToolShell” campaign. While some activity was tied to known Chinese affiliated groups like Linen Typhoon (APT27) and Violet Typhoon (APT31), Storm-2603 appeared as a new, previously unreported actor. Microsoft linked the group to Lockbit and Warlock ransomware use. Figure 1 – Events associated with Storm-2603. Microsoft’s report provided only limited information about Storm-2603, including some of the TTPs associated with it, most of them quite generic. In addition, some of the reported indicators of compromise (IOCs) helped us uncover additional artifacts associated with previous Storm-2603 intrusions. One domain in particular, update.updatemicfosoft[.]com, linked to Storm-2603’s SharePoint exploitation, turned out to have been used in earlier campaigns dating back to March 2025. In those operations, it served as a C2 server for both DNS tunneling malware and an HTTP backdoor and was part of infrastructure used to deliver LockBit Black and Warlock/x2anylock ransomware. Our search for cases where the IOCs reported by Microsoft, revealed two incidents in which LockBit Black and WarLock ransomware variants were deployed together, in addition to multiple other tools, mostly open-source. In April 2025, a RAR archive named Evidencia.rar was uploaded to VirusTotal. The archive contains several artifacts likely extracted from compromised machines in a Storm-2603 case in a LATAM country. The artifacts in the archive provide a look at some of the open-source tools used by the actors in the intrusions which correlates with previous knowledge of the group: WinPcap – Captures and filters network traffic on Windows. PsExec – Executes commands on remote Windows systems. SharpHostInfo – Collects host and domain info on Windows environments. nxc – Exploits common vulnerabilities in network services. In addition to the open-source tools, the archive also contains the custom backdoor used by the group, as well as its unique ransomware payloads. dnsclient.exe – A custom backdoor utilized by Storm-2603 that communicates over DNS tunneling with update.updatemicfosoft[.]com, a domain associated with the group. See the next section for our analysis of the backdoor. 7z.exe & 7z.dll – Legitimate 7z executable side-loading malicious 7z.dll delivering X2anylock (aka Warlock), a ransomware used by Storm-2603. bbb.msi – An installer which uses clink_x86.exe to side-load clink_dll_x86.dll, leading to the execution of LockBit Black ransomware. Another MSI file uploaded to VirusTotal in April used a similar deployment method, starting with the MSI installer to launch multiple ransomware strains simultaneously: Figure 2 – MSI Multi-Ransomware Deployment. The MSI relies on the following files: MpCmdRun.exe & Mpclient.dll – Warlock Ransomware, deployed via DLL-hijacking. clink_x86.exe & clink_dll_x86.dll – LockBit Black ransomware, deployed via DLL-hijacking. z.exe & z.dll – x2anylock ransomware, deployed via DLL-hijacking. VMToolsEng.exe – Custom Antivirus Terminator. ServiceMouse.sys – Vulnerable driver used by VMToolsEng.exe for killing Antivirus processes. log.exe – A list of Antivirus processes to kill. msi.bat – Executes VMToolsEng.exe. 1.bat – Executes all the needed executables and the MSI. We attributed two custom backdoors to Storm-2306, both of which appear to be part of the framework named AK47 C2 based on the shared PDB path: C:\Users\Administrator\Desktop\work\tools\ak47c2\. When executed, the program immediately hides its console window, determines the host computer name (defaulting to unknown.local if that fails), and builds a DNS‑based command‑and‑control payload. It chooses a random five-character session ID, such as H4T14, and prefixes it with 1 for task requests or 2 for result uploads (e.g., 1H4T14 or 2H4T14). Each element, such as the task/result tag, a size flag (a for “all” when the entire message fits into one request), and the computer name, is XOR‑encoded with the ASCII key “VHBD@H”, converted to hexadecimal, and concatenated with dots before being prepended to the C2 domain update.micfosoft[.]com. This what the overall query looks like: DNS TXT and MG (a mail group member record type) record lookups (DnsQuery_A) are used to transmit and retrieve data. If the C2 server is unreachable, the client simply receives error 9003 (DNS_ERROR_RCODE_NAME_ERROR). Otherwise, the response text is decoded from hex, XOR‑decrypted, and parsed for the delimiter “:::”, which separates metadata from the actual command string. Commands run under cmd.exe /c 2>&1; a built‑in directive sleep n pauses execution for n seconds. For outputs larger than 0xFF bytes, the backdoor fragments data into 63‑byte sub‑segments. Each DNS query then follows: HttpClient backdoor has the pdb path C:\Users\Administrator\Desktop\work\tools\ak47c2\httpclient-cpp\x64\Release\httpclient-cpp.pdb and uses plain HTTP instead of DNS for the C2. It is built as a 64‑bit console program that also immediately hides its window on launch. On start‑up, the malware gathers the host computer name (similar to the DNS version, it defaults to unknown.local), then builds a JSON object with the fields cmd, cmd_id, fqdn, result, and type. For a task request, the object looks like this: {"cmd":"","cmd_id":"","fqdn":" ","result":"","type":"task"} After the host executes a command, the result is sent back with type:”result”. Before transmission, the entire JSON blob is XOR‑encrypted with the ASCII key “VHBD@H”, converted to hexadecimal, and placed in the body of an HTTP POST to “/” with generic headers (Content‑Type: text/plain, Accept: */*). The C2 replies with a similarly encoded JSON where the cmd field contains the next command. The implant executes it via cmd.exe /c 2>&1 and returns the output. We identified that during these attacks, several types of ransomware were deployed simultaneously. One is regular LockBit Black, and the second uses the.x2anylock extension. This extension was later used by the Warlock ransomware operator, mentioned in Microsoft’s report on the SharePoint exploitation. The Warlock ransom note is usually saved as How to decrypt my data.txt and looks like this: Figure 3 – Warlock Group ransom note. The ransom notes for all ransomware strains deployed by Storm-2603 are named How to decrypt my data.log (x2anylock) or .README.txt (LockBit Black) and have the same short content: Your decrypt ID: [redacted] Tox ID Support: 3DCE[redacted] Email Support: [redacted]@proton.me,[redacted]@proton.me,[redacted]@proton.me You can contact us in email or qtox. This ransom note’s name How to decrypt my data.log appeared in a recent LinkedIn post by Huntress, describing the case where multiple ransomware families were deployed together against the same target. While not a new tactic, this approach is rarely observed among established ransomware groups. An important part of the infection package described earlier is called Antivirus Terminator. It is a custom command line tool abusing a third-party signed legitimate driver to kill processes. From what we can see, it’s been in the wild since at least late 2024. The tool requires administrative privileges on the infected machine. The screenshot below shows how the listing is displayed in the console when the tool is run without parameters: Figure 4 – Antivirus Terminator supported arguments when run without parameters. The tool first creates a service called ServiceMouse, where the path to the service binary file is ServiceMouse.sys from the package. Next, the tool communicates with the installed service via IO control code 0x99000050, which is responsible for killing processes. The tool also has more capabilities, like deleting files and uninstalling drivers, and these use different IO control codes (0x990000D0 and 0x990001D0). Figure 6 – Antivirus Terminator kills process using third-party driver. The supplied third-party driver is a legitimate and signed component of Antiy System In-Depth Analysis Toolkit, originally named AToolsKrnl64.sys. The toolkit was developed by Antiy Labs, a Chinese security vendor, and features a graphical user interface that allows users, among others, to interact with and manipulate processes. The ability to kill processes is the most important feature which is abused by threat actors in this particular case. Figure 7 – Antiy System In-Depth Analysis Tookit GUI. The following piece of code in the driver handles the IO control code 0x99000050 mentioned above: Figure 8 – IO control code processing in the Antiy driver. The second function is the piece of code responsible for killing a process with a given PID. In this report we analyze Storm-2603, a relatively new threat actor first mentioned by Microsoft during investigations into the “ToolShell” campaign targeting SharePoint servers. While some of the exploitation activity was tied to known Chinese APT groups, Storm-2603 stood out as a previously undocumented group linked to ransomware deployment. By examining infrastructure indicators shared in public reporting, we were able to connect this actor to earlier campaigns involving LockBit Black and Warlock/X2anylock ransomware, dating back to at least March 2025. These earlier attacks used similar infrastructure and tools, including DNS tunneling and HTTP-based backdoors. Interestingly, multiple ransomware variants were deployed in the same attack. This behavior, along with the overlap in techniques, helps us better understand how Storm-2603 operates “The Turkish Rat” Evolved Adwind in a Massive Ongoing Phishing Campaign Check Point Research Publications August 11, 2017 “The Next WannaCry” Vulnerability is Here Check Point Research Publications March 12, 2026 “Handala Hack” – Unveiling Group’s Modus Operandi SUBSCRIBE TO CYBER INTELLIGENCE REPORTS We value your privacy! BFSI uses cookies on this site. We use cookies to enable faster and easier experience for you. By continuing to visit this website you agree to our use of cookies.

The US government has warned businesses and critical infrastructure organizations to stay vigilant against wide-ranging attacks from the Interlock ransomware gang. The joint advisory from four government agencies including the FBI and the Department of Health and Human Services (HHS), highlighted the novel initial access techniques used by the cybercrime group. This includes “drive-by-download” and ClickFix social engineering techniques. The group, first identified in late September 2024, has been observed targeting various business, critical infrastructure and other organizations in North America and Europe. High-profile incidents attributed to Interlock in 2025 include Kettering Health, a major healthcare provider in western Ohio, US, and Scottish local authority West Lothian council. Its favored tactic is double extortion, in which threat actors exfiltrate data as well as encrypt it, increasing the pressure on victims to pay a ransom demand. The ransomware encryptors deployed are designed for both Windows and Linux operating systems. “These actors are opportunistic and financially motivated in nature and employ tactics to infiltrate and disrupt the victim’s ability to provide their essential services,” the advisory, published on July 22, warned. “Uncommon” Method for Initial Access The FBI has observed Interlock using a technique called drive-by-download to obtain initial access, which was described as an “uncommon method among ransomware groups.” This technique involves the compromise of legitimate websites, which automatically installs malware onto the victim’s device upon being visited. Interlock actors have also used the ClickFix social engineering technique to gain initial access. This tactic involves the use of a fake error or verification message to manipulate victims into copying and pasting a malicious script and then running it. Post-compromise, affiliates deploy various methods for discovery, credential access and lateral movement. A PowerShell script executes a series of commands designed to gather information on victim machines. Once command and control (C2) is established, a series of PowerShell commands are used to download a credential stealer and keylogger binary. These tools collect various information to help facilitate access between systems, including login information and users’ keystrokes. Remote desktop protocol (RDP) is also leveraged to facilitate lateral movement. Data is then exfiltrated via AzCopy, a legitimate tool used to copy files, and various file transfer tools, including WinSCP. Following exfiltration, Interlock launches ransomware encryptors. Encrypted files are appended with a ransom note titled !README!.txt. Interlock affiliates do not leave an initial ransom demand or payment instructions in this note, instead each victim is provided with a unique code and instructions to contact the ransomware actors via a .onion URL. When contact is made, victims are instructed to make ransom payments in Bitcoin to cryptocurrency wallet addresses provided by the actors. The actors also threaten to publish the victim’s exfiltrated data to their leak site on the Tor network unless the victim pays the ransom demand. “The actors have previously followed through on this threat,” the agencies noted. How to Defend Against Interlock Attacks The advisory set out a range of recommendations for organizations to protect against the techniques used by Interlock. These include: Reduce the risk of drive-by-download by implementing domain name system (DNS) to block users from accessing malicious sites Implement web access firewalls to mitigate and prevent unknown commands or process injection from malicious domains or websites Implement additional email security measures, including disabling hyperlinks in received emails Require all accounts with passwords to comply with National Institute of Standards and Technology (NIST) password guidance and implement multi-factor authentication (MFA) for all services Filter network traffic by preventing unknown or untrusted origins from accessing remote services on internal systems Maintain and retain multiple copies of sensitive or proprietary data and servers in a physically separate, segmented and secure location Segment networks to prevent the spread of ransomware

On July 19–20, 2025, various security companies and national CERTs published alerts about active exploitation of on-premise SharePoint servers. According to the reports, observed attacks did not require authentication, allowed attackers to gain full control over the infected servers, and were performed using an exploit chain of two vulnerabilities: CVE-2025-49704 and CVE-2025-49706, publicly named “ToolShell”. Additionally, on the same dates, Microsoft released out-of-band security patches for the vulnerabilities CVE-2025-53770 and CVE-2025-53771, aimed at addressing the security bypasses of previously issued fixes for CVE-2025-49704 and CVE-2025-49706. The release of the new, “proper” updates has caused confusion about exactly which vulnerabilities attackers are exploiting and whether they are using zero-day exploits. Kaspersky products proactively detected and blocked malicious activity linked to these attacks, which allowed us to gather statistics about the timeframe and spread of this campaign. Our statistics show that widespread exploitation started on July 18, 2025, and attackers targeted servers across the world in Egypt, Jordan, Russia, Vietnam, and Zambia. Entities across multiple sectors were affected: government, finance, manufacturing, forestry, and agriculture. While analyzing all artifacts related to these attacks, which were detected by our products and public information provided by external researchers, we found a dump of a POST request that was claimed to contain the malicious payload used in these attacks. After performing our own analysis, we were able to confirm that this dump indeed contained the malicious payload detected by our technologies, and that sending this single request to an affected SharePoint installation was enough to execute the malicious payload there. Our analysis of the exploit showed that it did rely on vulnerabilities fixed under CVE-2025-49704 and CVE-2025-49706, but by changing just one byte in the request, we were able to bypass those fixes. In this post, we provide detailed information about CVE-2025-49704, CVE-2025-49706, CVE-2025-53770, CVE-2025-53771, and one related vulnerability. Since the exploit code is already published online, is very easy to use, and poses a significant risk, we encourage all organizations to install the necessary updates. The exploit Our research started with an analysis of a POST request dump associated with this wave of attacks on SharePoint servers. We can see that this POST request targets the “/_layouts/15/ToolPane.aspx” endpoint and embeds two parameters: “MSOtlPn_Uri” and “MSOtlPn_DWP”. Looking at the code of ToolPane.aspx, we can see that this file itself does not contain much functionality and most of its code is located in the ToolPane class of the Microsoft.SharePoint.WebPartPages namespace in Microsoft.SharePoint.dll. Looking at this class reveals the code that works with the two parameters present in the exploit. However, accessing this endpoint under normal conditions is not possible without bypassing authentication on the attacked SharePoint server. This is where the first Microsoft SharePoint Server Spoofing Vulnerability CVE-2025-49706 comes into play. CVE-2025-49706 This vulnerability is present in the method PostAuthenticateRequestHandler, in Microsoft.SharePoint.dll. SharePoint requires Internet Information Services (IIS) to be configured in integrated mode. In this mode, the IIS and ASP.NET authentication stages are unified. As a result, the outcome of IIS authentication is not determined until the PostAuthenticateRequest stage, at which point both the ASP.NET and IIS authentication methods have been completed. Therefore, the PostAuthenticateRequestHandler method utilizes a series of flags to track potential authentication violations. A logic bug in this method enables an authentication bypass if the “Referrer” header of the HTTP request is equal to “/_layouts/SignOut.aspx”, “/_layouts/14/SignOut.aspx”, or “/_layouts/15/SignOut.aspx” using case insensitive comparison. The code displayed in the image above handles the sign-out request and is also triggered when the sign-out page is specified as the referrer. When flag6 is set to false and flag7 is set to true, both conditional branches that could potentially throw an “Unauthorized Access” exception are bypassed. On July 8, 2025, Microsoft released an update that addressed this vulnerability by introducing additional checks to detect the usage of the “ToolPane.aspx” endpoint with the sign-out page specified as the referrer. The added check uses case insensitive comparison to verify if the requested path ends with “ToolPane.aspx”. Is it possible to bypass this check, say, by using a different endpoint? Our testing has shown that this check can be easily bypassed. CVE-2025-53771 We were able to successfully bypass the patch for vulnerability CVE-2025-49706 by adding just one byte to the exploit POST request. All that was required to bypass this patch was to add a “/” (slash) to the end of the requested “ToolPane.aspx” path. On July 20, 2025, Microsoft released an update that fixed this bypass as CVE-2025-53771. This fix replaces the “ToolPane.aspx” check to instead check whether the requested path is in the list of paths allowed for use with the sign-out page specified as the referrer. This allowlist includes the following paths: “/_layouts/15/SignOut.aspx”, “/_layouts/15/1033/initstrings.js”, “/_layouts/15/init.js”, “/_layouts/15/theming.js”, “/ScriptResource.axd”, “/_layouts/15/blank.js”, “/ScriptResource.axd”, “/WebResource.axd”, “/_layouts/15/1033/styles/corev15.css”, “/_layouts/15/1033/styles/error.css”, “/_layouts/15/images/favicon.ico”, “/_layouts/15/1033/strings.js”, “/_layouts/15/core.js”, and it can contain additional paths added by the administrator. While testing the CVE-2025-49706 bypass with the July 8, 2025 updates installed on our SharePoint debugging stand, we noticed some strange behavior. Not only did the bypass of CVE-2025-49706 work, but the entire exploit chain did! But wait! Didn’t the attackers use an additional Microsoft SharePoint Remote Code Execution Vulnerability CVE-2025-49704, which was supposed to be fixed in the same update? To understand why the entire exploit chain worked in our case, let’s take a look at the vulnerability CVE-2025-49704 and how it was fixed. CVE-2025-49704 CVE-2025-49704 is an untrusted data deserialization vulnerability that exists due to improper validation of XML content. Looking at the exploit POST request, we can see that it contains two URL encoded parameters: “MSOtlPn_Uri” and “MSOtlPn_DWP”. We can see how they are handled by examining the code of the method GetPartPreviewAndPropertiesFromMarkup in Microsoft.SharePoint.dll. A quick analysis reveals that “MSOtlPn_Uri” is a page URL that might be pointing to an any file in the CONTROLTEMPLATES folder and the parameter “MSOtlPn_DWP” contains something known as WebPart markup. This markup contains special directives that can be used to execute safe controls on a server and has a format very similar to XML. While this “XML” included in the “MSOtlPn_DWP” parameter does not itself contain a vulnerability, it allows attackers to instantiate the ExcelDataSet control from Microsoft.PerformancePoint.Scorecards.Client.dll with CompressedDataTable property set to malicious payload and trigger its processing using DataTable property getter. Looking at the code of the ExcelDataSet’s DataTable property getter in Microsoft.PerformancePoint.Scorecards.Client.dll, we find the method GetObjectFromCompressedBase64String, responsible for deserialization of CompressedDataTable property contents. The data provided as Base64 string is decoded, unzipped, and passed to the BinarySerialization.Deserialize method from Microsoft.SharePoint.dll. Attackers use this method to provide a malicious DataSet whose deserialized content is shown in the image above. It contains an XML with an element of dangerous type "System.Collections.Generic.List1[[System.Data.Services.Internal.ExpandedWrapper2[...], System.Data.Services, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]", which allows attackers to execute arbitrary methods with the help of the well-known ExpandedWrapper technique aimed at exploitation of unsafe XML deserialization in applications based on the .NET framework. In fact, this shouldn’t be possible, since BinarySerialization.Deserialize in Microsoft.SharePoint.dll uses a special XmlValidator designed to protect against this technique by checking the types of all elements present in the provided XML and ensuring that they are on the list of allowed types. However, the exploit bypasses this check by placing the ExpandedWrapper object into the list. Now, to find out why the exploit worked on our SharePoint debugging stand with the July 8, 2025 updates installed, let’s take a look at how this vulnerability was fixed. In this patch, Microsoft did not really fix the vulnerability but only mitigated it by adding the new AddExcelDataSetToSafeControls class to the Microsoft.SharePoint.Upgrade namespace. This class contains new code that modifies the web.config file and marks the Microsoft.PerformancePoint.Scorecards.ExcelDataSet control as unsafe. Because SharePoint does not execute this code on its own after installing updates, the only way to achieve the security effect was to manually run a configuration upgrade using the SharePoint Products Configuration Wizard tool. Notably, the security guidance for CVE-2025-49704 does not mention the need for this step, which means at least some SharePoint administrators may skip it. Meanwhile, anyone who installed this update but did not manually perform a configuration upgrade remained vulnerable. CVE-2025-53770 On July 20, 2025, Microsoft released an update with a proper fix for the CVE-2025-49704 vulnerability. This patch introduces an updated XmlValidator that now properly validates element types in XML, preventing exploitation of this vulnerability without requiring a configuration upgrade and, more importantly, addressing the root cause and preventing exploitation of the same vulnerability through controls other than Microsoft.PerformancePoint.Scorecards.ExcelDataSet. CVE-2020-1147 Readers familiar with previous SharePoint exploits might feel that the vulnerability CVE-2025-49704/CVE-2025-53770 and the exploit used by the attackers looks very familiar and very similar to the older .NET Framework, SharePoint Server, and Visual Studio Remote Code Execution Vulnerability CVE-2020-1147. In fact, if we compare the exploit for CVE-2020-1147 and an exploit for CVE-2025-49704/CVE-2025-53770, we can see that they are almost identical. The only difference is that in the exploit for CVE-2025-49704/CVE-2025-53770, the dangerous ExpandedWrapper object is placed in the list. This makes CVE-2025-53770 an updated fix for CVE-2020-1147. Conclusions Despite the fact that patches for the ToolShell vulnerabilities are now available for deployment, we assess that this chain of exploits will continue being used by attackers for a long time. We have been observing the same situation with other notorious vulnerabilities, such as ProxyLogon, PrintNightmare, or EternalBlue. While they have been known for years, many threat actors still continue leveraging them in their attacks to compromise unpatched systems. We expect the ToolShell vulnerabilities to follow the same fate, as they can be exploited with extremely low effort and allow full control over the vulnerable server. To stay better protected against threats like ToolShell, we as a community should learn lessons from previous events in the industry related to critical vulnerabilities. Specifically, the speed of applying security patches nowadays is the most important factor when it comes to fighting such vulnerabilities. Since public exploits for these dangerous vulnerabilities appear very soon after vulnerability announcements, it is paramount to install patches as soon as possible, as a gap of even a few hours can make a critical difference. At the same time, it is important to protect enterprise networks against zero-day exploits, which can be leveraged when there is no available public patch for vulnerabilities. In this regard, it is critical to equip machines with reliable cybersecurity solutions that have proven effective in combatting ToolShell attacks before they were publicly disclosed. Kaspersky Next with its Behaviour detection component proactively protects against exploitation of these vulnerabilities. Additionally, it is able to detect exploitation and the subsequent malicious activity. Kaspersky products detect the exploits and malware used in these attacks with the following verdicts: UDS:DangerousObject.Multi.Generic PDM:Exploit.Win32.Generic PDM:Trojan.Win32.Generic HEUR:Trojan.MSIL.Agent.gen ASP.Agent.* PowerShell.Agent.*