CVE-2026-85656 - OS command injection in Amazon log4j-cve-2021-44228-hotpatch

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.

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) on Friday added two security flaws impacting Microsoft SharePoint and Mikrotik RouterOS to its Known Exploited Vulnerabilities (KEV) catalog, citing evidence of active exploitation. The vulnerabilities in question are as follows - CVE-2026-65660 (CVSS score: 8.8) - A code injection vulnerability in Microsoft Office SharePoint that allows an authorized attacker to execute code over a network. CVE-2026-67279 (CVSS score: 6.9) - An improper enforcement of behavioral workflow vulnerability in Mikrotik RouterOS that could allow an unauthenticated client to open a session channel and send an exec request. As reported by The Hacker News earlier this week, CVE-2026-65660 was originally described by Microsoft as a spoofing vulnerability impacting SharePoint Server. The tech giant has since updated the advisory to state that it could be abused to obtain remote code execution. "As of 9/25/2026, Microsoft had reliable evidence of observed attacks against exploitation of this vulnerability," the Windows maker noted. Microsoft hasn't disclosed who was behind the exploitation efforts, when they started, how many organizations have been targeted, how many of them have been successful, and what attackers did once inside the vulnerable service. The second vulnerability to be added to the KEV catalog is CVE-2026-67279, which has been chained along with CVE-2026-86060, an argument injection flaw in the RouterOS login process, as part of an exploit codenamed MikroTrick. The exploit chain has been employed to take full administrative control of internet-exposed susceptible routers without the need for a password, per CERT Polska. "Combining the two vulnerabilities resulted in full unauthenticated access to the administrative console," the Polish cybersecurity agency said. "CVE-2026-67279 allowed an unauthenticated client to create a session channel, while CVE-2026-86060 allowed it to supply login with an attacker-controlled policy mask." In a separate analysis, Bishop Fox said it was able to reproduce the complete administrative takeover on vulnerable RouterOS 7.x builds. "MikroTrick combines two failures at different trust boundaries," security researcher Emilio Gallegos said. "The first allows an unauthenticated connection to reach functionality that RouterOS should expose only after login. The second causes the login process to treat data from that connection as a trusted administrative identity." "MikroTrick exposes a design risk in privileged software: a feature intended only for trusted local callers becomes a remote attack surface when an upstream component loses track of authentication state." It's worth noting that CISA added CVE-2026-86060 to its KEV catalog on September 11, 2026. Federal Civilian Executive Branch (FCEB) agencies have time until September 28, 2026, to apply the necessary fixes.

Attackers are exploiting a new critical zero-day flaw in Cisco Catalyst SD-WAN Manager, the system companies use to manage their Cisco SD-WAN networks, Cisco said in an advisory on September 30. The flaw, CVE-2026-76504, could allow a remote attacker with no login access to use the Manager's API as the admin user. Fixed releases are available, and there is no workaround. It carries a CVSS score of 9.8 out of 10. It sits in the part of the Manager's API that handles login sessions. The Manager mishandles URI encoding in an HTTP request. A crafted request can therefore bypass an authentication rule intended to restrict access to a single API endpoint. The attacker needs no credentials, only the ability to send that request to the Manager's API. Managers exposed to the internet are at risk of compromise, according to Cisco. By default, the admin user holds the netadmin role, which is allowed to perform all operations on the device. Cisco said its Product Security Incident Response Team "became aware of active exploitation of this vulnerability" in September 2026. The flaw was found while Cisco's Technical Assistance Center (TAC) was handling a support case. The advisory does not say how many customers were attacked, when the attacks began, who carried them out, or what the attackers did with the access. Who Needs to Upgrade The flaw affects SD-WAN Manager regardless of how the system is configured. No other product is listed as affected. These are the first fixed releases for each release train: CVE-2026-76504 is separate from three Cisco SD-WAN flaws fixed earlier: CVE-2026-20182 in May, and CVE-2026-20245 and CVE-2026-20262 in June. A comparison of the advisories shows that the fixed releases for those flaws are all older than the ones in the table above. So a Manager last upgraded for the May or June fixes still needs this update. The table does not list the 20.10, 20.11, 20.13, 20.14, or 20.16 release trains, which Cisco's May advisory did list. The advisory also does not name Cisco SD-WAN Cloud-Pro or Cisco SD-WAN for Government (FedRAMP), two deployment types named in the May and June advisories. Cisco SD-WAN Cloud (Cisco Managed) is already fixed in release 20.15.605, and customers on it need to take no action. Until an on-prem Manager is upgraded, Cisco advises restricting access to it from unsecured networks such as the internet. Where internet access is required, only known, trusted hosts should be allowed in, and the control components should sit behind a firewall. Cisco Catalyst SD-WAN Cloud Hosted environments already have this mitigation in place. The mitigation worked in a test environment, according to Cisco, which advises customers to assess its impact on their own networks before applying it. Cisco's SD-WAN hardening guide says administrative interfaces, such as ports 443, 22 and 830, should not be exposed directly to the internet. HTTPS access to the Manager should come only from a jump host or a management subnet. Checking for Signs of Compromise The signs of compromise Cisco describes involve j_security_check, the request path the Manager uses for session-based logins. In Cisco's example, one character of that path is URI-encoded, giving /%6a_security_check, where %6a stands for the letter j. Two log files are the places to look for j_security_check entries from unknown or unauthorized IP addresses: File: /var/log/nms/containers/service-proxy/serviceproxy-access.log File: /var/log/nms/vmanage-server.log, in particular entries for users whose names start with viptela-reserved- Names starting with viptela-reserved- belong to reserved system service accounts. Any one character in the request can be encoded, so %6a is only an example. The same entries can also appear during normal operation, and each match has to be checked against normal activity to avoid false positives. To help determine whether a Manager has been compromised, customers can open a Severity 3 case with Cisco TAC and include CVE-2026-76504 in the title. Cisco asks them to run request admin-tech on the Manager first, so the output file can be reviewed. The advisory includes no detection rule and does not say whether upgrading removes an attacker who already has access. Cisco's advisories for the May flaw and the first June flaw said an update alone would not resolve a confirmed compromise. They told customers to collect the admin-tech file before upgrading. CVE-2026-76504 follows a series of Cisco SD-WAN flaws flagged as exploited this year. As of September 30, the U.S. Cybersecurity and Infrastructure Security Agency's (CISA) Known Exploited Vulnerabilities catalog listed eight Cisco SD-WAN flaws added in 2026.

PHP has released emergency updates that fix two critical flaws in the language itself, letting an attacker without an account run code on a web server. The fixes are in PHP 8.5.12, 8.4.27, 8.3.36 and 8.2.35, and the PHP team says only updating fully protects a server. The flaws, together called PHP2Shell, sit in the PHP runtime, not in any application, so a site is exposed even when its own code is secure. The risk is highest on servers using Apache's mod_php, where a working exploit triggers the attack before any application code runs. Both flaws are rated 9.2 on the CVSS v4.0 scale and carry the identifiers CVE-2026-109618 and CVE-2026-109619. PHP published them around the scheduled release time of 14:00 UTC on October 21, a day after details leaked ahead of a planned October 22 disclosure. Researchers at Wiz, Calif, and OpenAI found and reported the flaws, which affect nearly every PHP version back to PHP 5.4. Who Is Affected Every PHP installation that serves web requests is at risk, including PHP-FPM, Apache mod_php, php-cgi, FrankenPHP and LiteSpeed, according to the PHP security advisory. Because the flaws are in the engine rather than in any site's code, even a simple "Hello World" page on a vulnerable PHP version can be attacked. The advisory singles out mod_php as the highest risk, with a demonstrated exploit in which a single unauthenticated request triggers the attack before any application code runs. PHP-FPM behaves differently, because it shuts the worker down when a request fails early in setup. For one of the two flaws, PHP's own analysis supports that FPM is susceptible but says no complete FPM exploit has been shown; the second flaw was shown to reach code execution on both mod_php and PHP-FPM, though the FPM path there depends on an operation inside the running application. An attacker can also read memory from the PHP worker process, which may hold passwords, authentication tokens, API keys, and certificates belonging to other requests, without first gaining code execution. The researchers demonstrated this reading of live worker memory against applications they did not control, making it independent of the application running on top of PHP. What to Install Update the PHP runtime that serves web requests, then restart Apache, PHP-FPM, and any long-running PHP workers. Updating an application such as WordPress or Laravel does not update the PHP runtime beneath it; that comes from the server package, the host, or the container image. PHP 8.1 and older no longer receive updates from the PHP project, and PHP 8.2 reaches end of life on December 31, 2026. For the older branches, the PHP security team has published source backports for PHP 7.4, 8.0, and 8.1 to help people building from source or waiting on a vendor. Linux distributions and long-term-support vendors received the patches in advance, so a distribution package can carry the fix under an old-looking version number; check the package changelog for the CVE, as Debian advises, not the version string. If You Cannot Update Yet Only updating is a complete fix. The measures below reduce exposure to specific attack paths and do not make a server safe, according to the advisory. For CVE-2026-109618, set memory_limit=-1 so applications cannot override it, keep post_max_size low, and enforce request-size limits at the web server or proxy. Do not use RLIMIT_AS or RLIMIT_DATA as a substitute, because PHP warns they can trigger the same vulnerable path. For CVE-2026-109619, set session.upload_progress.enabled=0 and restart every worker, and on PHP 8.5 also set fatal_error_backtraces=0. Turning off session upload progress blocks the confirmed session paths but not other variants, and no configuration change fully mitigates this flaw short of updating. That setting is the one circulated as a workaround before the patch, and the release confirms it was never a complete fix. Session upload progress is turned on by default and can reach session handling before PHP finishes setting up a request, which is why it takes part in one confirmed attack path for CVE-2026-109619 and why turning it off does nothing for CVE-2026-109618. "The only thing I can say is that the only mitigation is patching/upgrading PHP. I sadly know too much," PHP core developer Gina Peter Banyard wrote before the release, replying to someone who suggested the setting might be enough. After updating, review your memory settings. The fix adds a new hard memory limit, and reaching it ends the process and stops shutdown handlers from running, so check memory_limit and post_max_size against what your application needs. If you already patched but suspect an earlier break-in, the researchers suggest watching for unusual multipart requests followed by memory-limit errors or repeated HTTP 500 responses, oddly large PHPSESSID response cookies, and unexplained restarts of PHP workers. Is It Being Attacked Before the patch shipped, Cloudflare said it was seeing early attempts to exploit the flaws. "We are seeing early attacks emerging and are updating mitigations as new vectors show up," Cloudflare CTO Dane Knecht said, calling the firewall rules Cloudflare deployed a stopgap and urging administrators to patch. No source has confirmed a successful break-in. watchTowr, which reproduced CVE-2026-109618, reported no exploitation in the wild as of 11:26 UTC on October 21, and neither flaw was in CISA's Known Exploited Vulnerabilities catalog at that time. Some organizations took services offline as a precaution rather than in response to any break-in. BambooHR took its service offline across the United States, Canada and Ireland, warned that payroll would be interrupted, and said it did not yet have a restoration time. In the Netherlands, MijnOverheid, DigiD, the lower house of parliament's site, the national cyber-security center and several education systems went offline, the broadcaster NOS reported; the centre said it had not seen the flaw abused but urged everyone to patch. How It Came Out A leak pulled the release forward. On October 20, as The Hacker News reported, a post on Hacker News said two PHP remote code execution flaws, with the two CVE identifiers, were set for disclosure on October 22, on no more than a trusted tip. PHP posted an advance notice that evening and moved the release to October 21. The leak's claim of a CVSS 10.0 score was not PHP's; PHP rates both flaws 9.2. The flaws were found by Wiz Research, Calif, and OpenAI's Codex Security team, working with the PHP security team and Google's Gemini team on the fix. The underlying code had been in PHP for more than a decade. The researchers say AI models helped turn these long-standing flaws into working exploits, letting one researcher do in about a week what they say would otherwise have taken a team months. Calif, which traced the bug's lineage to PHP research from 2004, says knowing the target's history still mattered, and that current models do not reliably start from obscure, twenty-year-old primitives on their own. Update: watchTowr Reports Exploitation Attempts, Still No Confirmed Break-In watchTowr, which earlier in the day reported seeing none, said in a new advisory at 14:19 UTC on October 21 that it is observing "active exploitation attempts" of both CVE-2026-109618 and CVE-2026-109619. Cloudflare said it saw attack traffic against its customers and watched attackers change their payloads to get around its firewall rules, which it had switched on by default at 03:02 UTC, before the patch. No source has reported a confirmed break-in of a specific server as of this update. The PHP Foundation said the coordinated disclosure came apart before the release. Around 20:00 UTC on October 20, the research firm Calif mistakenly posted a video of its working proof of concept, and at 07:41 UTC on October 21, about six hours before the fix shipped, the vendor Chainguard published built images containing the patch, letting anyone study the fix while other users waited to update. Update: PHP Foundation Says a 2024 Audit Found the First Signs of the Flaw In the same post, the PHP Foundation said a core developer first found signs of the out-of-memory flaw behind CVE-2026-109618 during PHP's 2024 external audit, but a working attack was only theorized and no concrete route to code execution was found then. Competing fixes each risked breaking compatibility, opening denial-of-service paths, or forcing changes on third-party extensions, and a small team struggled to agree, so work on a fix stalled for months. The Foundation called the delay "a structural failure" of its decision process and its resources. The 2026 reports from Calif, OpenAI and Wiz, which used AI tools, established the working exploit that made the flaw's full impact clear and moved the fix to the top of the queue. The Foundation said it has since changed how it makes security decisions and added staff and tooling to catch similar problems sooner. (The story was updated after publication on October 21, 2026, to add later reports of exploitation attempts and the PHP Foundation's account of the flaw's history.)

History: 22/09/2026 --- v1.0 -- Initial publication Summary On 22 September 2026, F5 published an advisory addressing a critical vulnerability affecting its BIG-IP APM product. The vendor confirmed active exploitation in the wild [1]. CERT-EU recommends taking appropriate actions as soon as possible. Technical Details The vulnerability CVE-2026-94127, with a CVSS score of 9.8, is a heap-based buffer overflow vulnerability and allow unauthenticated attacker to achieve remote code execution (RCE) on the affected device [1]. Affected Products The vulnerability affects the following versions of BIG-IP APM if configured with an access policy and an OAuth profile on a virtual server [1]: 17.1.0 - 17.1.3 17.5.0 - 17.5.1 21.1.0 Recommendations CERT-EU recommends taking the following actions as soon as possible: Preserve forensic evidence. Apply the relevant hotfix. Check for signs of compromise (see the compromise assessment section). If any sign of compromise is detected, start the incident response process. Mitigation If patching cannot be applied immediately, F5 provides an iRule-based mitigation for the affected virtual server. To obtain it, F5 BIG-IP clients should contact the F5 support [1]. Compromise Assessment CERT-EU strongly advises to look for the following indicators of compromise provided by the vendor in its advisory [1]: At a high level, multiple OAuth authentication failures, followed by suspicious commands, shortly followed by a TMM SIGABRT is the combination that should lead to human review of the system. OAuth authentication failures: check /var/log/apm for repeated occurrences of the following, especially 10 or more from a single IP in a short window. err tmm1\[30975\]: 01990004:3: : Request UserInfo from Source ID (null) IP failed. Error Code (invalid\_token) Error Description (The access token is invalid.) - Increase of OAuth failure statistics. Run the following and look for an unexplained increase in total_failed : $ tmctl global_oauth_stat -s total_requests,total_userinfo_requests,total_failed - Audit log anomalies: if OAuth failures are observed, review /var/log/audit around those timestamps for suspicious commands. TMM core files: Presence of a TMM core file alone is not an indicator, but core files should be investigated. The vendor indicates that they have observed TMM entering a loop, which causes the SOD daemon to send a SIGABRT.

The public still doesn’t know who is abusing a critical Citrix vulnerability exploited as a zero-day weeks before disclosure, but we now know that the unknown digital intruders have used CVE-2026-88772 to break into government agencies, financial services firms, education organizations, and legal and professional services sectors across North America and Europe. And everyone agrees that the vendor took way too long to disclose the security holes. GreyNoise said it spotted an attempt to exploit CVE-2026-88771 against a Citrix NetScaler Gateway on September 24. Google researchers, meanwhile, said the CVE-2026-88772 campaign has been ongoing “since at least early September.” “Why Citrix took so long to disclose these vulnerabilities is a question only Citrix can answer,” Benjamin Harris, founder and CEO of exposure management firm watchTowr, told The Register. Citrix declined to answer The Register's questions about the scope of the attacks, and why it didn't alert the public about the CVEs under active exploitation until Sunday. “The vulnerabilities were discovered during incident response and forensic investigations at organizations already compromised, meaning both the exploitation and Citrix’s awareness of it predated public disclosure,” Harris said. “Citrix has a history of delaying the publication of vulnerabilities, even when they’re being exploited in the wild and affecting customers.” So if you use Citrix NetScaler ADC and NetScaler Gateway appliances, and haven’t already applied the security updates, do that ASAP. But first, check your systems for signs of compromise, warns Mandiant Consulting CTO Charles Carmakal. “Given the active exploitation, NetScaler customers should prioritize examining their systems for compromise *before* upgrading/patching,” Carmakal said on LinkedIn. “If you find evidence of web shells or other malicious files, please preserve evidence and investigate the scope of the compromise. Patching alone may not eradicate the threat actor from your environment.” No attribution - yet Citrix disclosed eight CVEs on Sunday with the worst of the bunch – CVE-2026-88771 and CVE-2026-88772 – earning critical 9.5 CVSS scores. “Exploitation of CVE-2026-88771 and CVE-2026-88772 on unmitigated NetScaler deployments has been observed,” the vendor said. CVE-2026-88771 can allow an unauthenticated attacker to execute arbitrary commands remotely. CVE-2026-88772 is a memory overflow vulnerability that can lead to remote code execution or denial of service when DTLS is enabled, as it is by default on VPN virtual servers. But by the time Citrix issued security advisories and warned customers about the vulnerabilities, they were already under attack. “No attribution has been made public, and we have yet to identify a clear trend among targets by industry or organization size,” Harris said. “Historically, NetScaler vulnerabilities have been exploited by both state-sponsored groups and ransomware operators.” WatchTowr on Tuesday published a technical writeup about CVE-2026-88772, plus a detection artifact generator for Citrix users to determine if they are vulnerable and to help with remediation. Also on Tuesday, Google’s threat intel businesses provided additional details about the exploitation campaign’s targets and the attacker’s custom malware. “We have observed evidence that organizations in North America and Europe in the government, financial services, education, legal and professional services sectors were likely impacted by this exploitation campaign, which has been ongoing since at least early September,” Google Threat Intelligence Group and Mandiant said in an advisory. Custom malware After analyzing the intruder’s post-exploit toolkit, the malware hunters found never-before-seen malware used to establish persistent root access and proxy traffic into internal corporate networks. The custom malware includes WHIPSHOT, a PHP web shell, and SLAPSHOT, a TCP tunneling tool written in Python. WHIPSHOT is disguised as a Debian package and hides Base64-encoded command-and-control payloads in native HTTP headers. It functions as an HTTP transport bridge for SLAPSHOT, which accepts commands from WHIPSHOT and forwards arbitrary TCP streams to internal hosts. Supported commands include: open, which establishes an outbound TCP socket to a target host and port. push, which writes data to an open session. pull, which polls and reads data from an open session socket. exch, which sends and receives command-and-control data to and from an open session socket. close, which terminates a specified network session. ping, which performs a basic health-check verification. “In at least one observed intrusion, the threat actor routed traffic through this proxy to manually conduct internal reconnaissance and credential theft,” the threat intel teams noted. Google did not immediately respond to The Register’s questions about the campaign, including how many exploitation attempts and successful intrusions its threat hunters observed. Its advisory notes that the Citrix campaign “underscores the continued targeting of edge devices to gain initial access to victim networks, a trend that GTIG has tracked across a range of threat actors.” Security and networking vulnerabilities accounted for about half of enterprise-related zero-days in 2025, according to Google’s count. Attackers love edge devices - application delivery controllers, VPN gateways, and firewalls - because they provide direct access from the open internet to corporate networks, allowing attackers to bypass endpoint detection tools and other security layers. NetScaler, in particular, is notoriously buggy. Attackers exploited another critical NetScaler vuln in March. A year earlier, Citrix disclosed multiple zero-days in the same product. ®