Atlassian urges immediate patching of critical Data Center file access vulnerability (CVE-2026-21589)

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.

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. ®

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.

Reportedly , the ShinyHunters extortion group breached the leak site of one of its competitors, the Clop ransomware gang. ShinyHunters is a financially motivated cybercrime and extortion group active since 2019. It is known for stealing large volumes of data and pressuring victims to pay, rather than necessarily deploying ransomware. One recent high-profile organization targeted by the group was Instructure, the maker of Canvas LMS. ShinyHunters claimed it stole 3.65 TB of data belonging to about 9,000 academic institutions . Clop, also written Cl0p, is a ransomware and data-extortion operation associated with large-scale exploitation of vulnerabilities in enterprise software and file-transfer platforms. In its recent campaign targeting PTC Windchill systems, it named more than 40 alleged victims, including Shell, Philips, Fiserv, Zebra Technologies, Ingersoll Rand, and Toast. At the time of writing, the Clop dark web leak site looks like this: Domain seized by ShinyHunters The rest of that page looks much the same as the ShinyHunters leak site, which includes this “Note to Cl0p”: “Note to Cl0p_- 21 Sep UPDATE: Every 24 hours you fail to engage with us the demands increase. The demand now includes a mandatory apology issued directly to me PUBLICLY . I am 3-0 against you rich and broke criminals. UPDATE, 20 Sep, 1:39 a.m ET: Dear Likhogray & Tarasov, tell your boss j0nny to wake the fuck up. Run those pockets. I want all the money you made off the EBS campaign plus more AND WITH INTEREST, before I start releasing information regarding the companies that paid you, how much, and to what Bitcoin address. My phone book contains all major financial media outlets. CLOCK IS TICKING! LETS GET THE BALL ROLLING! Be sure to bring an English interlocutor so you can comprehend my literacy in acquiring your bank account. 66 hours remaining. [19 Sep]: IF YOU WANT TO SAVE YOUR BRAND AND NOT DIE BY MY HANDS: Email us from your official email at [email protected] and lets see how wealthy you really are. 2.333% of my networth is a 8 figure amount, I hope you can pay that much because that is the demand, negotiable. Get your bosses in front of the white board in the war room. Clock is ticking moron. Kindly excuse our unprofessionalism. Updated: 21 Sep 2026” BleepingComputer reports that the attack began Friday night when ShinyHunters exploited what it claims is an unauthenticated file-upload vulnerability in Grav CMS to upload a small text file to Clop’s site. Several hours later, ShinyHunters told BleepingComputer that it had “completely defaced” the site. The group claimed it could continue controlling the address: “We have their onion keys. So, if they kick us out it wouldn’t matter at all because we control the private keys to host the same exact onion URL.” You might expect groups that make their money by exploiting unpatched vulnerabilities to be more vigilant about their own systems, but it looks as though they sometimes let their guard down. According to ShinyHunters, this gang war began after ShinyHunters disrupted a Clop data-theft campaign. A Clop representative then allegedly threatened to identify ShinyHunters members and made violent threats against them. ShinyHunters explained: “During the Oracle EBS campaign they ran and stole from me last year, someone from cl0p personally messaged me and said, and I quote (translated from Russian): I have more money than you and all of your people combined, I’ll kill you soon.” The good news is that while they are after each other, they probably have less time to attack legitimate businesses. I’m grabbing a bag of popcorn and watching this one unfold. We’ll keep you posted. From reporting threats to removing them. Cybersecurity risks should never spread beyond a headline. Keep threats off your devices by  downloading Malwarebytes today .

Authorities in the Netherlands have arrested a 24-year-old convicted cybercriminal on suspicion of aiding in data thefts and extortions by the prolific hacker group ShinyHunters . In the days immediately following the suspect’s arrest, remaining ShinyHunters members dramatically escalated their attacks, stealing highly sensitive data from the FBI and extorting the Russian ransomware group Cl0p . According to three sources familiar with the matter, the Dutch man arrested by authorities this month is Pepijn van der Stap , a convicted cybercriminal from Almere and Lelystad in the Netherlands. Van der Stap was previously convicted in 2023 in connection with a string of data thefts and extortions that prosecutors said earned between €1.5 million and €2.7 million. At his trial in late 2023, van der Stap admitted that he lived a Dr. Jekyll and Mr. Hyde existence, secretly using the hacker handle “ Umbreon ” to extort victims and post their data on English language hacking communities like the now-defunct RaidForums and Breached. By day, however, van der Stap was working as a software engineer at the Amsterdam-based cybersecurity startup Hadrian , while volunteering at the Dutch Institute for Vulnerability Disclosure (DIVD), a nonprofit security research group. Pepijn van der Stap’s alter ego “Umbreon” selling a database on RaidForums, offering information on 2.3 million people from The Netherlands in September 2021. This user’s avatar is a depiction of the Pokemon character Umbreon. Image: KELA. Van der Stap confessed to his data theft and extortion activity, and was sentenced to four years in prison (one of which was suspended). During his trial, van der Stap opted to remain in custody for a time rather than at home, saying he could not find better treatment on the outside for his ongoing psychological issues, which he claimed included PTSD related to childhood trauma. He was released from prison in December 2025. In an interview with KrebsOnSecurity on September 9, 2026, Van der Stap cast himself as a reformed hacker who was trying to turn his life around and make a positive contribution to society. Van der Stap is currently employed as offensive security lead at the Dutch company Neo Security , which did not respond to requests for comment. Van der Stap said he was still dealing with civil lawsuits and restitution related to his previous cybercrime victims, and that he was trying his best to make amends. But not long after that interview, the Dutch hacker abruptly stopped replying to messages. Efforts by others close to him also repeatedly failed to elicit a response for the past two weeks. The LinkedIn profile for Pepijn van der Stap. According to two sources with knowledge of the matter, Van der Stap was arrested by Dutch authorities on or around September 16, and has been held in custody for questioning since. One source said a colleague of theirs personally witnessed Dutch authorities carting items out of Van der Stap’s residence. Authorities in the Netherlands have been asking the public for help in identifying the voice in a recorded telephone call from February 2026 in which a native Dutch-speaking ShinyHunters member social engineered their way into Odido , the nation’s largest mobile telecommunications provider. In that intrusion, ShinyHunters tricked an Odido employee into logging in at a spoofed website, and then used that access to steal data on more than 6.2 million Dutch people. Responding to Dutch news media, ShinyHunters confirmed that the suspect in the audio clip is indeed a member of the hacker collective. “Our team member has our full support – emotionally, mentally, and financially,” the hackers said. “Everything has been arranged, including a criminal defense lawyer. We do not look down on our staff and members; we take excellent care of them,” reads a statement ShinyHunters shared with NL Times . It remains unclear if the Dutch police have matched the Odido caller to a confirmed real-life identity. The Dutch police unit handling the Odido incident did not respond to requests for comment. The group also lashed out at the authorities in the Netherlands. “The Dutch police will need all the luck in the world – and everyone’s prayers – if they want to catch him before we carry out another large-scale data theft in the Netherlands,” the ShinyHunters statement said. “Frankly, the Dutch police are a big joke; they are incapable of doing anything. Incompetent. Irrelevant. Unimportant. Useless.” FBI, CL0P HACKS Just days after sources say Van der Stap was detained by Dutch authorities, ShinyHunters claimed credit for an unusually brazen breach at the FBI’s job application site apply.fbijobs.gov. According to reporting from 404 Media , the data stolen from the FBI site includes Social Security numbers and personal information on more than 5,000 officials. 404 Media and Reuters reported the FBI data included each person’s job title or team, such as special agent, threat intake examiner, major cybercrimes unit, and those investigating cyber threats from foreign state-backed actors. Reuters examined documents shared by ShinyHunters and found they included sensitive psychiatric and medical files of FBI staff. The FBI issued a brief statement confirming the hack. ShinyHunters said it gained access to the FBI site and other victims by exploiting a recently patched vulnerability (CVE-2026-35273) in PeopleSoft , a software-as-a-service platform from the software giant Oracle that is broadly used by companies to manage hiring and human resources, benefits and payroll. Oracle quickly issued a fix for the Peoplesoft vulnerability that ShinyHunters reportedly began exploiting as a zero-day in June, and at the time Mandiant released web application firewall rules intended for organizations who couldn’t apply the security update quickly enough. But on Friday, BleepingComputer reported that ShinyHunters used a URL-encoding trick to bypass Mandiant’s suggested web application firewall rules designed to mitigate the threat from the PeopleSoft flaw. In a report released Sept. 25, security experts at Mandiant and the Google Threat Intelligence Group (GTIG) confirmed that ShinyHunters had mass-exploited the PeopleSoft vulnerability to steal data from dozens of systems across a range of industries, including higher education, technology, healthcare, agriculture, transportation and government. Van der Stap’s former hacker alias Umbreon was hidden in plain sight throughout the imagery ShinyHunters used to spread news about the FBI hack: The defacement image that ShinyHunters left behind on the hacked FBI jobs site included an ASCII art design featuring the Pokemon character Umbreon. The message at the top read, “This site has been seized by ShinyHunters. rooting your systems since ’19 ;)” The image appears identical to a defacement message ShinyHunters used in their 2020 hack of the English-language cybercrime community Hackforums. The defacement message left by ShinyHunters on the FBI jobs site included an ASCII art rendition of the Pokemon character Umbreon. Image: Bleeping Computer. Multiple sources close to the ShinyHunters investigation said the group’s recent risky attacks against the FBI and one of Russia’s most venerated ransomware groups amounted to a major pivot away from the more measured tenor of the hacking gang’s operations. Those sources said the sudden shift came about after ShinyHunters was taken over by a teenage cybercriminal from Amman, Jordan who goes by the nickname Rey and operates as part of a cybercrime group called ScatteredLapsussHunters (SLSH), which experts say is an amalgamation of three hacking groups — Scattered Spider , LAPSUS$ and ShinyHunters . Those sources said Rey had an ongoing beef with the Dutch hacker over control of the ShinyHunters brand and data, and that the inclusion of the oversized Umbreon Pokemon image in the FBI jobs site defacement was likely an attempt by Rey to pin the hack on the Dutchman. Rey was first publicly identified by the cybersecurity firm KELA in March 2025. In advance of our November 2025 profile of Rey , KrebsOnSecurity messaged Rey’s father and asked for permission to interview his teenage son. Rey’s dad merely forwarded the message to his son, who admitted to participating in ransomware attacks and said he was trying to extricate himself from the SLSH hacker group. BLAMING UMBREON Immediately after news of the FBI jobs site hack was picked up in the media, Rey’s main account on Twitter/X (Ryan Moran/@rmoskovy) was taunting the Cl0p ransomware group and the FBI, crudely depicting them as the twin towers in New York being struck by planes labeled “cl0p drama” and “fbi breach claim.” In the foreground of the city is the giant Pokemon figure of Umbreon. A taunting meme uploaded to Twitter/X by Rey’s now-defunct account on Sept. 22. A giant float-sized version of the Pokemon character Umbreon can be seen in the bottom left. On Sept. 24, KrebsOnSecurity again contacted Rey’s dad, asking to interview him and his son for a story on Rey’s apparent ascendency as the head of ShinyHunters. Just hours after that request, Rey deleted his longtime Twitter/X account. Meanwhile, Rey’s dad, who works for the Royal Jordanian Airlines, has failed to respond to a half-dozen emailed requests for comment about his son’s alleged activities. Where does the bad blood between SLSH and ShinyHunters come from? According to a story in Wired this month, ShinyHunters and SLSH members briefly partnered earlier this year to help better monetize important stolen credentials collected by TeamPCP , an upstart group that was having great success compromising global code supply chains with malicious software but hadn’t been able to profit much from their stolen data (two alleged leaders of TeamPCP were arrested last month in Australia , and in an interview the TeamPCP leader claimed they made just $20,000). The Wired story noted how Mandiant had infiltrated TeamPCP and was secretly responsible for having the crime group’s stolen credentials burned so quickly: Mandiant was secretly feeding those credentials to the major cloud providers like Amazon and Microsoft, who quickly invalidated the stolen keys. Meanwhile, the formerly cooperating hacker groups began to blame one another for causing the credentials to become worthless. Wired’s Andy Greenberg reported that a few weeks after partnering with TeamPCP, “ShinyHunters went rogue, carrying out its own extortions with TeamPCP’s credentials but without giving the supply-chain hackers their cut.” Mandiant researcher Austin Larsen told KrebsOnSecurity earlier this month that ShinyHunters has been enjoying a successful extortion spree so far this year, and is on track to pull in nearly $100 million in extortion payments from cybercrime victims in 2026. Van der Stap claims he was never motivated by money and that his earlier hacker activity was driven by a desire to have the world’s most complete collection of stolen databases. Speaking with reporters from Bloomberg in 2024, Van der Stap said that singular focus in turn fueled his desire to carry out cyberattacks. “The hacking was very easy for me, and it wasn’t a compulsion,” he told Bloomberg . “My habit was collecting. Collecting data, organizing data, downloading data, creating folders.” DIVD, the nonprofit security research group where Van der Stap previously served as a volunteer, disclosed on LinkedIn last week that the organization was dealing with an internal cybersecurity incident that appears to have involved the malicious use of artificial intelligence. DIVD has released few details about that incident, but a spokesperson for the nonprofit told KrebsOnSecurity it does not appear related to ShinyHunters, nor are there any signs the matter involves the work of a previous volunteer. Update: 3:44 p.m. ET: Corrected Van der Stap’s age, which is 24 (not 23). Update, 4:54 p.m. ET: The Dutch police have confirmed the arrest of a 24-year-old in connection with the ShinyHunters investigation. In a statement on Twitter/X , the Dutch police said the man will appear on Tuesday, September 29 before the chambers of the Rotterdam District Court, and that will provide more information tomorrow.

The Spectre microarchitecture vulnerability has returned yet again, this time to vex just-in-time (JIT) engines that generate machine code for browsers, runtimes, and kernels. The vulnerability is found in many CPUs that use speculative execution, the process of executing code before it is called to boost performance. Researchers found speculative execution opens the door to side channel attacks through which secrets can be exposed or inferred. When news of that risk became known, chipmakers and OS developers scrambled to fix these vulnerabilities, which were referred to as Spectre and Meltdown. And since then, researchers have found two or three dozen variations, such as 2025's VMScape, one of several so-called "Spectre v2" attacks that attempt to exploit indirect branch prediction, where program control is passed indirectly by pointing to an address where the next instruction can be found rather than specifying the instruction itself. The attacker trains the branch predictor to execute speculatively to a chosen address in order to leak data about the microarchitecture state. Researchers from Vrije Universiteit in the Netherlands and Scuola Superiore Sant’Anna in Italy have revived Spectre in a form called Branch Target Reuse (BTR), which they describe as the first practical in-place Spectre v2 attack that attacks just-in-time (JIT) compilers. An in-place attack is confined to the victim's branch while an out-of-place attack relies on speculation directed toward a target on a different branch. The researchers – Sander Wiebing, Yuhui Zhu, Alessandro Biondi, and Cristiano Giuffrida – found that this novel Spectre form can be conjured from code left in JIT engines including Linux cBPF, Oracle GraalVM, and Mozilla SpiderMonkey. "The key insight behind the attack is that, while modern CPUs restore architectural code coherence after self-modification, they do not necessarily invalidate stale indirect branch prediction entries (i.e., branch targets)," the authors explain. "In JIT engines, these stale targets can outlive the original code and later be reused when the code cache is repopulated, yielding a speculative execute-after-free primitive." The result is that an attacker can commandeer speculative control flow in a way that avoids some software defenses like FineIBT [PDF]. The authors showed they could exploit this flaw by designing two proof-of-concept exploits against an Intel-based Linux kernel that reveal the root password hash even with the constant binding defense provided by cBPF. The expected leakage rate is 5.7 KB/sec for Intel Raptor Cove chips and 5.4 KB/sec for Lion Cove. It's slow but enough for an unprivileged user to coax a sensitive password hash out of a vulnerable system. After the researchers disclosed their findings, Linux kernel developers and Oracle put mitigations in place. Two CVEs were assigned: CVE-2026-64507 and CVE-2026-64508. Mozilla, the researchers said, has opted to prioritize work on site isolation instead of addressing the issue directly. Strong mitigations like IBPB are said to be effective but add complexity and hinder performance. The Branch Target Reuse paper has been accepted for publication at the ACM Conference on Computer and Communications Security (CCS) 2026, which will be held November 15 through 19 in The Hague, Netherlands. ®