CVE-2026-64211: Linux kernel · srcu: Don't queue workqueue handlers to never-online CPUs
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 5.5 Medium · fixed in 7.0.0-28.28~24.04.1 : update Linux kernel when convenient.
Data as of 26 Oct 2026, 12:55 UTC
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 3% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 7.0.0-28.28~24.04.1, 7.0.0-28.28, 7.0.0-1009.9 +5
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 27 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Patches and advisories
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-gkepkg:deb/ubuntu/linux-gke?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A patch is available and should be applied to affected Linux kernel versions to prevent queueing workqueue handlers on CPUs that have never been online. The vendor advisory from Ubuntu confirms that this issue has been fixed. Systems running affected versions should update to the fixed kernel releases. No additional mitigation is required beyond applying the official fix.
Description
A vulnerability in the Linux kernel's srcu subsystem could cause hangs on s390 architectures by queueing workqueue handlers to CPUs that have never been online, including imaginary CPUs. This issue arises during the transition of an srcu_struct from CPU-0 to all-CPUs state, where callbacks may be invoked on CPUs not fully online. The fix prevents queueing handlers on such CPUs and redirects callbacks to the boot CPU. This vulnerability has a medium severity with a CVSS score of 5.5 and affects multiple Linux kernel versions.
References
- ubuntu.com/security/CVE-2026-64211 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-64211 (opens in a new tab)
- git.kernel.org/linus/593889c401426004bd0ea0f6d4fcece728b03420 (opens in a new tab)
- git.kernel.org/stable/c/593889c401426004bd0ea0f6d4fcece728b03420 (opens in a new tab)
- git.kernel.org/stable/c/a4153538fcd2361c4e0039eb103265492d26044e (opens in a new tab)
- ubuntu.com/security/notices/USN-8618-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8663-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8664-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8728-1 (opens in a new tab)