CVE-2026-99065: Linux kernel · cgroup/cpuset: Handle cpu hotplug race in guarantee_active_cpus()
Affects Linux kernelSource CVE Database V5
Not known to be exploited · fixed in a21c255159bfe0034740292e10d2e258feeeb10d : update Linux kernel when convenient.
Data as of 26 Oct 2026, 14:18 UTC
Rated Medium by Threat Radar's AI analysis · CVSS not yet scored by NVD
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 5% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in a21c255159bfe0034740292e10d2e258feeeb10d, 23b1ab15ca91f2cffaf149d9bb0fafeb700c7db2, 8d88d3221204fbb1b6dc2c0f2f2181fe49126639
Exploitation evidence
Disclosed: evidence found.
CVE published 23 Oct 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 Linux kernel to a21c255159bfe0034740292e10d2e258feeeb10d, 23b1ab15ca91f2cffaf149d9bb0fafeb700c7db2 or 8d88d3221204fbb1b6dc2c0f2f2181fe49126639.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in– |
AI-suggested
A fix is available and has been applied in the Linux kernel. The issue is resolved by adding a NULL pointer check in guarantee_active_cpus(). Users should update to the fixed kernel versions identified by the commits a21c255159bfe0034740292e10d2e258feeeb10d, 23b1ab15ca91f2cffaf149d9bb0fafeb700c7db2, and 8d88d3221204fbb1b6dc2c0f2f2181fe49126639. No additional mitigation is indicated.
Description
A race condition vulnerability in the Linux kernel cpuset subsystem was identified and fixed. The issue occurs during CPU offline operations where a race between updating cpu_active_mask and cpuset hotplug handling can lead to a NULL pointer dereference in guarantee_active_cpus(). This happens because the top cpuset may temporarily have no active CPU during the race window. The fix reintroduces a NULL check to prevent this condition.