VulnerabilityPublished 23 Oct 2026

CVE-2026-99065: Linux kernel · cgroup/cpuset: Handle cpu hotplug race in guarantee_active_cpus()

Source GCVE Database

Authoritative record:CVE-2026-99065· Medium

Not known to be exploited · fixed in a21c255159bfe0034740292e10d2e258feeeb10d : update Linux kernel when convenient.

Data as of 26 Oct 2026, 13:47 UTC

Severity

Medium

Rated by Threat Radar · 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.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-px5v-f8qg-w5f8

What to do

Upgrade Linux kernel to a21c255159bfe0034740292e10d2e258feeeb10d, 23b1ab15ca91f2cffaf149d9bb0fafeb700c7db2 or 8d88d3221204fbb1b6dc2c0f2f2181fe49126639.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 7a0aabd9ce697fc581ec691b21f748050fbcf004, < a21c255159bfe0034740292e10d2e258feeeb10d	Fixed in a21c255159bfe0034740292e10d2e258feeeb10d
LinuxLinux	Affected ≥ 7a0aabd9ce697fc581ec691b21f748050fbcf004, < 23b1ab15ca91f2cffaf149d9bb0fafeb700c7db2	Fixed in 23b1ab15ca91f2cffaf149d9bb0fafeb700c7db2
LinuxLinux	Affected ≥ 7a0aabd9ce697fc581ec691b21f748050fbcf004, < 8d88d3221204fbb1b6dc2c0f2f2181fe49126639	Fixed in 8d88d3221204fbb1b6dc2c0f2f2181fe49126639
LinuxLinux	Affected =6.16	Fixed in–

Description

In the Linux kernel, the following vulnerability has been resolved: cgroup/cpuset: Handle cpu hotplug race in guarantee_active_cpus() With commit 2125c0034c5d ("cgroup/cpuset: Make cpuset hotplug processing synchronous"), the cpuset hotplug operation becomes synchronous. That commit also removes the code that handles race between cpuset_hotplug_work and cpu hotplug notifier with the assumption that race is now gone. Later commit 7a0aabd9ce69 ("cgroup/cpuset: Always use cpu_active_mask") updates the cpuset code to always use cpu_active_mask instead of cpu_online_mask in some places including guarantee_online_cpus() which is renamed to guarantee_active_cpus() in that commit. In the case of CPU offline operation, cpu_active_mask is updated first in sched_cpu_deactivate() to remove the offline CPU before cpuset_handle_hotplug() is called to update the effective_cpus of the affected cpusets. The cpu_online_mask is updated after that near the end of the offline operation to remove the offline CPU. As a result, the race comes back and the top cpuset may not have any active CPU leading to NULL pointer dereference during the race window when guarantee_active_cpus() is called after cpu_active_mask is updated to remove the CPU to be torn down but before cpuset_handle_hotplug() is able to properly update the effective_cpus of the top cpuset. Fix this by adding back the NULL cs check to avoid this problem.

References

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