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VulnerabilityPublished Updated

CVE-2026-89661: Linux kernel · NFSD: Prevent post-shutdown use-after-free in unlock_filesystem

Affects Linux kernelSource GCVE Database

0

Not known to be exploited.

Data as of 26 Oct 2026, 14:05 UTC

Severity
Medium

Rated by Threat Radar · CVSS not yet scored by NVD

EPSS
0.1% chance of exploitation in 30 days – higher than 9% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 11 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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

Affected software

ProductAffectedFixed in
Ubuntu 26.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=resoluteOther threatsAffected
  • 6.17.0-5.5 – 7.0.0-38.38
23 affected builds
Fixed in–
Ubuntu 26.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=resoluteOther threatsAffected
  • 6.17.0-1002.2 – 7.0.0-1014.14
15 affected builds
Fixed in–
Ubuntu 26.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=resoluteOther threatsAffected
  • 6.17.0-1003.3 – 7.0.0-1017.17
15 affected builds
Fixed in–
Ubuntu 26.04 LTSlinux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resoluteOther threatsAffected
  • 7.0.0-1003.3 – 7.0.0-1016.16
9 affected builds
Fixed in–
Ubuntu 26.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=resoluteOther threatsAffected
  • 6.17.0-1002.2 – 7.0.0-1014.14
13 affected builds
Fixed in–
Ubuntu 26.04 LTSlinux-gkepkg:deb/ubuntu/linux-gke?arch=source&distro=resoluteOther threatsAffected
  • 7.0.0-1002.3 – 7.0.0-1008.9
6 affected builds
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 fix is available that moves the asynchronous copy cancel operation into a protected section guarded by nfsd_mutex and confirms the server is running before proceeding. Users should apply the official kernel updates that include this fix. Since this is a local privilege issue, restricting local administrative access also mitigates risk.

Description

A use-after-free vulnerability in the Linux kernel's NFS daemon (NFSD) was resolved. The flaw occurs when writing a filesystem path to /proc/fs/nfsd/unlock_filesystem after the NFS server has shut down, leading to dereferencing freed memory. This can be triggered by a local administrator with CAP_SYS_ADMIN privileges. The fix involves moving the asynchronous copy cancel operation into a protected section that only runs when the server is active, preventing access to freed memory.

References

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