CVE-2026-89661: Linux kernel · NFSD: Prevent post-shutdown use-after-free in unlock_filesystem
Affects Linux kernelSource GCVE Database
Not known to be exploited.
Data as of 26 Oct 2026, 14:05 UTC
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
Disclosed: evidence found.
CVE published 11 Sep 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
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 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
- nvd.nist.gov/vuln/detail/CVE-2026-89661 (opens in a new tab)
- git.kernel.org/stable/c/0c1a755b7212e0835398d4df5e782ea85ccd7476 (opens in a new tab)
- git.kernel.org/stable/c/292d915d3ba6fd15eeb88351fa10581683073109 (opens in a new tab)
- ubuntu.com/security/CVE-2026-89661 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-89661 (opens in a new tab)
- git.kernel.org/linus/292d915d3ba6fd15eeb88351fa10581683073109 (opens in a new tab)