CVE-2026-89695: Linux kernel · nfsd: cap decoded POSIX ACL count to bound sort cost
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 7.5 High.
Data as of 26 Oct 2026, 14:05 UTC
- EPSS
- 0.4% chance of exploitation in 30 days – higher than 41% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HExploitation 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 adds validation to reject POSIX ACL counts exceeding NFS_ACL_MAX_ENTRIES before allocation and sorting, preventing unbounded CPU usage. Users should apply the updated Linux kernel versions that include this patch. No additional mitigation is required as the vulnerability is addressed by this official fix.
Description
A vulnerability in the Linux kernel's NFS server (nfsd) component allows a client to specify an unbounded POSIX ACL entry count, leading to an unbounded CPU usage due to an O(n^2) bubble sort operation. This occurs because the decoder function nfsd4_decode_posixacl() reads a u32 count from the wire without capping it, unlike the encoder side. The issue has been fixed by adding a check to reject counts exceeding NFS_ACL_MAX_ENTRIES before allocation and sorting, preventing excessive CPU consumption.
References
- nvd.nist.gov/vuln/detail/CVE-2026-89695 (opens in a new tab)
- git.kernel.org/stable/c/4bc1108e876153a2dd6d874052b99182c3603135 (opens in a new tab)
- git.kernel.org/stable/c/ea14d71d6ecb925673761bcf79f781f7dc9042cc (opens in a new tab)
- ubuntu.com/security/CVE-2026-89695 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-89695 (opens in a new tab)
- git.kernel.org/linus/4bc1108e876153a2dd6d874052b99182c3603135 (opens in a new tab)