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VulnerabilityPublished Updated

CVE-2026-31712: Linux kernel · ksmbd: require minimum ACE size in smb_check_perm_dacl()

Affects Linux kernelSource GCVE Database

0

Not known to be exploited · CVSS 8.3 High · fixed in 5.15.0-1117.124~20.04.1 : patch Linux kernel soon.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score
8.3High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 25% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 5.15.0-1117.124~20.04.1, 5.15.0-1123.132~20.04.1, 5.15.0-1122.131~20.04.1 +69
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 1 May 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

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
Ubuntu 26.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-27.27
Fixed in
  • 7.0.0-27.27
Ubuntu 26.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-1008.8
Fixed in
  • 7.0.0-1008.8
Ubuntu 26.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-1010.10
Fixed in
  • 7.0.0-1010.10
Ubuntu 26.04 LTSlinux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-1009.9
Fixed in
  • 7.0.0-1009.9
Ubuntu 26.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-1007.7
Fixed in
  • 7.0.0-1007.7
Ubuntu 26.04 LTSlinux-ibmpkg:deb/ubuntu/linux-ibm?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-1009.9
Fixed in
  • 7.0.0-1009.9

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A patch is available and should be applied to affected Linux kernel versions to correct the validation of ACE sizes in smb_check_perm_dacl(). The fix enforces a minimum ACE size and rejects malformed ACEs that could cause out-of-bounds reads. Systems running affected versions should upgrade to the fixed kernel releases as per vendor advisories such as Ubuntu Security Notice USN-8488-1. No additional mitigations are required beyond applying the official fix.

Description

A vulnerability in the Linux kernel's ksmbd component allows an authenticated SMB client with permission to set an ACL on a file to trigger an out-of-bounds (OOB) read during permission checks. This occurs because the smb_check_perm_dacl() function does not properly validate the minimum size of Access Control Entries (ACEs) in a discretionary ACL (DACL), allowing crafted ACEs with undersized declared sizes to bypass checks and cause OOB reads. The issue can lead to kernel state corruption and is triggered on subsequent file CREATE operations. The vulnerability is not exploitable pre-authentication and does not leak data directly to the attacker. A fix is available in updated Linux kernel versions.

References

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