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🛡️ CVE-2026-31709 — kernel

🟠 CVSS 8.8 — High ✅ No Known Exploit NVD
8.8
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

smb: client: validate the whole DACL before rewriting it in cifsacl

In the Linux kernel, the following vulnerability has been resolved:

smb: client: validate the whole DACL before rewriting it in cifsacl

build_sec_desc() and id_mode_to_cifs_acl() derive a DACL pointer from a

server-supplied dacloffset and then use the incoming ACL to rebuild the

chmod/chown security descriptor.

The original fix only checked that the struct smb_acl header fits before

reading dacl_ptr->size or dacl_ptr->num_aces. That avoids the immediate

header-field OOB read, but the rewrite helpers still walk ACEs based on

pdacl->num_aces with no structural validation of the incoming DACL body.

A malicious server can return a truncated DACL that still contains a

header, claims one or more ACEs, and then drive

replace_sids_and_copy_aces() or set_chmod_dacl() past the validated

extent while they compare or copy attacker-controlled ACEs.

Factor the DACL structural checks into validate_dacl(), extend them to

validate each ACE against the DACL bounds, and use the shared validator

before the chmod/chown rebuild paths. parse_dacl() reuses the same

validator so the read-side parser and write-side rewrite paths agree on

what constitutes a well-formed incoming DACL.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. A user must be tricked into taking some action. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality high, integrity high, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: Required — someone has to click, open or visit something.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: High — total loss, or loss the attacker controls.
  • Integrity impact: High — total loss, or loss the attacker controls.
  • Availability impact: High — total loss, or loss the attacker controls.

Affected software

CVE-2026-31709 is recorded against 2 packages.

  • kernel (from 6.19.0 up to 7.0.2)
  • linux-kernel (from 5.12 up to 7.0.2)

Timeline and source

Published on 1 May 2026 and last revised on 12 August 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

git.kernel.org (Web)
git.kernel.org (Web)
git.kernel.org (Web)
git.kernel.org (Web)
git.kernel.org (Web)
git.kernel.org (Web)
git.kernel.org (Web)
security.access.redhat.com (Web)
access.redhat.com (Advisory)
access.redhat.com (Advisory)
access.redhat.com (Advisory)
access.redhat.com (Advisory)
access.redhat.com (Advisory)
access.redhat.com (Advisory)
access.redhat.com (Advisory)
access.redhat.com (Advisory)
access.redhat.com (Advisory)
access.redhat.com (Advisory)
github.com (Advisory)
nvd.nist.gov (Advisory)
bugzilla.redhat.com (Report)
git.kernel.org (Package)

Other advisories for this package

kernel has other advisories on record. If you are patching this one, these are worth checking on the same host:

Details

Severity High
CVSS Score 8.8
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CWE N/A
Public Exploit ✅ No
Source NVD
Published 2026-05-01
Updated 2026-08-20
Modified 2026-08-12

Affected Packages

Software From version Fixed in
kernel 6.19.0 7.0.2
linux-kernel 5.12 7.0.2

References

Similar Threats

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