CyberSecBulletin
CVE-2026-31709NVD status: Modified

Linux: Out-of-bounds Read

Published Updated By the CyberSecBulletin desk

CVE-2026-31709 is a high-severity out-of-bounds read vulnerability in Linux, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists versions b8603d9ae6c9087662b098619996bc4a8064319d, c2abdebf72000a64603ced84d36ccbd164f11391, 8e47d297e7cf9a6029a0d38e7b22faba7d7aaf12 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.34% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to b8603d9ae6c9087662b098619996bc4a8064319d or c2abdebf72000a64603ced84d36ccbd164f11391 or 8e47d297e7cf9a6029a0d38e7b22faba7d7aaf12 or d92f3f0b22414e7515696a02224d0af55e3004a3, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 7.0.2 or a later version.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
  4. Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxbc3e9dd9d104ca1b75644eab87b38ce8a924aef4 up to, but not including, b8603d9ae6c9087662b098619996bc4a8064319d; bc3e9dd9d104ca1b75644eab87b38ce8a924aef4 up to, but not including, c2abdebf72000a64603ced84d36ccbd164f11391; bc3e9dd9d104ca1b75644eab87b38ce8a924aef4 up to, but not including, 8e47d297e7cf9a6029a0d38e7b22faba7d7aaf12; bc3e9dd9d104ca1b75644eab87b38ce8a924aef4 up to, but not including, d92f3f0b22414e7515696a02224d0af55e3004a3; bc3e9dd9d104ca1b75644eab87b38ce8a924aef4 up to, but not including, ff0ca46b13b9ef6edbcd238a3b6caacfef8ba0e5; bc3e9dd9d104ca1b75644eab87b38ce8a924aef4 up to, but not including, b78db9bddc84136f6a0bb49e8883cf200dfb87a8; bc3e9dd9d104ca1b75644eab87b38ce8a924aef4 up to, but not including, 0a8cf165566ba55a39fd0f4de172119dd646d39a; 5.12b8603d9ae6c9087662b098619996bc4a8064319d, c2abdebf72000a64603ced84d36ccbd164f11391, 8e47d297e7cf9a6029a0d38e7b22faba7d7aaf12, d92f3f0b22414e7515696a02224d0af55e3004a3, ff0ca46b13b9ef6edbcd238a3b6caacfef8ba0e5, b78db9bddc84136f6a0bb49e8883cf200dfb87a8
Red HatRed Hat Enterprise Linux 10Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 10.0 Extended Update SupportNot specified in the recordNot stated
Red HatRed Hat Enterprise Linux 8Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 9Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 9.2 Update Services for SAP SolutionsNot specified in the recordNot stated
Red HatRed Hat Enterprise Linux 9.4 Update Services for SAP SolutionsNot specified in the recordNot stated
Red HatRed Hat Enterprise Linux 9.6 Extended Update SupportNot specified in the recordNot stated
Red HatRed Hat Enterprise Linux 6Not specified in the recordNot stated
Red HatRed Hat Enterprise Linux 7Not specified in the recordNot stated
SiemensSIMATIC S7-1500 TM MFP - GNU/Linux subsystemall versionsNot stated
LinuxLinux Kernel5.12 up to, but not including, 7.0.27.0.2

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
RequiredA user must take an action such as opening a file or link.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. Scored by CNA.

Scoring systemScoreSeverityScored by
CVSS 3.18.8HighCNA
CVSS 3.17.8HighCNA

Official description

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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Out-of-bounds Read

The product reads data past the end, or before the beginning, of the intended buffer.

How developers prevent this class of flaw

  • Use a language that provides appropriate memory abstractions.

More Out-of-bounds Read vulnerabilities (CWE-125)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Recent Out-of-bounds Read vulnerabilities

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