CyberSecBulletin
CVE-2026-31712NVD status: Modified

Linux: Out-of-bounds Write

Published Updated By the CyberSecBulletin desk

CVE-2026-31712 is a high-severity out-of-bounds write vulnerability in Linux, with a CVSS 3.1 base score of 8.3 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. The record lists versions 282cbbb476b9f35793452bc461934af4c7eca169, f20adc4ef7428bc485ee83fd1a592252fb87718b, 325d4ac11f526cb8964cff14548ccf02d8c756d8 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 0.32% 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 282cbbb476b9f35793452bc461934af4c7eca169 or f20adc4ef7428bc485ee83fd1a592252fb87718b or 325d4ac11f526cb8964cff14548ccf02d8c756d8 or 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 6.12.84 or 6.18.25 or 7.0.2, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinuxe2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, 282cbbb476b9f35793452bc461934af4c7eca169; e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, f20adc4ef7428bc485ee83fd1a592252fb87718b; e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, 325d4ac11f526cb8964cff14548ccf02d8c756d8; e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c; e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, 90089584b2e25c4510b7b987387b4405f0673ece; e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, 151b1799861fde38087c08f613abc2843ef597b0; e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9 up to, but not including, d07b26f39246a82399661936dd0c853983cfade7; 5.15282cbbb476b9f35793452bc461934af4c7eca169, f20adc4ef7428bc485ee83fd1a592252fb87718b, 325d4ac11f526cb8964cff14548ccf02d8c756d8, 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c, 90089584b2e25c4510b7b987387b4405f0673ece, 151b1799861fde38087c08f613abc2843ef597b0
SiemensSIMATIC S7-1500 TM MFP - GNU/Linux subsystemall versionsNot stated
LinuxLinux Kernel5.15 up to, but not including, 6.12.84; 6.13 up to, but not including, 6.18.25; 6.19 up to, but not including, 7.0.26.12.84, 6.18.25, 7.0.2

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
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
LowLimited modification of data is possible.
Availability
HighThe component can be taken down completely.

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

Official description

In the Linux kernel, the following vulnerability has been resolved: ksmbd: require minimum ACE size in smb_check_perm_dacl() Both ACE-walk loops in smb_check_perm_dacl() only guard against an under-sized remaining buffer, not against an ACE whose declared `ace->size` is smaller than the struct it claims to describe: if (offsetof(struct smb_ace, access_req) > aces_size) break; ace_size = le16_to_cpu(ace->size); if (ace_size > aces_size) break; The first check only requires the 4-byte ACE header to be in bounds; it does not require access_req (4 bytes at offset 4) to be readable. An attacker who has set a crafted DACL on a file they own can declare ace->size == 4 with aces_size == 4, pass both checks, and then granted |= le32_to_cpu(ace->access_req); /* upper loop */ compare_sids(&sid, &ace->sid); /* lower loop */ reads access_req at offset 4 (OOB by up to 4 bytes) and ace->sid at offset 8 (OOB by up to CIFS_SID_BASE_SIZE + SID_MAX_SUB_AUTHORITIES * 4 bytes). Tighten both loops to require ace_size >= offsetof(struct smb_ace, sid) + CIFS_SID_BASE_SIZE which is the smallest valid on-wire ACE layout (4-byte header + 4-byte access_req + 8-byte sid base with zero sub-auths). Also reject ACEs whose sid.num_subauth exceeds SID_MAX_SUB_AUTHORITIES before letting compare_sids() dereference sub_auth[] entries. parse_sec_desc() already enforces an equivalent check (lines 441-448); smb_check_perm_dacl() simply grew weaker validation over time. Reachability: authenticated SMB client with permission to set an ACL on a file. On a subsequent CREATE against that file, the kernel walks the stored DACL via smb_check_perm_dacl() and triggers the OOB read. Not pre-auth, and the OOB read is not reflected to the attacker, but KASAN reports and kernel state corruption are possible.

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

The underlying weakness: Out-of-bounds Write

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

How developers prevent this class of flaw

  • Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
  • Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega, and the Strsafe.h library from Microsoft. These libraries provide safer versions of overflow-prone string-handling functions.
  • Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.

More Out-of-bounds Write vulnerabilities (CWE-787)

Timeline

  1. CVE record published.
  2. Record last changed materially (score, affected products, status or references).

References

Recent Out-of-bounds Write vulnerabilities

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