HighCVE-2026-31712

Linux Kernel: security vulnerability (CVE-2026-31712)

Published 01.05.2026Last modified 15.10.2026Sources: Debian LTS, Ubuntu, Siemens ProductCERT, BSI, CVE.org, EUVD, Msrc Update Guide

What is affected, what to do

Update Linux Kernel to version 5.15.210, Linux Kernel to version 6.1.176, Linux Kernel to version 6.6.140.

Affected: Linux Kernel lt 5.15..5.15.210
Linux Kernel lt 5.16..6.1.176
Linux Kernel lt 6.2..6.6.140
Linux Kernel lt 6.7..6.12.84
Linux Kernel lt 6.13..6.18.25
Linux Kernel lt 6.19..7.0.2
Fixed in: Linux Kernel 5.15.210
Linux Kernel 6.1.176
Linux Kernel 6.6.140
Linux Kernel 6.12.84
Linux Kernel 6.18.25
Linux Kernel 7.0.2
Linux Kernel 7.1

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Metrics

8.3

Priority

XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

Source: NVD, CVSS v3

8.3

CVSS v3

Severity High on the scale from 0 to 10.

Source: Debian LTS, Ubuntu, Siemens ProductCERT, BSI, CVE.org, EUVD, Msrc Update Guide

0.3 %

EPSS score

Low — model estimates < 1% exploitation likelihood.

Source: FIRST EPSS, percentile 25.3

Show all metrics

Severity: High
Priority (0–325) The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first? Read in glossary: 63.47 Methodology
Exploit maturity An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack. Read in glossary: no public PoC known
XIEM Effective CVSS XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command. Read in glossary: 8.3 Methodology
CVSS v3 CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions. Read in glossary: 8.3
EPSS score The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“. Read in glossary: 0.3 %; Low — model estimates < 1% exploitation likelihood.
EPSS percentile The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking. Read in glossary: 25.3; Elevated — this CVE ranks above at least 10% of all CVEs scored today.
KEV status The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching. Read in glossary: —
Published: 01.05.2026

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2 NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management. Read in glossary: High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
CRA The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates. Read in glossary: From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
ISO/IEC 27001 ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security. Read in glossary: Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

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: Debian LTS Advisories, Ubuntu Security Notices, siemens_advisory, BSI WID Portal, BSI CSAF, NVD (NIST), ENISA EUVD, CVE.org (MITRE), cvelistv5, Microsoft Security Update Guide

Affected products

The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

Affected products
		Affected versions	Fixed in
Linux	Linux	`6.2 – < 6.6.140` `6.13 – < 6.18.25` `5.15 – < 5.15.210` `6.7 – < 6.12.84` `—` `6.19 – < 7.0.2` `5.16 – < 6.1.176`	`6.6.140` `6.18.25` `5.15.210` `6.12.84` `7.1` `7.0.2` `6.1.176`
Microsoft	Azure Linux	`azl3`	—
Siemens	SIMATIC S7	`1500 TM MFP V1.1.1 GNU/Linux subsystem`	—

Vendors and products

Affected operating systems

Affected operating systems

Linux	debian	linux	`bookworm`
Linux	debian	linux-6.1	`bullseye`
Linux	ubuntu	linux-gcp-5.15	`focal`
Linux	linux	linux_kernel	—

References & sources

git.kernel.orgstable/c/325d4ac11f526cb8964cff14548ccf02d8c756d8euvd
git.kernel.orgstable/c/95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4ceuvd
git.kernel.orgstable/c/90089584b2e25c4510b7b987387b4405f0673eceeuvd
git.kernel.orgstable/c/151b1799861fde38087c08f613abc2843ef597b0euvd
git.kernel.orgstable/c/d07b26f39246a82399661936dd0c853983cfade7euvd
git.kernel.orgstable/c/282cbbb476b9f35793452bc461934af4c7eca169
git.kernel.orgstable/c/f20adc4ef7428bc485ee83fd1a592252fb87718b
Siemens ProductCERTproductcert/html/ssa-784472.html

Changes to this CVE

Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

15.10.2026Record modifiedLinux

New references:

and 3 more references

Show 18 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://git.kernel.org/stable/c/151b1799861fde38087c08f613abc2843ef597b0
Reference	added	—	https://git.kernel.org/stable/c/282cbbb476b9f35793452bc461934af4c7eca169
Reference	added	—	https://git.kernel.org/stable/c/325d4ac11f526cb8964cff14548ccf02d8c756d8
Reference	added	—	https://git.kernel.org/stable/c/90089584b2e25c4510b7b987387b4405f0673ece
Reference	added	—	https://git.kernel.org/stable/c/95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c
Reference	added	—	https://git.kernel.org/stable/c/d07b26f39246a82399661936dd0c853983cfade7
Reference	added	—	https://git.kernel.org/stable/c/f20adc4ef7428bc485ee83fd1a592252fb87718b
Reference	removed	https://git.kernel.org/stable/c/151b1799861fde38087c08f613abc2843ef597b0	—
Reference	removed	https://git.kernel.org/stable/c/282cbbb476b9f35793452bc461934af4c7eca169	—
Reference	removed	https://git.kernel.org/stable/c/325d4ac11f526cb8964cff14548ccf02d8c756d8	—
Reference	removed	https://git.kernel.org/stable/c/90089584b2e25c4510b7b987387b4405f0673ece	—
Reference	removed	https://git.kernel.org/stable/c/95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c	—
Reference	removed	https://git.kernel.org/stable/c/d07b26f39246a82399661936dd0c853983cfade7	—
Reference	removed	https://git.kernel.org/stable/c/f20adc4ef7428bc485ee83fd1a592252fb87718b	—
Reference type	removed	https://git.kernel.org/stable/c/151b1799861fde38087c08f613abc2843ef597b0 Types: Patch	—
Reference type	removed	https://git.kernel.org/stable/c/90089584b2e25c4510b7b987387b4405f0673ece Types: Patch	—
Reference type	removed	https://git.kernel.org/stable/c/95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c Types: Patch	—
Reference type	removed	https://git.kernel.org/stable/c/d07b26f39246a82399661936dd0c853983cfade7 Types: Patch	—

Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

15.10.2026Record modifiedSiemens ADP

New references:

https://cert-portal.siemens.com/productcert/html/ssa-784472.html

Show 2 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Affected versions (publisher)	added	—	New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/31xxx/CVE-2026-31712.json">CVE-2026-31712</a>
Reference	added	—	https://cert-portal.siemens.com/productcert/html/ssa-784472.html

Source identifier: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e

19.06.2026Record modifiedLinux

New references:

Show 3 original changes

Individual changes of this event as published by NVD
Type	Action	Before	After
Reference	added	—	https://git.kernel.org/stable/c/282cbbb476b9f35793452bc461934af4c7eca169
Reference	added	—	https://git.kernel.org/stable/c/f20adc4ef7428bc485ee83fd1a592252fb87718b
Affected versions (publisher)	changed	Linux, Linux	Linux, Linux

Source identifier: 416baaa9-dc9f-4396-8d5f-8c081fb06d67

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