CriticalCVE-2026-31705

    Linux Kernel: Out-of-Bounds Write (CVE-2026-31705)

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

    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix out-of-bounds write in smb2_get_ea() EA alignment smb2_get_ea() applies 4-byte alignment padding via memset() after writing each EA entry. The bounds check on buf_free_len is performed before the value memcpy, but the alignment memset fires unconditionally afterward with no check on remaining space.

    Update Linux Kernel to version 6.1.175, Linux Kernel to version 5.16, Linux Kernel to version 6.6.136.

    Affected
    • Linux Kernel lt 6.1.71..6.1.175
    • Linux Kernel lt 5.15.145..5.16
    • Linux Kernel lt 6.6..6.6.136
    • 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 6.1.175
    • Linux Kernel 5.16
    • Linux Kernel 6.6.136
    • Linux Kernel 6.12.84
    • Linux Kernel 6.18.25
    • Linux Kernel 7.0.2
    • Linux Kernel 7.1

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    Metrics

    9.8

    Priority

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

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

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

    0.4 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 33.8

    Show all metrics
    Severity
    Critical
    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
    75.06 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
    9.8 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
    9.8
    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
    0.4 %
    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
    33.8
    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

    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: fix out-of-bounds write in smb2_get_ea() EA alignment smb2_get_ea() applies 4-byte alignment padding via memset() after writing each EA entry. The bounds check on buf_free_len is performed before the value memcpy, but the alignment memset fires unconditionally afterward with no check on remaining space. When the EA value exactly fills the remaining buffer (buf_free_len == 0 after value subtraction), the alignment memset writes 1-3 NUL bytes past the buf_free_len boundary. In compound requests where the response buffer is shared across commands, the first command (e.g., READ) can consume most of the buffer, leaving a tight remainder for the QUERY_INFO EA response. The alignment memset then overwrites past the physical kvmalloc allocation into adjacent kernel heap memory. Add a bounds check before the alignment memset to ensure buf_free_len can accommodate the padding bytes. This is the same bug pattern fixed by commit beef2634f81f ("ksmbd: fix potencial OOB in get_file_all_info() for compound requests") and commit fda9522ed6af ("ksmbd: fix OOB write in QUERY_INFO for compound requests"), both of which added bounds checks before unconditional writes in QUERY_INFO response handlers.

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

    Affected products

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

    Affected products
    Affected versionsFixed in
    LinuxLinux
    • 5.15.145 – < 5.16
    • 6.6 – < 6.6.136
    • 6.13 – < 6.18.25
    • 6.7 – < 6.12.84
    • —
    • 6.19 – < 7.0.2
    • 6.1.71 – < 6.1.175
    • 5.16
    • 6.6.136
    • 6.18.25
    • 6.12.84
    • 7.1
    • 7.0.2
    • 6.1.175
    MicrosoftAzure Linux
    • azl3
    • —
    SiemensSIMATIC S7
    • 1500 TM MFP V1.1.1 GNU/Linux subsystem
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxubuntuawsbionic
    Linuxubuntuawsjammy
    Linuxubuntuawsnoble
    Linuxubuntuawsresolute
    Linuxubuntuawsxenial
    Linuxubuntuaws-6.8jammy
    Linuxubuntuaws-hwexenial
    Linuxubuntuazurejammy
    Linuxubuntuazurenoble
    Linuxubuntuazureresolute
    Linuxubuntuazurexenial
    Linuxubuntuazure-4.15bionic
    Linuxubuntugcpjammy
    Linuxubuntugcpnoble
    Linuxubuntugcpresolute
    Linuxubuntugcpxenial
    Linuxubuntugcp-4.15bionic
    Linuxubuntugcp-6.8jammy
    Linuxubuntugeneric-4.15bionic
    Linuxubuntugeneric-4.15xenial
    Linuxubuntugeneric-4.4xenial
    Linuxubuntugeneric-5.4bionic
    Linuxubuntugeneric-5.4focal
    Linuxubuntugkejammy

    References & sources

    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).

    1. Record modifiedLinux

      Show 17 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/30010c952077a1c89ecdd71fc4d574c75a8f5617
      Referenceadded
      —
      https://git.kernel.org/stable/c/790304c02bf9bd7b8171feda4294d6e62d32ae8f
      Referenceadded
      —
      https://git.kernel.org/stable/c/922d48fe8c19f388ffa2f709f33acaae4e408de2
      Referenceadded
      —
      https://git.kernel.org/stable/c/98f3de6ef4efbd899348d333f0902dc4ff14380c
      Referenceadded
      —
      https://git.kernel.org/stable/c/ddbbc8b2a09dd2cfed90871313e3691ae1db08a2
      Referenceadded
      —
      https://git.kernel.org/stable/c/ffbce350c6fd1e99116ea57383b9031717e36d3b
      Referenceremoved
      https://git.kernel.org/stable/c/30010c952077a1c89ecdd71fc4d574c75a8f5617
      —
      Referenceremoved
      https://git.kernel.org/stable/c/790304c02bf9bd7b8171feda4294d6e62d32ae8f
      —
      Referenceremoved
      https://git.kernel.org/stable/c/922d48fe8c19f388ffa2f709f33acaae4e408de2
      —
      Referenceremoved
      https://git.kernel.org/stable/c/98f3de6ef4efbd899348d333f0902dc4ff14380c
      —
      Referenceremoved
      https://git.kernel.org/stable/c/ddbbc8b2a09dd2cfed90871313e3691ae1db08a2
      —
      Referenceremoved
      https://git.kernel.org/stable/c/ffbce350c6fd1e99116ea57383b9031717e36d3b
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/30010c952077a1c89ecdd71fc4d574c75a8f5617 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/790304c02bf9bd7b8171feda4294d6e62d32ae8f Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/922d48fe8c19f388ffa2f709f33acaae4e408de2 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/98f3de6ef4efbd899348d333f0902dc4ff14380c Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/ffbce350c6fd1e99116ea57383b9031717e36d3b Types: Patch
      —

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

    2. Record modifiedSiemens ADP

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/31xxx/CVE-2026-31705.json">CVE-2026-31705</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-784472.html

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

    Linked advisories

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