HighCVE-2026-63909

    Linux Kernel: Out-of-bounds Read (CVE-2026-63909)

    Published Last modified Sources: Ubuntu, CVE.org, BSI

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    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops Commit d07b26f39246 ("ksmbd: require minimum ACE size in smb_check_perm_dacl()") introduced a transposed bounds check: if (offsetof(struct smb_ace, sid) + aces_size < CIFS_SID_BASE_SIZE) Since offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates to `aces_size < 0`. Because `aces_size` is always non-negative, this check becomes dead code and never breaks the loop.

    Update Linux Kernel to version 6.6.143, Linux Kernel to version 6.12.93, Linux Kernel to version 6.18.35.

    Affected
    • Linux Kernel lt 6.6.140..6.6.143
    • Linux Kernel lt 6.12.84..6.12.93
    • Linux Kernel lt 6.18.25..6.18.35
    • Linux Kernel lt 7.0.2..7.0.12
    Fixed in
    • Linux Kernel 6.6.143
    • Linux Kernel 6.12.93
    • Linux Kernel 6.18.35
    • Linux Kernel 7.0.12

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    8.1

    Priority

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

    Source: NVD, CVSS v3

    8.1

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Ubuntu, CVE.org, BSI

    0.6 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 50.2

    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
    81.31 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
    8.1 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
    8.1
    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“.

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    0.6 %
    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
    50.2
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    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
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-125

    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: OOB read regression in smb_check_perm_dacl() ACE-walk loops Commit d07b26f39246 ("ksmbd: require minimum ACE size in smb_check_perm_dacl()") introduced a transposed bounds check: if (offsetof(struct smb_ace, sid) + aces_size < CIFS_SID_BASE_SIZE) Since offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates to `aces_size < 0`. Because `aces_size` is always non-negative, this check becomes dead code and never breaks the loop. Worse, that commit removed the old 4-byte guard, meaning the loop now reads `ace->size` (offset 2) even when `aces_size` is 0-3 bytes. This re-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation during subsequent SMB2_CREATE operations. Fix this by properly transposing the comparison to require at least 16 bytes (8-byte offset + 8-byte SID base), matching the correct form used in smb_inherit_dacl().

    Source: Ubuntu Security Notices, NVD (NIST), cvelistv5, 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
    • 6.12.84 – < 6.12.93
    • 7.0.2 – < 7.0.12
    • 6.18.25 – < 6.18.35
    • 6.6.140 – < 6.6.143
    • 6.12.93
    • 7.0.12
    • 6.18.35
    • 6.6.143

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxubuntulinuxnoble
    Linuxubuntulinux-awsnoble
    Linuxubuntulinux-aws-6.8jammy
    Linuxubuntulinux-aws-fipsnoble
    Linuxubuntulinux-azurenoble
    Linuxubuntulinux-azure-6.8jammy
    Linuxubuntulinux-azure-fdenoble
    Linuxubuntulinux-azure-fde-6.8jammy
    Linuxubuntulinux-azure-fipsnoble
    Linuxubuntulinux-fipsnoble
    Linuxubuntulinux-gcpnoble
    Linuxubuntulinux-gcp-6.8jammy
    Linuxubuntulinux-gcp-fipsnoble
    Linuxubuntulinux-gkenoble
    Linuxubuntulinux-gkeopnoble
    Linuxubuntulinux-ibmnoble
    Linuxubuntulinux-ibm-6.8jammy
    Linuxubuntulinux-lowlatencynoble
    Linuxubuntulinux-lowlatency-hwe-6.8jammy
    Linuxubuntulinux-nvidianoble
    Linuxubuntulinux-nvidia-6.8jammy
    Linuxubuntulinux-nvidia-lowlatencynoble
    Linuxubuntulinux-oraclenoble
    Linuxubuntulinux-realtimenoble

    Weakness classes (CWE)

    • CWE-125Out-of-bounds Read

      Base

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

      Entry at MITRE CWE-125

    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. Initial analysis by NVDNVD

      Newly listed as affected:
      • Linux Kernel (6.6.140 – before 6.6.143; 6.12.84 – before 6.12.93; 6.18.25 – before 6.18.35; 7.0.2 – before 7.0.12; 5 individual versions)

      Weakness type: CWE-125

      Show 9 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Weakness type (CWE)added
      —
      CWE-125
      Product configurationadded
      —
      OR *cpe:2.3:o:linux:linux_kernel:7.1:rc1:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:7.1:rc2:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:7.1:rc3:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:7.1:rc4:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:7.1:rc5:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.6.140 up to (excluding) 6.6.143 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.12.84 up to (excluding) 6.12.93 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.18.25 up to (excluding) 6.18.35 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 7.0.2 up to (excluding) 7.0.12
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/0e60dafe97eca61721f3db456f97d97a80c6c8ae Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/0fe08c5776a798f46df1fd74b331be26bdd644d6 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/4f7c131d2bdd7cd64b96f60d10be5ea72253f520 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/5500ba1d410aed1eded3eb04a76b10cfb4409334 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/94215d55b09445993929f4fc966061d61de74929 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/d333af32e4451285e427f2d9c29de3a39f6f6d48 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/f6324b4240cf0b26a84c33f68a1222d727ff4af2 Types: Patch

      Source identifier: nvd@nist.gov

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