CriticalCVE-2026-31637

    Linux Kernel: security vulnerability (CVE-2026-31637)

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

    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: rxrpc: reject undecryptable rxkad response tickets rxkad_decrypt_ticket() decrypts the RXKAD response ticket and then parses the buffer as plaintext without checking whether crypto_skcipher_decrypt() succeeded. A malformed RESPONSE can therefore use a non-block-aligned ticket length, make the decrypt operation fail, and still drive the ticket parser with attacker-controlled bytes.

    Update Linux Kernel to version 5.10.258, Linux Kernel to version 5.15.209, Linux Kernel to version 6.1.175.

    Affected
    • Linux Kernel lt 2.6.22..5.10.258
    • Linux Kernel lt 5.11..5.15.209
    • Linux Kernel lt 5.16..6.1.175
    • Linux Kernel lt 6.2..6.6.135
    • Linux Kernel lt 6.7..6.12.82
    • Linux Kernel lt 6.13..6.18.23
    • Linux Kernel lt 6.19..6.19.13
    • Linux Kernel lt 6.20..7.0
    Fixed in
    • Linux Kernel 5.10.258
    • Linux Kernel 5.15.209
    • Linux Kernel 6.1.175
    • Linux Kernel 6.6.135
    • Linux Kernel 6.12.82
    • Linux Kernel 6.18.23
    • Linux Kernel 6.19.13
    • Linux Kernel 7.0

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

    Metrics

    9.8

    Priority

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

    Source: Vendor (CNA), CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

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

    0.6 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 48.2

    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
    84.14 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
    0.6 %
    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
    48.2
    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
    CISA assessment (SSVC)
    Exploitation: none known · automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 16 October 2026
    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-754

    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: rxrpc: reject undecryptable rxkad response tickets rxkad_decrypt_ticket() decrypts the RXKAD response ticket and then parses the buffer as plaintext without checking whether crypto_skcipher_decrypt() succeeded. A malformed RESPONSE can therefore use a non-block-aligned ticket length, make the decrypt operation fail, and still drive the ticket parser with attacker-controlled bytes. Check the decrypt result and abort the connection with RXKADBADTICKET when ticket decryption fails.

    Source: Ubuntu Security Notices, Debian Security Advisories, Debian LTS Advisories, siemens_advisory, cvelistv5, NVD (NIST), ENISA EUVD, CVE.org (MITRE), Microsoft Security Update Guide, 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
    • 5.16 – < 6.1.175
    • 2.6.22 – < 5.10.258
    • 6.7 – < 6.12.82
    • 6.2 – < 6.6.135
    • 5.11 – < 5.15.209
    • 6.13 – < 6.18.23
    • 6.19 – < 6.19.13
    • 6.20 – < 7.0
    • 6.1.175
    • 5.10.258
    • 6.12.82
    • 6.6.135
    • 5.15.209
    • 6.18.23
    • 6.19.13
    • 7.0
    SiemensSIMATIC S7
    • 1500 TM MFP V1.1.1 GNU/Linux subsystem
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbookworm
    Linuxdebianlinuxbullseye
    Linuxdebianlinuxtrixie
    Linuxdebianlinux-6.1bullseye
    Linuxlinuxlinux_kernel2.6.22
    Linuxlinuxlinux_kernel7.0
    Linuxlinuxlinux_kernel—

    Weakness classes (CWE)

    • CWE-754Improper Check for Unusual or Exceptional Conditions

      Class

      The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.

      Entry at MITRE CWE-754

    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 modifiedCISA ADP

      Weakness type: CWE-754

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Weakness type (CWE)added
      —
      CWE-754

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: yes

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-31637","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:11:24.761157Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    3. Record modifiedLinux

      Show 21 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/22f6258e7b31dba9bf88dce4e3ee7f0f20072e60
      Referenceadded
      —
      https://git.kernel.org/stable/c/252157d939d179b5d767cb860ff8fa7f8723b67a
      Referenceadded
      —
      https://git.kernel.org/stable/c/47073aab8a3a5a7b41c9bd37d2a3dcbeeccd6c8a
      Referenceadded
      —
      https://git.kernel.org/stable/c/58fcd1b156152613ba00a064a129fb69507ddd7d
      Referenceadded
      —
      https://git.kernel.org/stable/c/a149dcae23309df9de1c3b6b5d468610ef5ab7de
      Referenceadded
      —
      https://git.kernel.org/stable/c/a75b3b361dd481d942c5f259a82d59718a41092c
      Referenceadded
      —
      https://git.kernel.org/stable/c/b3a808cd0790b5075aaa2bc3588edf02cd71d352
      Referenceadded
      —
      https://git.kernel.org/stable/c/fe4447cd95623b1cfacc15f280aab73a6d7340b2
      Referenceremoved
      https://git.kernel.org/stable/c/22f6258e7b31dba9bf88dce4e3ee7f0f20072e60
      —
      Referenceremoved
      https://git.kernel.org/stable/c/252157d939d179b5d767cb860ff8fa7f8723b67a
      —
      Referenceremoved
      https://git.kernel.org/stable/c/47073aab8a3a5a7b41c9bd37d2a3dcbeeccd6c8a
      —
      Referenceremoved
      https://git.kernel.org/stable/c/58fcd1b156152613ba00a064a129fb69507ddd7d
      —
      Referenceremoved
      https://git.kernel.org/stable/c/a149dcae23309df9de1c3b6b5d468610ef5ab7de
      —
      Referenceremoved
      https://git.kernel.org/stable/c/a75b3b361dd481d942c5f259a82d59718a41092c
      —
      Referenceremoved
      https://git.kernel.org/stable/c/b3a808cd0790b5075aaa2bc3588edf02cd71d352
      —
      Referenceremoved
      https://git.kernel.org/stable/c/fe4447cd95623b1cfacc15f280aab73a6d7340b2
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/22f6258e7b31dba9bf88dce4e3ee7f0f20072e60 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/47073aab8a3a5a7b41c9bd37d2a3dcbeeccd6c8a Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/58fcd1b156152613ba00a064a129fb69507ddd7d Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/a149dcae23309df9de1c3b6b5d468610ef5ab7de Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/fe4447cd95623b1cfacc15f280aab73a6d7340b2 Types: Patch
      —

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

    4. 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-2026-31637.json">CVE-2026-31637</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-784472.html

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

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