HighCVE-2025-21765

    Linux Kernel: security vulnerability (CVE-2025-21765)

    Published Last modified Sources: Siemens ProductCERT, BSI, SUSE, Debian LTS, Red Hat, CVE.org, EUVD

    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: ipv6: use RCU protection in ip6_default_advmss() ip6_default_advmss() needs rcu protection to make sure the net structure it reads does not disappear.

    Update Linux Kernel to version 5.4.291, Linux Kernel to version 5.10.235, Linux Kernel to version 5.15.179.

    Affected
    • Linux Kernel lt 2.6.26..5.4.291
    • Linux Kernel lt 5.5..5.10.235
    • Linux Kernel lt 5.11..5.15.179
    • Linux Kernel lt 5.16..6.1.129
    • Linux Kernel lt 6.2..6.6.79
    • Linux Kernel lt 6.7..6.12.16
    • Linux Kernel lt 6.13..6.13.4
    Fixed in
    • Linux Kernel 5.4.291
    • Linux Kernel 5.10.235
    • Linux Kernel 5.15.179
    • Linux Kernel 6.1.129
    • Linux Kernel 6.6.79
    • Linux Kernel 6.12.16
    • Linux Kernel 6.13.4
    • Linux Kernel 6.14

    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: Vendor (CNA), CVSS v3

    8.1

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Siemens ProductCERT, BSI, SUSE, Debian LTS, Red Hat, CVE.org, EUVD

    0.6 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 49.3

    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
    67.91 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“.

    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
    49.3
    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

    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: ipv6: use RCU protection in ip6_default_advmss() ip6_default_advmss() needs rcu protection to make sure the net structure it reads does not disappear.

    Source: siemens_advisory, BSI WID Portal, BSI CSAF, suse_csaf, Debian LTS Advisories, redhat_csaf, cvelistv5, NVD (NIST), CVE.org (MITRE), ENISA EUVD

    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
    • 5.5 – < 5.10.235
    • —
    • 5.16 – < 6.1.129
    • 5.11 – < 5.15.179
    • 6.2 – < 6.6.79
    • 2.6.26 – < 5.4.291
    • 6.13 – < 6.13.4
    • 6.7 – < 6.12.16
    • 5.10.235
    • 6.14
    • 6.1.129
    • 5.15.179
    • 6.6.79
    • 5.4.291
    • 6.13.4
    • 6.12.16
    DellSecure Connect Gateway
    • < 5.30.0.14
    • 5.30.0.14
    IBMSecurity Verify Access
    • < 10.0.9.2
    • 10.0.9.2
    SiemensSIMATIC S7
    • 1500 TM MFP V1.1.1 GNU/Linux subsystem
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbullseye
    Linuxdebianlinux-6.1bullseye
    Linuxlinuxlinux_kernel6.14
    Linuxlinuxlinux_kernel—

    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 24 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/28de355b63ad42309ed5a03ee7c436c90512265b
      Referenceadded
      —
      https://git.kernel.org/stable/c/3c8ffcd248da34fc41e52a46e51505900115fc2a
      Referenceadded
      —
      https://git.kernel.org/stable/c/4176a68b0db8fc74ac14fcd00ba8231371051dc2
      Referenceadded
      —
      https://git.kernel.org/stable/c/550ed693f47370502a71b85382e7f9e6417300b8
      Referenceadded
      —
      https://git.kernel.org/stable/c/713a40c892f40300d63691d9f85b2a23b48fe1e8
      Referenceadded
      —
      https://git.kernel.org/stable/c/78ad057472d8c76e0602402269222f9f9c698790
      Referenceadded
      —
      https://git.kernel.org/stable/c/84212387caadb211cd9dadd6fd5563bd37dc1f5e
      Referenceadded
      —
      https://git.kernel.org/stable/c/d02f30d220ef9511568a48dba8a9004c65f8d904
      Referenceremoved
      https://git.kernel.org/stable/c/28de355b63ad42309ed5a03ee7c436c90512265b
      —
      Referenceremoved
      https://git.kernel.org/stable/c/3c8ffcd248da34fc41e52a46e51505900115fc2a
      —
      Referenceremoved
      https://git.kernel.org/stable/c/4176a68b0db8fc74ac14fcd00ba8231371051dc2
      —
      Referenceremoved
      https://git.kernel.org/stable/c/550ed693f47370502a71b85382e7f9e6417300b8
      —
      Referenceremoved
      https://git.kernel.org/stable/c/713a40c892f40300d63691d9f85b2a23b48fe1e8
      —
      Referenceremoved
      https://git.kernel.org/stable/c/78ad057472d8c76e0602402269222f9f9c698790
      —
      Referenceremoved
      https://git.kernel.org/stable/c/84212387caadb211cd9dadd6fd5563bd37dc1f5e
      —
      Referenceremoved
      https://git.kernel.org/stable/c/d02f30d220ef9511568a48dba8a9004c65f8d904
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/28de355b63ad42309ed5a03ee7c436c90512265b Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/3c8ffcd248da34fc41e52a46e51505900115fc2a Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/4176a68b0db8fc74ac14fcd00ba8231371051dc2 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/550ed693f47370502a71b85382e7f9e6417300b8 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/713a40c892f40300d63691d9f85b2a23b48fe1e8 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/78ad057472d8c76e0602402269222f9f9c698790 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/84212387caadb211cd9dadd6fd5563bd37dc1f5e Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/d02f30d220ef9511568a48dba8a9004c65f8d904 Types: Patch
      —

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

    2. Record modifiedCVE Program

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html
      Referenceadded
      —
      https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
      Referenceremoved
      https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html
      —
      Referenceremoved
      https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
      —

      Source identifier: af854a3a-2127-422b-91ae-364da2661108

    3. Record modifiedSiemens ADP

      Show 9 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2025/21xxx/CVE-2025-21765.json">CVE-2025-21765</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-019113.html
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-082556.html
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-265688.html
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-457936.html
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-784472.html
      Referenceremoved
      https://cert-portal.siemens.com/productcert/html/ssa-019113.html
      —
      Referenceremoved
      https://cert-portal.siemens.com/productcert/html/ssa-082556.html
      —
      Referenceremoved
      https://cert-portal.siemens.com/productcert/html/ssa-265688.html
      —

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

    4. Record modifiedLinux

      CVSS V3.1: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

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

    Embed badge

    Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

    Badge preview for CVE-2025-21765
    <a href="https://intel.neosec.eu/en/cve/CVE-2025-21765"><img src="https://intel.neosec.eu/badge/cve/CVE-2025-21765.svg?lang=en" alt="CVE-2025-21765 – NEOSEC Intel" height="20"></a>