HighCVE-2025-21756

    Linux Kernel: Use-After-Free (CVE-2025-21756)

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

    What is affected, what to do

    A flaw was found in the Linux kernel's virtual socket protocol network driver, where an improperly timed socket unbinding could result in a use-after-free issue. This flaw allows an attacker who can create and destroy arbitrary connections on virtual connections to read or modify system memory, potentially leading to an escalation of privileges or the compromise of sensitive data.

    The vulnerability is being actively exploited; treat it as a priority. Update Linux Kernel to version 5.10.235, Linux Kernel to version 5.15.179, Linux Kernel to version 6.1.131.

    Affected
    • Linux Kernel lt 5.5..5.10.235
    • Linux Kernel lt 5.11..5.15.179
    • Linux Kernel lt 5.16..6.1.131
    • 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 5.10.235
    • Linux Kernel 5.15.179
    • Linux Kernel 6.1.131
    • 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

    7.8

    Priority

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

    Source: NVD, CVSS v3

    7.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Siemens ProductCERT, Red Hat, SUSE, BSI, Debian LTS, Debian, CVE.org, Msrc Update Guide, OSV, EUVD

    0.9 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 59.4

    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
    75.18 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
    actively exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
    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
    7.8 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
    7.8
    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
    0.9 %
    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
    59.4
    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: proof of concept · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 14 August 2025
    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-416

    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
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    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
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    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

    A flaw was found in the Linux kernel's virtual socket protocol network driver, where an improperly timed socket unbinding could result in a use-after-free issue. This flaw allows an attacker who can create and destroy arbitrary connections on virtual connections to read or modify system memory, potentially leading to an escalation of privileges or the compromise of sensitive data.

    Source: siemens_advisory, redhat_csaf, suse_csaf, BSI CSAF, BSI WID Portal, Debian LTS Advisories, Debian Security Advisories, cvelistv5, Microsoft Security Update Guide, OSV (Open Source Vulnerabilities), 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 – < 6.1.131
    • —
    • 5.11 – < 5.15.179
    • 6.2 – < 6.6.79
    • 6.13 – < 6.13.4
    • 6.7 – < 6.12.16
    • 5.10.235
    • 6.1.131
    • 6.14
    • 5.15.179
    • 6.6.79
    • 6.13.4
    • 6.12.16
    DellSecure Connect Gateway
    • < 5.30.0.14
    • 5.30.0.14
    SiemensSIMATIC S7
    • 1500 TM MFP V1.1.1 GNU/Linux subsystem
    • —
    android:linux_kernel:
    • Kernel
    • :0
    • —
    • :2025-09-05

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbookworm
    Linuxdebianlinuxbullseye
    Linuxdebianlinux-6.1bullseye
    Linuxlinuxlinux_kernel—

    Weakness classes (CWE)

    • CWE-416Use After Free

      Variant

      The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

      Entry at MITRE CWE-416

    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 21 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/3f43540166128951cc1be7ab1ce6b7f05c670d8b
      Referenceadded
      —
      https://git.kernel.org/stable/c/42b33381e5e1f2b967dc4fb4221ddb9aaf10d197
      Referenceadded
      —
      https://git.kernel.org/stable/c/645ce25aa0e67895b11d89f27bb86c9d444c40f8
      Referenceadded
      —
      https://git.kernel.org/stable/c/b1afd40321f1c243cffbcf40ea7ca41aca87fa5e
      Referenceadded
      —
      https://git.kernel.org/stable/c/e48fcb403c2d0e574c19683f09399ab4cf67809c
      Referenceadded
      —
      https://git.kernel.org/stable/c/e7754d564579a5db9c5c9f74228df5d6dd6f1173
      Referenceadded
      —
      https://git.kernel.org/stable/c/fcdd2242c0231032fc84e1404315c245ae56322a
      Referenceremoved
      https://git.kernel.org/stable/c/3f43540166128951cc1be7ab1ce6b7f05c670d8b
      —
      Referenceremoved
      https://git.kernel.org/stable/c/42b33381e5e1f2b967dc4fb4221ddb9aaf10d197
      —
      Referenceremoved
      https://git.kernel.org/stable/c/645ce25aa0e67895b11d89f27bb86c9d444c40f8
      —
      Referenceremoved
      https://git.kernel.org/stable/c/b1afd40321f1c243cffbcf40ea7ca41aca87fa5e
      —
      Referenceremoved
      https://git.kernel.org/stable/c/e48fcb403c2d0e574c19683f09399ab4cf67809c
      —
      Referenceremoved
      https://git.kernel.org/stable/c/e7754d564579a5db9c5c9f74228df5d6dd6f1173
      —
      Referenceremoved
      https://git.kernel.org/stable/c/fcdd2242c0231032fc84e1404315c245ae56322a
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/3f43540166128951cc1be7ab1ce6b7f05c670d8b Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/42b33381e5e1f2b967dc4fb4221ddb9aaf10d197 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/645ce25aa0e67895b11d89f27bb86c9d444c40f8 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/b1afd40321f1c243cffbcf40ea7ca41aca87fa5e Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/e48fcb403c2d0e574c19683f09399ab4cf67809c Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/e7754d564579a5db9c5c9f74228df5d6dd6f1173 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/fcdd2242c0231032fc84e1404315c245ae56322a 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/2025/05/msg00030.html
      Referenceadded
      —
      https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html
      Referenceremoved
      https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
      —
      Referenceremoved
      https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html
      —

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

    3. Record modifiedSiemens ADP

      Show 6 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-2025-21756.json">CVE-2025-21756</a>
      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-784472.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

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