HighCVE-2025-21795

    Linux Kernel: security vulnerability (CVE-2025-21795)

    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: NFSD: fix hang in nfsd4_shutdown_callback If nfs4_client is in courtesy state then there is no point to send the callback. This causes nfsd4_shutdown_callback to hang since cl_cb_inflight is not 0. This hang lasts about 15 minutes until TCP notifies NFSD that the connection was dropped.

    Update Linux Kernel to version 5.10.235, Linux Kernel to version 5.15.179, Linux Kernel to version 6.1.129.

    Affected
    • Linux Kernel lt 5.10.220..5.10.235
    • Linux Kernel lt 5.15.154..5.15.179
    • Linux Kernel lt 5.19..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 5.10.235
    • 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

    7.5

    Priority

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

    Source: Vendor (CNA), CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

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

    0.7 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 51.9

    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
    67.05 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
    7.5 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
    7.5
    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
    0.7 %
    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
    51.9
    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: NFSD: fix hang in nfsd4_shutdown_callback If nfs4_client is in courtesy state then there is no point to send the callback. This causes nfsd4_shutdown_callback to hang since cl_cb_inflight is not 0. This hang lasts about 15 minutes until TCP notifies NFSD that the connection was dropped. This patch modifies nfsd4_run_cb_work to skip the RPC call if nfs4_client is in courtesy state.

    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
    • —
    • 5.19 – < 6.1.129
    • 6.2 – < 6.6.79
    • 6.13 – < 6.13.4
    • 5.10.220 – < 5.10.235
    • 5.15.154 – < 5.15.179
    • 6.7 – < 6.12.16
    • 6.14
    • 6.1.129
    • 6.6.79
    • 6.13.4
    • 5.10.235
    • 5.15.179
    • 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 21 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/036ac2778f7b28885814c6fbc07e156ad1624d03
      Referenceadded
      —
      https://git.kernel.org/stable/c/23ad7797c74cd8f7f90617f1e59a8703e2b43908
      Referenceadded
      —
      https://git.kernel.org/stable/c/38d345f612503b850c2973e5a879f88e441b34d7
      Referenceadded
      —
      https://git.kernel.org/stable/c/abed68027ea3ab893ac85cc46a00e2e64a324239
      Referenceadded
      —
      https://git.kernel.org/stable/c/cedfbb92cf97a6bff3d25633001d9c44442ee854
      Referenceadded
      —
      https://git.kernel.org/stable/c/e88d2451cd42e025465d6b51fd716a47b0b3800d
      Referenceadded
      —
      https://git.kernel.org/stable/c/efa8a261c575f816c7e79a87aeb3ef8a0bd6b221
      Referenceremoved
      https://git.kernel.org/stable/c/036ac2778f7b28885814c6fbc07e156ad1624d03
      —
      Referenceremoved
      https://git.kernel.org/stable/c/23ad7797c74cd8f7f90617f1e59a8703e2b43908
      —
      Referenceremoved
      https://git.kernel.org/stable/c/38d345f612503b850c2973e5a879f88e441b34d7
      —
      Referenceremoved
      https://git.kernel.org/stable/c/abed68027ea3ab893ac85cc46a00e2e64a324239
      —
      Referenceremoved
      https://git.kernel.org/stable/c/cedfbb92cf97a6bff3d25633001d9c44442ee854
      —
      Referenceremoved
      https://git.kernel.org/stable/c/e88d2451cd42e025465d6b51fd716a47b0b3800d
      —
      Referenceremoved
      https://git.kernel.org/stable/c/efa8a261c575f816c7e79a87aeb3ef8a0bd6b221
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/036ac2778f7b28885814c6fbc07e156ad1624d03 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/23ad7797c74cd8f7f90617f1e59a8703e2b43908 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/38d345f612503b850c2973e5a879f88e441b34d7 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/abed68027ea3ab893ac85cc46a00e2e64a324239 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/cedfbb92cf97a6bff3d25633001d9c44442ee854 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/e88d2451cd42e025465d6b51fd716a47b0b3800d Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/efa8a261c575f816c7e79a87aeb3ef8a0bd6b221 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-2025-21795.json">CVE-2025-21795</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:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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

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

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