MediumCVE-2026-53349

    Linux Kernel: security vulnerability (CVE-2026-53349)

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

    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_conntrack: destroy stale expectfn expectations on unregister NAT helpers such as nf_nat_h323 store a raw pointer to module text in exp->expectfn (e.g. ip_nat_q931_expect). nf_ct_helper_expectfn_unregister() only unlinks the callback descriptor and never walks the expectation table, so an expectation pending at module removal survives with a dangling exp->expectfn into freed module text. When the expected connection arrives, init_conntrack() invokes exp->expectfn(), now a stale pointer into the unloaded module.

    Update Linux Kernel to version 6.1.176, Linux Kernel to version 6.6.143, Linux Kernel to version 6.12.94.

    Affected
    • Linux Kernel lt 2.6.20..6.1.176
    • Linux Kernel lt 6.2..6.6.143
    • Linux Kernel lt 6.7..6.12.94
    • Linux Kernel lt 6.13..6.18.36
    • Linux Kernel lt 6.19..7.0.13
    Fixed in
    • Linux Kernel 6.1.176
    • Linux Kernel 6.6.143
    • Linux Kernel 6.12.94
    • Linux Kernel 6.18.36
    • Linux Kernel 7.0.13
    • Linux Kernel 7.1

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

    Metrics

    5.5

    Priority

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

    Source: NVD, CVSS v3

    5.5

    CVSS v3

    Severity Medium on the scale from 0 to 10.

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

    0.1 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 1.9

    Show all metrics
    Severity
    Medium
    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
    47.36 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
    5.5 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
    5.5
    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
    0.1 %
    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
    1.9
    Low — this CVE sits in the lower 10% of all CVEs scored today.
    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
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    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: netfilter: nf_conntrack: destroy stale expectfn expectations on unregister NAT helpers such as nf_nat_h323 store a raw pointer to module text in exp->expectfn (e.g. ip_nat_q931_expect). nf_ct_helper_expectfn_unregister() only unlinks the callback descriptor and never walks the expectation table, so an expectation pending at module removal survives with a dangling exp->expectfn into freed module text. When the expected connection arrives, init_conntrack() invokes exp->expectfn(), now a stale pointer into the unloaded module. Reproduced on a KASAN build by loading the H.323 helpers, creating a Q.931 expectation, unloading nf_nat_h323, then connecting to the expected port: Oops: int3: 0000 [#1] SMP KASAN NOPTI RIP: 0010:0xffffffffa06102d1 init_conntrack.isra.0 (net/netfilter/nf_conntrack_core.c:1862) nf_conntrack_in (net/netfilter/nf_conntrack_core.c:2049) ipv4_conntrack_local (net/netfilter/nf_conntrack_proto.c:223) nf_hook_slow (net/netfilter/core.c:619) __ip_local_out (net/ipv4/ip_output.c:120) __tcp_transmit_skb (net/ipv4/tcp_output.c:1715) tcp_connect (net/ipv4/tcp_output.c:4374) tcp_v4_connect (net/ipv4/tcp_ipv4.c:345) __sys_connect (net/socket.c:2167) Modules linked in: nf_conntrack_h323 [last unloaded: nf_nat_h323] Reaching the dangling state requires CAP_SYS_MODULE in the initial user namespace to remove a NAT helper that still has live expectations, so this is a robustness fix; leaving an expectation pointing at freed text is wrong regardless. Add nf_ct_helper_expectfn_destroy(), which walks the expectation table and drops every expectation whose ->expectfn matches the descriptor being torn down. Call it from each NAT helper's exit path after the existing RCU grace period, so no expectation outlives the code it points at and no extra synchronize_rcu() is introduced. With the fix, the same reproducer runs to completion without the Oops.

    Source: Debian LTS Advisories, Ubuntu Security Notices, siemens_advisory, BSI WID Portal, BSI CSAF, cvelistv5, NVD (NIST), Microsoft Security Update Guide

    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
    • 2.6.20 – < 6.1.176
    • 6.7 – < 6.12.94
    • 6.13 – < 6.18.36
    • —
    • 6.19 – < 7.0.13
    • 6.2 – < 6.6.143
    • 6.1.176
    • 6.12.94
    • 6.18.36
    • 7.1
    • 7.0.13
    • 6.6.143
    SiemensSIMATIC S7
    • 1500 TM MFP V1.1.1 GNU/Linux subsystem
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbookworm
    Linuxdebianlinux-6.1bullseye
    Linuxubuntulinux-oracle-7.0noble
    Linuxlinuxlinux_kernel7.1
    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 18 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/29d8cc44bbdf7b83a1929912214afe6643c1b4f1
      Referenceadded
      —
      https://git.kernel.org/stable/c/9d017671dcfcec23321fb7962dea624f9e71ddb1
      Referenceadded
      —
      https://git.kernel.org/stable/c/bf8c0b5dd203be94c2ad50e264cec19267c6bd39
      Referenceadded
      —
      https://git.kernel.org/stable/c/c3009418f9fa1dcb3eb86f4d8c92583537b5faa3
      Referenceadded
      —
      https://git.kernel.org/stable/c/f92c90a2a3e6ff6f9f7fe88fde9004b4ca8f956d
      Referenceadded
      —
      https://git.kernel.org/stable/c/fbfde85308b99938a6092c48753214d190ece48d
      Referenceremoved
      https://git.kernel.org/stable/c/29d8cc44bbdf7b83a1929912214afe6643c1b4f1
      —
      Referenceremoved
      https://git.kernel.org/stable/c/9d017671dcfcec23321fb7962dea624f9e71ddb1
      —
      Referenceremoved
      https://git.kernel.org/stable/c/bf8c0b5dd203be94c2ad50e264cec19267c6bd39
      —
      Referenceremoved
      https://git.kernel.org/stable/c/c3009418f9fa1dcb3eb86f4d8c92583537b5faa3
      —
      Referenceremoved
      https://git.kernel.org/stable/c/f92c90a2a3e6ff6f9f7fe88fde9004b4ca8f956d
      —
      Referenceremoved
      https://git.kernel.org/stable/c/fbfde85308b99938a6092c48753214d190ece48d
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/29d8cc44bbdf7b83a1929912214afe6643c1b4f1 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/9d017671dcfcec23321fb7962dea624f9e71ddb1 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/bf8c0b5dd203be94c2ad50e264cec19267c6bd39 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/c3009418f9fa1dcb3eb86f4d8c92583537b5faa3 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/f92c90a2a3e6ff6f9f7fe88fde9004b4ca8f956d Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/fbfde85308b99938a6092c48753214d190ece48d Types: Patch
      —

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

    2. 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/2026/53xxx/CVE-2026-53349.json">CVE-2026-53349</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-784472.html

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

    3. Initial analysis by NVDNVD

      Newly listed as affected:
      • Linux Kernel (6.2 – before 6.6.143; 6.13 – before 6.18.36; 6.7 – before 6.12.94; 6.19 – before 7.0.13; 2.6.20 – before 6.1.176; 7 individual versions)

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

      Show 9 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
      Weakness type (CWE)added
      —
      NVD-CWE-noinfo
      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:*:*:*:*:*:*:*:* versions from (including) 6.2 up to (excluding) 6.6.143 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.13 up to (excluding) 6.18.36 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.7 up to (excluding) 6.12.94 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.19 up to (excluding) 7.0.13 *cpe:2.3:o:linux:linux_kernel:7.1:rc5:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:7.1:rc6:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:7.1:rc7:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 2.6.20 up to (excluding) 6.1.176
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/29d8cc44bbdf7b83a1929912214afe6643c1b4f1 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/9d017671dcfcec23321fb7962dea624f9e71ddb1 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/bf8c0b5dd203be94c2ad50e264cec19267c6bd39 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/c3009418f9fa1dcb3eb86f4d8c92583537b5faa3 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/f92c90a2a3e6ff6f9f7fe88fde9004b4ca8f956d Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/fbfde85308b99938a6092c48753214d190ece48d Types: Patch

      Source identifier: nvd@nist.gov

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