CriticalCVE-2026-52947

    Linux Kernel: Use-After-Free (CVE-2026-52947)

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

    What is affected, what to do

    A flaw was found in the Linux kernel's `qrtr` network subsystem. A race condition exists in the `qrtr_port_remove()` function where the socket reference count is decremented prematurely.

    Update Linux Kernel to version 5.10.259, Linux Kernel to version 5.15.210, Linux Kernel to version 6.1.176.

    Affected
    • Linux Kernel lt 4.7..5.10.259
    • Linux Kernel lt 5.11..5.15.210
    • Linux Kernel lt 5.16..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 5.10.259
    • Linux Kernel 5.15.210
    • 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

    9.8

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

    0.1 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 1.1

    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
    58.39 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
    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
    0.1 %
    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
    1.1
    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
    CISA assessment (SSVC)
    Exploitation: none known · not 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-362

    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

    A flaw was found in the Linux kernel's `qrtr` network subsystem. A race condition exists in the `qrtr_port_remove()` function where the socket reference count is decremented prematurely. This allows a concurrent reader to access a socket whose reference count has dropped to zero, potentially leading to a Use-After-Free (UAF) vulnerability. An attacker could exploit this to cause memory corruption, leading to system instability or a denial of service.

    Source: suse_csaf, Debian LTS Advisories, Ubuntu Security Notices, BSI WID Portal, BSI CSAF, siemens_advisory, redhat_csaf, Microsoft Security Update Guide, cvelistv5, NVD (NIST), CVE.org (MITRE)

    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
    • 6.7 – < 6.12.94
    • 6.13 – < 6.18.36
    • 5.11 – < 5.15.210
    • —
    • 4.7 – < 5.10.259
    • 5.16 – < 6.1.176
    • 6.19 – < 7.0.13
    • 6.2 – < 6.6.143
    • 6.12.94
    • 6.18.36
    • 5.15.210
    • 7.1
    • 5.10.259
    • 6.1.176
    • 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
    Linuxdebianlinuxbullseye
    Linuxdebianlinux-6.1bullseye
    Linuxlinuxlinux_kernel7.1
    Linuxlinuxlinux_kernel—

    Weakness classes (CWE)

    • CWE-362Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

      Class

      The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

      Entry at MITRE CWE-362

    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-362

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      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Weakness type (CWE)added
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      CWE-362

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

    2. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-52947","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:23:14.590748Z"}

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

    3. Record modifiedLinux

      Show 24 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
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      https://git.kernel.org/stable/c/03bfa95e452e2b6ccd76a332060ae4feaf5ad84d
      Referenceadded
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      https://git.kernel.org/stable/c/2047c2aa0963bb2872fd722300a15bcb441a4c00
      Referenceadded
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      https://git.kernel.org/stable/c/2aa4c12723fe432e623462a3be42a197a128722b
      Referenceadded
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      https://git.kernel.org/stable/c/3b20ec8f31e8a6a6782243f473b0abd3463621df
      Referenceadded
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      https://git.kernel.org/stable/c/474293d90880622fde9d2430fb0165767090f7b3
      Referenceadded
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      https://git.kernel.org/stable/c/7de2d447072be3b1a76793f034432338fc9c494b
      Referenceadded
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      https://git.kernel.org/stable/c/a2171131ecda1ed61a594a1eb715e75fdad0fef5
      Referenceadded
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      https://git.kernel.org/stable/c/ab269990ed58143a92a263be1bee626d82ac03da
      Referenceremoved
      https://git.kernel.org/stable/c/03bfa95e452e2b6ccd76a332060ae4feaf5ad84d
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      Referenceremoved
      https://git.kernel.org/stable/c/2047c2aa0963bb2872fd722300a15bcb441a4c00
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      https://git.kernel.org/stable/c/2aa4c12723fe432e623462a3be42a197a128722b
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      Referenceremoved
      https://git.kernel.org/stable/c/3b20ec8f31e8a6a6782243f473b0abd3463621df
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      Referenceremoved
      https://git.kernel.org/stable/c/474293d90880622fde9d2430fb0165767090f7b3
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      Referenceremoved
      https://git.kernel.org/stable/c/7de2d447072be3b1a76793f034432338fc9c494b
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      Referenceremoved
      https://git.kernel.org/stable/c/a2171131ecda1ed61a594a1eb715e75fdad0fef5
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      Referenceremoved
      https://git.kernel.org/stable/c/ab269990ed58143a92a263be1bee626d82ac03da
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      Reference typeremoved
      https://git.kernel.org/stable/c/03bfa95e452e2b6ccd76a332060ae4feaf5ad84d Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/2047c2aa0963bb2872fd722300a15bcb441a4c00 Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/2aa4c12723fe432e623462a3be42a197a128722b Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/3b20ec8f31e8a6a6782243f473b0abd3463621df Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/474293d90880622fde9d2430fb0165767090f7b3 Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/7de2d447072be3b1a76793f034432338fc9c494b Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/a2171131ecda1ed61a594a1eb715e75fdad0fef5 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/ab269990ed58143a92a263be1bee626d82ac03da 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/2026/52xxx/CVE-2026-52947.json">CVE-2026-52947</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-784472.html

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

    5. ReceivedLinux

      Description added or changed

      Show 10 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
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      Linux, Linux
      Descriptionadded
      —
      In the Linux kernel, the following vulnerability has been resolved: net: qrtr: fix refcount saturation and potential UAF in qrtr_port_remove In qrtr_port_remove(), the socket reference count is decremented via __sock_put() before the port is removed from the qrtr_ports XArray and before the RCU grace period elapses. This breaks the fundamental RCU update paradigm. It exposes a race window where a concurrent RCU reader (such as qrtr_reset_ports() or qrtr_port_lookup()) can obtain a pointer to the socket from the XArray, and attempt to call sock_hold() on a socket whose reference count has already dropped to zero. This exact race condition was hit during syzkaller fuzzing, leading to the following refcount saturation warning and a potential Use-After-Free: refcount_t: saturated; leaking memory. WARNING: CPU: 3 PID: 1273 at lib/refcount.c:22 refcount_warn_saturate+0xae/0x1d0 Modules linked in: qrtr(+) bochs drm_shmem_helper ... Call Trace: <TASK> qrtr_reset_ports net/qrtr/af_qrtr.c:768 [inline] [qrtr] __qrtr_bind.isra.0+0x48b/0x570 net/qrtr/af_qrtr.c:805 [qrtr] qrtr_bind+0x17d/0x210 net/qrtr/af_qrtr.c:901 [qrtr] kernel_bind+0xe4/0x120 net/socket.c:3592 qrtr_ns_init+0x1a6/0x380 net/qrtr/ns.c:715 [qrtr] qrtr_proto_init+0x3b/0xff0 net/qrtr/af_qrtr.c:169 [qrtr] do_one_initcall+0xf5/0x5e0 init/main.c:1283 ... </TASK> Fix this by deferring the reference count decrement until after the xa_erase() and the synchronize_rcu() complete. (Note: The v1 of this patch incorrectly replaced __sock_put() with sock_put(). As Simon Horman pointed out, the callers of qrtr_port_remove() still hold a reference to the socket, so freeing the socket memory here would lead to a subsequent UAF in the caller. Thus, the __sock_put() is kept, but only repositioned to close the RCU race.)
      Referenceadded
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      https://git.kernel.org/stable/c/03bfa95e452e2b6ccd76a332060ae4feaf5ad84d
      Referenceadded
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      https://git.kernel.org/stable/c/2047c2aa0963bb2872fd722300a15bcb441a4c00
      Referenceadded
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      https://git.kernel.org/stable/c/2aa4c12723fe432e623462a3be42a197a128722b
      Referenceadded
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      https://git.kernel.org/stable/c/3b20ec8f31e8a6a6782243f473b0abd3463621df
      Referenceadded
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      https://git.kernel.org/stable/c/474293d90880622fde9d2430fb0165767090f7b3
      Referenceadded
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      https://git.kernel.org/stable/c/7de2d447072be3b1a76793f034432338fc9c494b
      Referenceadded
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      https://git.kernel.org/stable/c/a2171131ecda1ed61a594a1eb715e75fdad0fef5
      Referenceadded
      —
      https://git.kernel.org/stable/c/ab269990ed58143a92a263be1bee626d82ac03da

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

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