HighCVE-2026-52946

    Linux Kernel: Deadlock (CVE-2026-52946)

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

    What is affected, what to do

    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 2.6.12..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
    • Linux Kernel lt 7.1..7.1.1
    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 7.1.1
    • Linux Kernel 7.2

    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, SUSE, Debian LTS, BSI, CVE.org, Msrc Update Guide

    0.5 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 40.5

    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
    69.91 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
    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
    0.5 %
    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
    40.5
    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: none known · automatable · Technical impact: partial
    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

    In the Linux kernel, the following vulnerability has been resolved:

    fs/fcntl: fix SOFTIRQ-unsafe lock order in fasync signaling

    A SOFTIRQ-safe to SOFTIRQ-unsafe lock order deadlock can occur in send_sigio() and send_sigurg() when a process group receives a signal.

    When FASYNC is configured for a process group (PIDTYPE_PGID), both functions use read_lock(&tasklist_lock) to traverse the task list. However, they are frequently called from softirq context:

    • send_sigio() via input_inject_event -> kill_fasync
    • send_sigurg() via tcp_check_urg -> sk_send_sigurg (NET_RX_SOFTIRQ)

    The deadlock is caused by the rwlock writer fairness mechanism:

    1. CPU 0 (process context) holds read_lock(&tasklist_lock) in do_wait().
    2. CPU 1 (process context) attempts write_lock(&tasklist_lock) in fork() or exit() and spins, which blocks all new readers.
    3. CPU 0 is interrupted by a softirq (e.g., TCP URG packet reception).
    4. The softirq calls send_sigurg() and attempts to acquire read_lock(&tasklist_lock), deadlocking because CPU 1 is waiting.

    Since PID hashing and do_each_pid_task() traversals are already RCU-protected, the read_lock on tasklist_lock is no longer strictly required for safe traversal. Fix this by replacing tasklist_lock with rcu_read_lock(), aligning the process group signaling path with the single-PID path. This also mitigates a potential remote denial of service vector via TCP URG packets.

    Lockdep splat:

    WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected [...] Chain exists of: &dev->event_lock --> &f_owner->lock --> tasklist_lock

    Possible interrupt unsafe locking scenario: CPU0 CPU1 ---- ---- lock(tasklist_lock); local_irq_disable(); lock(&dev->event_lock); lock(&f_owner->lock); lock(&dev->event_lock);

    *** DEADLOCK ***

    Source: siemens_advisory, suse_csaf, Debian LTS Advisories, BSI WID Portal, BSI CSAF, NVD (NIST), CVE.org (MITRE), cvelistv5, 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
    • 7.1 – < 7.1.1
    • 2.6.12 – < 5.10.259
    • 6.7 – < 6.12.94
    • 6.13 – < 6.18.36
    • 5.11 – < 5.15.210
    • 5.16 – < 6.1.176
    • —
    • 6.19 – < 7.0.13
    • 6.2 – < 6.6.143
    • 7.1.1
    • 5.10.259
    • 6.12.94
    • 6.18.36
    • 5.15.210
    • 6.1.176
    • 7.2
    • 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_kernel2.6.12
    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

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Weakness type (CWE)added
      —
      CWE-362

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

    2. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: yes

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-52946","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-16T15:23:11.779977Z"}

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

    3. Record modifiedSiemens ADP

      Show 3 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/2026/52xxx/CVE-2026-52946.json">CVE-2026-52946</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-457936.html
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-784472.html

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

    4. Record modifiedLinux

      Show 27 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/00633c4683828acd5256fa8d5163f440d74bbe71
      Referenceadded
      —
      https://git.kernel.org/stable/c/1bee417678f1135e35b25a37734db46aa94258d2
      Referenceadded
      —
      https://git.kernel.org/stable/c/20a93e397abe850c49b6fa0e8cc827b5f634a8f5
      Referenceadded
      —
      https://git.kernel.org/stable/c/32dbd5ce4be3a3ed7e00f8af18795cc84fc50a33
      Referenceadded
      —
      https://git.kernel.org/stable/c/36c1b57b2ecf3c61ac93f5f07bd29b6f21e226ed
      Referenceadded
      —
      https://git.kernel.org/stable/c/54626335ea4174ab2d9a183b511d825f6765e47b
      Referenceadded
      —
      https://git.kernel.org/stable/c/897d6a7247739fb1528f98c575df4f2e5de7f994
      Referenceadded
      —
      https://git.kernel.org/stable/c/b5fa9e32fb6718f70c986ee14dd5d01b4846f331
      Referenceadded
      —
      https://git.kernel.org/stable/c/bfcc8e8d8a495bb34cae9e620adfb75fb13a3954
      Referenceremoved
      https://git.kernel.org/stable/c/00633c4683828acd5256fa8d5163f440d74bbe71
      —
      Referenceremoved
      https://git.kernel.org/stable/c/1bee417678f1135e35b25a37734db46aa94258d2
      —
      Referenceremoved
      https://git.kernel.org/stable/c/20a93e397abe850c49b6fa0e8cc827b5f634a8f5
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      Referenceremoved
      https://git.kernel.org/stable/c/32dbd5ce4be3a3ed7e00f8af18795cc84fc50a33
      —
      Referenceremoved
      https://git.kernel.org/stable/c/36c1b57b2ecf3c61ac93f5f07bd29b6f21e226ed
      —
      Referenceremoved
      https://git.kernel.org/stable/c/54626335ea4174ab2d9a183b511d825f6765e47b
      —
      Referenceremoved
      https://git.kernel.org/stable/c/897d6a7247739fb1528f98c575df4f2e5de7f994
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      Referenceremoved
      https://git.kernel.org/stable/c/b5fa9e32fb6718f70c986ee14dd5d01b4846f331
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      Referenceremoved
      https://git.kernel.org/stable/c/bfcc8e8d8a495bb34cae9e620adfb75fb13a3954
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/00633c4683828acd5256fa8d5163f440d74bbe71 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/1bee417678f1135e35b25a37734db46aa94258d2 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/20a93e397abe850c49b6fa0e8cc827b5f634a8f5 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/32dbd5ce4be3a3ed7e00f8af18795cc84fc50a33 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/36c1b57b2ecf3c61ac93f5f07bd29b6f21e226ed Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/54626335ea4174ab2d9a183b511d825f6765e47b Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/897d6a7247739fb1528f98c575df4f2e5de7f994 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/b5fa9e32fb6718f70c986ee14dd5d01b4846f331 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/bfcc8e8d8a495bb34cae9e620adfb75fb13a3954 Types: Patch
      —

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

    5. 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-2026-52946.json">CVE-2026-52946</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-019113.html

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

    Show 3 older changes

    1. Record modifiedLinux

      1 individual change: Affected versions (publisher)

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)changed
      Linux, Linux
      Linux, Linux

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

    2. Record modifiedLinux

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/00633c4683828acd5256fa8d5163f440d74bbe71
      Affected versions (publisher)changed
      Linux, Linux
      Linux, Linux

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

    3. ReceivedLinux

      Description added or changed

      Show 10 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Linux, Linux
      Descriptionadded
      —
      In the Linux kernel, the following vulnerability has been resolved: fs/fcntl: fix SOFTIRQ-unsafe lock order in fasync signaling A SOFTIRQ-safe to SOFTIRQ-unsafe lock order deadlock can occur in send_sigio() and send_sigurg() when a process group receives a signal. When FASYNC is configured for a process group (PIDTYPE_PGID), both functions use read_lock(&tasklist_lock) to traverse the task list. However, they are frequently called from softirq context: - send_sigio() via input_inject_event -> kill_fasync - send_sigurg() via tcp_check_urg -> sk_send_sigurg (NET_RX_SOFTIRQ) The deadlock is caused by the rwlock writer fairness mechanism: 1. CPU 0 (process context) holds read_lock(&tasklist_lock) in do_wait(). 2. CPU 1 (process context) attempts write_lock(&tasklist_lock) in fork() or exit() and spins, which blocks all new readers. 3. CPU 0 is interrupted by a softirq (e.g., TCP URG packet reception). 4. The softirq calls send_sigurg() and attempts to acquire read_lock(&tasklist_lock), deadlocking because CPU 1 is waiting. Since PID hashing and do_each_pid_task() traversals are already RCU-protected, the read_lock on tasklist_lock is no longer strictly required for safe traversal. Fix this by replacing tasklist_lock with rcu_read_lock(), aligning the process group signaling path with the single-PID path. This also mitigates a potential remote denial of service vector via TCP URG packets. Lockdep splat: ===================================================== WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected [...] Chain exists of: &dev->event_lock --> &f_owner->lock --> tasklist_lock Possible interrupt unsafe locking scenario: CPU0 CPU1 ---- ---- lock(tasklist_lock); local_irq_disable(); lock(&dev->event_lock); lock(&f_owner->lock); <Interrupt> lock(&dev->event_lock); *** DEADLOCK ***
      Referenceadded
      —
      https://git.kernel.org/stable/c/1bee417678f1135e35b25a37734db46aa94258d2
      Referenceadded
      —
      https://git.kernel.org/stable/c/20a93e397abe850c49b6fa0e8cc827b5f634a8f5
      Referenceadded
      —
      https://git.kernel.org/stable/c/32dbd5ce4be3a3ed7e00f8af18795cc84fc50a33
      Referenceadded
      —
      https://git.kernel.org/stable/c/36c1b57b2ecf3c61ac93f5f07bd29b6f21e226ed
      Referenceadded
      —
      https://git.kernel.org/stable/c/54626335ea4174ab2d9a183b511d825f6765e47b
      Referenceadded
      —
      https://git.kernel.org/stable/c/897d6a7247739fb1528f98c575df4f2e5de7f994
      Referenceadded
      —
      https://git.kernel.org/stable/c/b5fa9e32fb6718f70c986ee14dd5d01b4846f331
      Referenceadded
      —
      https://git.kernel.org/stable/c/bfcc8e8d8a495bb34cae9e620adfb75fb13a3954

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

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