MediumCVE-2026-23157

    Linux Kernel: Deadlock (CVE-2026-23157)

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

    What is affected, what to do

    Update Linux Kernel to version 5.15.209, Linux Kernel to version 6.1.167, Linux Kernel to version 6.6.130.

    Affected
    • Linux Kernel lt 2.6.29..5.15.209
    • Linux Kernel lt 5.16..6.1.167
    • Linux Kernel lt 6.2..6.6.130
    • Linux Kernel lt 6.7..6.12.78
    • Linux Kernel lt 6.13..6.18.9
    Fixed in
    • Linux Kernel 5.15.209
    • Linux Kernel 6.1.167
    • Linux Kernel 6.6.130
    • Linux Kernel 6.12.78
    • Linux Kernel 6.18.9
    • Linux Kernel 6.19

    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, Debian, SUSE, Siemens ProductCERT, Ubuntu, BSI, CVE.org, Msrc Update Guide, EUVD

    0.1 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 3.2

    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
    41.83 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
    3.2
    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:

    btrfs: do not strictly require dirty metadata threshold for metadata writepages

    [BUG] There is an internal report that over 1000 processes are waiting at the io_schedule_timeout() of balance_dirty_pages(), causing a system hang and trigger a kernel coredump.

    The kernel is v6.4 kernel based, but the root problem still applies to any upstream kernel before v6.18.

    [CAUSE] From Jan Kara for his wisdom on the dirty page balance behavior first.

    This cgroup dirty limit was what was actually playing the role here because the cgroup had only a small amount of memory and so the dirty limit for it was something like 16MB.

    Dirty throttling is responsible for enforcing that nobody can dirty (significantly) more dirty memory than there's dirty limit. Thus when a task is dirtying pages it periodically enters into balance_dirty_pages() and we let it sleep there to slow down the dirtying.

    When the system is over dirty limit already (either globally or within a cgroup of the running task), we will not let the task exit from balance_dirty_pages() until the number of dirty pages drops below the limit.

    So in this particular case, as I already mentioned, there was a cgroup with relatively small amount of memory and as a result with dirty limit set at 16MB. A task from that cgroup has dirtied about 28MB worth of pages in btrfs btree inode and these were practically the only dirty pages in that cgroup.

    So that means the only way to reduce the dirty pages of that cgroup is to writeback the dirty pages of btrfs btree inode, and only after that those processes can exit balance_dirty_pages().

    Now back to the btrfs part, btree_writepages() is responsible for writing back dirty btree inode pages.

    The problem here is, there is a btrfs internal threshold that if the btree inode's dirty bytes are below the 32M threshold, it will not do any writeback.

    This behavior is to batch as much metadata as possible so we won't write back those tree blocks and then later re-COW them again for another modification.

    This internal 32MiB is higher than the existing dirty page size (28MiB), meaning no writeback will happen, causing a deadlock between btrfs and cgroup:

    • Btrfs doesn't want to write back btree inode until more dirty pages

    • Cgroup/MM doesn't want more dirty pages for btrfs btree inode Thus any process touching that btree inode is put into sleep until the number of dirty pages is reduced.

    Thanks Jan Kara a lot for the analysis of the root cause.

    [ENHANCEMENT] Since kernel commit b55102826d7d ("btrfs: set AS_KERNEL_FILE on the btree_inode"), btrfs btree inode pages will only be charged to the root cgroup which should have a much larger limit than btrfs' 32MiB threshold. So it should not affect newer kernels.

    But for all current LTS kernels, they are all affected by this problem, and backporting the whole AS_KERNEL_FILE may not be a good idea.

    Even for newer kernels I still think it's a good idea to get rid of the internal threshold at btree_writepages(), since for most cases cgroup/MM has a better view of full system memory usage than btrfs' fixed threshold.

    For internal callers using btrfs_btree_balance_dirty() since that function is already doing internal threshold check, we don't need to bother them.

    But for external callers of btree_writepages(), just respect their requests and write back whatever they want, ignoring the internal btrfs threshold to avoid such deadlock on btree inode dirty page balancing.

    Source: Debian LTS Advisories, Debian Security Advisories, suse_csaf, siemens_advisory, Ubuntu Security Notices, BSI WID Portal, BSI CSAF, NVD (NIST), CVE.org (MITRE), cvelistv5, Microsoft Security Update Guide, 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
    • —
    • 6.2 – < 6.6.130
    • 6.7 – < 6.12.78
    • 2.6.29 – < 5.15.209
    • 6.13 – < 6.18.9
    • 5.16 – < 6.1.167
    • 6.19
    • 6.6.130
    • 6.12.78
    • 5.15.209
    • 6.18.9
    • 6.1.167
    IBMQRadar SIEM
    • <7.5.0 UP15 IF02
    • —
    SiemensSIMATIC S7
    • 1500 TM MFP V1.1.1 GNU/Linux subsystem
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbookworm
    Linuxdebianlinuxtrixie
    Linuxdebianlinux-6.1bullseye
    Linuxlinuxlinux_kernel6.19
    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 14 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
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      https://git.kernel.org/stable/c/0c3666ec188640c20e254011e7adf4464c32ee58
      Referenceadded
      —
      https://git.kernel.org/stable/c/4357e02cafabe01c2d737ceb4c4c6382fc2ee10a
      Referenceadded
      —
      https://git.kernel.org/stable/c/4e159150a9a56d66d247f4b5510bed46fe58aa1c
      Referenceadded
      —
      https://git.kernel.org/stable/c/629666d20c7dcd740e193ec0631fdff035b1f7d6
      Referenceadded
      —
      https://git.kernel.org/stable/c/6a8b6242eaa1dd7a0de2d6de6420d10ffe68db90
      Referenceadded
      —
      https://git.kernel.org/stable/c/bb9be3f713652e330df00f3724c18c7a5469e7ac
      Referenceremoved
      https://git.kernel.org/stable/c/0c3666ec188640c20e254011e7adf4464c32ee58
      —
      Referenceremoved
      https://git.kernel.org/stable/c/4357e02cafabe01c2d737ceb4c4c6382fc2ee10a
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      Referenceremoved
      https://git.kernel.org/stable/c/4e159150a9a56d66d247f4b5510bed46fe58aa1c
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      Referenceremoved
      https://git.kernel.org/stable/c/629666d20c7dcd740e193ec0631fdff035b1f7d6
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      Referenceremoved
      https://git.kernel.org/stable/c/6a8b6242eaa1dd7a0de2d6de6420d10ffe68db90
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      Referenceremoved
      https://git.kernel.org/stable/c/bb9be3f713652e330df00f3724c18c7a5469e7ac
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      Reference typeremoved
      https://git.kernel.org/stable/c/4e159150a9a56d66d247f4b5510bed46fe58aa1c Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/629666d20c7dcd740e193ec0631fdff035b1f7d6 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/2026/23xxx/CVE-2026-23157.json">CVE-2026-23157</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-784472.html

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

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