MediumCVE-2026-99233

    Linux Kernel: security vulnerability (CVE-2026-99233)

    Published Last modified Sources: BSI, Msrc Update Guide, CVE.org

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    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: tracing/histograms: Verify event_call identity when updating synth_event refcount In event_hist_trigger_parse() and hist_unreg_all(), the histogram registration and unregistration paths look up find_synth_event() using trace_event_name(file->event_call) and adjust se->ref if a match is found. Because find_synth_event() only compares the event basename, registering or removing a histogram on a non-synthetic trace event whose basename matches a synthetic event erroneously modifies the synthetic event's reference count.

    Update Linux Kernel to version 6.1.191, Linux Kernel to version 6.6.161, Linux Kernel to version 6.12.115.

    Affected
    • Linux Kernel lt 4.17..6.1.191
    • Linux Kernel lt 6.2..6.6.161
    • Linux Kernel lt 6.7..6.12.115
    • Linux Kernel lt 6.13..6.18.60
    • Linux Kernel lt 6.19..7.2.14
    • Linux Kernel lt 7.3..7.3.1
    • Linux Kernel lt 7.4..7.4-rc1
    Fixed in
    • Linux Kernel 6.1.191
    • Linux Kernel 6.6.161
    • Linux Kernel 6.12.115
    • Linux Kernel 6.18.60
    • Linux Kernel 7.2.14
    • Linux Kernel 7.3.1
    • Linux Kernel 7.4-rc1

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

    Metrics

    4.4

    Priority

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

    Source: Vendor (CNA), CVSS v3

    4.4

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: BSI, Msrc Update Guide, CVE.org

    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
    52.03 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
    4.4 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
    4.4
    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: tracing/histograms: Verify event_call identity when updating synth_event refcount In event_hist_trigger_parse() and hist_unreg_all(), the histogram registration and unregistration paths look up find_synth_event() using trace_event_name(file->event_call) and adjust se->ref if a match is found. Because find_synth_event() only compares the event basename, registering or removing a histogram on a non-synthetic trace event whose basename matches a synthetic event erroneously modifies the synthetic event's reference count. If a histogram is registered on the non-synthetic event before the synthetic event is created and removed afterwards, se->ref is decremented without a matching increment, allowing the synthetic event to be freed while an active histogram action still holds a pointer to it. Introduce find_synth_event_call() to verify that &se->call matches file->event_call before adjusting se->ref.

    Source: BSI WID Portal, BSI CSAF, Microsoft Security Update Guide, cvelistv5, NVD (NIST)

    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
    • 4.17 – < 6.1.191
    • 7.3 – < 7.3.1
    • 6.7 – < 6.12.115
    • 6.13 – < 6.18.60
    • 6.2 – < 6.6.161
    • 6.19 – < 7.2.14
    • 7.4 – < 7.4-rc1
    • 6.1.191
    • 7.3.1
    • 6.12.115
    • 6.18.60
    • 6.6.161
    • 7.2.14
    • 7.4-rc1

    Vendors and products

    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 2 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/2026/99xxx/CVE-2026-99233.json">CVE-2026-99233</a>
      Referenceadded
      —
      https://git.kernel.org/stable/c/3403d9bb27ebc3572bd048620746b4414e073bf9

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

    2. ReceivedLinux

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

      Description added or changed

      Show 9 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      In the Linux kernel, the following vulnerability has been resolved: tracing/histograms: Verify event_call identity when updating synth_event refcount In event_hist_trigger_parse() and hist_unreg_all(), the histogram registration and unregistration paths look up find_synth_event() using trace_event_name(file->event_call) and adjust se->ref if a match is found. Because find_synth_event() only compares the event basename, registering or removing a histogram on a non-synthetic trace event whose basename matches a synthetic event erroneously modifies the synthetic event's reference count. If a histogram is registered on the non-synthetic event before the synthetic event is created and removed afterwards, se->ref is decremented without a matching increment, allowing the synthetic event to be freed while an active histogram action still holds a pointer to it. Introduce find_synth_event_call() to verify that &se->call matches file->event_call before adjusting se->ref.
      CVSSadded
      —
      AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/99xxx/CVE-2026-99233.json">CVE-2026-99233</a>
      Referenceadded
      —
      https://git.kernel.org/stable/c/06e816bed499fe47f39f12044382cc5d064485fb
      Referenceadded
      —
      https://git.kernel.org/stable/c/23b4106e8b35823acc79e206c7745f55b9cfd78b
      Referenceadded
      —
      https://git.kernel.org/stable/c/381f543ed35c434d5b707369aa5dcd69ecf440af
      Referenceadded
      —
      https://git.kernel.org/stable/c/4472579bd1c83708b6fe623c870cdf728e947205
      Referenceadded
      —
      https://git.kernel.org/stable/c/5597bb8db6855fcb97a67196d227fea359bcd81c
      Referenceadded
      —
      https://git.kernel.org/stable/c/cf4e31d5da80fae4c9cdbe7af55b7c3ad213f0e4

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

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