HighCVE-2026-63913

    Linux Kernel: Improper Input Validation (CVE-2026-63913)

    Published Last modified Sources: Ubuntu, SUSE, Red Hat, CVE.org, BSI

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    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check An unintended behavior in the TCP conntrack state machine allows a connection to be forced into the CLOSE state using an RST packet with an invalid sequence number. Specifically, after a SYN packet is observed, an RST with an invalid SEQ can transition the conntrack entry to TCP_CONNTRACK_CLOSE, regardless of whether the RST corresponds to the expected reply direction.

    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 2.6.15..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..6.12.93
    • Linux Kernel lt 6.13..6.18.35
    • Linux Kernel lt 6.19..7.0.12
    Fixed in
    • Linux Kernel 5.10.259
    • Linux Kernel 5.15.210
    • Linux Kernel 6.1.176
    • Linux Kernel 6.6.143
    • Linux Kernel 6.12.93
    • Linux Kernel 6.18.35
    • Linux Kernel 7.0.12
    • Linux Kernel 7.1

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

    Metrics

    8.2

    Priority

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

    Source: NVD, CVSS v3

    8.2

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Ubuntu, SUSE, Red Hat, CVE.org, BSI

    1.0 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 62.0

    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
    92.45 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
    8.2 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
    8.2
    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
    1.0 %
    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
    62.0
    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-20

    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: netfilter: conntrack: tcp: do not force CLOSE on invalid-seq RST without direction check An unintended behavior in the TCP conntrack state machine allows a connection to be forced into the CLOSE state using an RST packet with an invalid sequence number. Specifically, after a SYN packet is observed, an RST with an invalid SEQ can transition the conntrack entry to TCP_CONNTRACK_CLOSE, regardless of whether the RST corresponds to the expected reply direction. The relevant code path assumes the RST is a response to an outgoing SYN, but does not validate packet direction or ensure that a matching SYN was actually sent in the opposite direction. As a result, a crafted packet sequence consisting of a SYN followed by an invalid-sequence RST can prematurely terminate an active NAT entry. This makes connection teardown easier than intended. So, tighten the state transition logic to ensure that RST-triggered CLOSE transitions only occur when the RST is a valid response to a previously observed SYN in the correct direction.

    Source: Ubuntu Security Notices, suse_csaf, redhat_csaf, NVD (NIST), cvelistv5, BSI WID Portal, BSI CSAF

    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
    • 2.6.15 – < 5.10.259
    • 6.13 – < 6.18.35
    • 6.7 – < 6.12.93
    • 5.11 – < 5.15.210
    • 6.19 – < 7.0.12
    • —
    • 5.16 – < 6.1.176
    • 6.2 – < 6.6.143
    • 5.10.259
    • 6.18.35
    • 6.12.93
    • 5.15.210
    • 7.0.12
    • 7.1
    • 6.1.176
    • 6.6.143
    IBMDataPower Gateway
    • < 11.0.0.3
    • < 10.6.0.11
    • < 10.5.0.23
    • 11.0.0.3
    • 10.6.0.11
    • 10.5.0.23
    IBMQRadar SIEM
    • < 7.6.0.3
    • <7.5.0 UP16 IF01
    • 7.6.0.3
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxubuntulinuxnoble
    Linuxubuntulinux-awsnoble
    Linuxubuntulinux-aws-6.8jammy
    Linuxubuntulinux-aws-fipsnoble
    Linuxubuntulinux-azurenoble
    Linuxubuntulinux-azure-6.8jammy
    Linuxubuntulinux-azure-fdenoble
    Linuxubuntulinux-azure-fde-6.8jammy
    Linuxubuntulinux-azure-fipsnoble
    Linuxubuntulinux-fipsnoble
    Linuxubuntulinux-gcpnoble
    Linuxubuntulinux-gcp-6.8jammy
    Linuxubuntulinux-gcp-fipsnoble
    Linuxubuntulinux-gkenoble
    Linuxubuntulinux-gkeopnoble
    Linuxubuntulinux-ibmnoble
    Linuxubuntulinux-ibm-6.8jammy
    Linuxubuntulinux-lowlatencynoble
    Linuxubuntulinux-lowlatency-hwe-6.8jammy
    Linuxubuntulinux-nvidiajammy
    Linuxubuntulinux-nvidianoble
    Linuxubuntulinux-nvidia-6.8jammy
    Linuxubuntulinux-nvidia-lowlatencynoble
    Linuxubuntulinux-nvidia-tegrajammy

    Weakness classes (CWE)

    • CWE-20Improper Input Validation

      Class

      The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

      Entry at MITRE CWE-20

    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. Initial analysis by NVDNVD

      Newly listed as affected:
      • Linux Kernel (5.16 – before 6.1.176; 6.13 – before 6.18.35; 6.2 – before 6.6.143; 6.7 – before 6.12.93; 5.11 – before 5.15.210; 2.6.15 – before 5.10.259; 6.19 – before 7.0.12; 5 individual versions)
      Show 9 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      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) 5.16 up to (excluding) 6.1.176 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.13 up to (excluding) 6.18.35 *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) 6.7 up to (excluding) 6.12.93 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 5.11 up to (excluding) 5.15.210 *cpe:2.3:o:linux:linux_kernel:7.1:rc5:*:*:*:*:*:* *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 2.6.15 up to (excluding) 5.10.259 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.19 up to (excluding) 7.0.12
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/2006979a15af5404bf932a325357683c0bac1656 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/2bb6d82b586ea5a4cb73bbdd6b7432e96096bc77 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/6476c17d536dbd321c073242e762ddb2713a1238 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/b98ab51c45c5608a1c19ce7fd17a3032469bb83f Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/d67c6adee8d1b65330d0174c4c367faba14e80a8 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/f206def4e86d810f927ba1d8e322ea72b29bce58 Types: Patch
      Reference typeadded
      —
      kernel.org: https://git.kernel.org/stable/c/f5547bebc416d56f56fb5b86dc20aabfa42165a0 Types: Patch

      Source identifier: nvd@nist.gov

    2. Record modifiedCISA ADP

      Weakness type: CWE-20

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Weakness type (CWE)added
      —
      CWE-20

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

    3. Record modifiedLinux

      Show 16 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/2006979a15af5404bf932a325357683c0bac1656
      Referenceadded
      —
      https://git.kernel.org/stable/c/2bb6d82b586ea5a4cb73bbdd6b7432e96096bc77
      Referenceadded
      —
      https://git.kernel.org/stable/c/6476c17d536dbd321c073242e762ddb2713a1238
      Referenceadded
      —
      https://git.kernel.org/stable/c/b98ab51c45c5608a1c19ce7fd17a3032469bb83f
      Referenceadded
      —
      https://git.kernel.org/stable/c/bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a
      Referenceadded
      —
      https://git.kernel.org/stable/c/d67c6adee8d1b65330d0174c4c367faba14e80a8
      Referenceadded
      —
      https://git.kernel.org/stable/c/f206def4e86d810f927ba1d8e322ea72b29bce58
      Referenceadded
      —
      https://git.kernel.org/stable/c/f5547bebc416d56f56fb5b86dc20aabfa42165a0
      Referenceremoved
      https://git.kernel.org/stable/c/2006979a15af5404bf932a325357683c0bac1656
      —
      Referenceremoved
      https://git.kernel.org/stable/c/2bb6d82b586ea5a4cb73bbdd6b7432e96096bc77
      —
      Referenceremoved
      https://git.kernel.org/stable/c/6476c17d536dbd321c073242e762ddb2713a1238
      —
      Referenceremoved
      https://git.kernel.org/stable/c/b98ab51c45c5608a1c19ce7fd17a3032469bb83f
      —
      Referenceremoved
      https://git.kernel.org/stable/c/bed6e04be8e6b9133d8b16d5a42d0e0ce674fa9a
      —
      Referenceremoved
      https://git.kernel.org/stable/c/d67c6adee8d1b65330d0174c4c367faba14e80a8
      —
      Referenceremoved
      https://git.kernel.org/stable/c/f206def4e86d810f927ba1d8e322ea72b29bce58
      —
      Referenceremoved
      https://git.kernel.org/stable/c/f5547bebc416d56f56fb5b86dc20aabfa42165a0
      —

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

    4. 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-2026-63913","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-16T15:33:11.442709Z"}

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

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