HighCVE-2026-23397

    Linux Kernel: Out-of-Bounds Read (CVE-2026-23397)

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

    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: nfnetlink_osf: validate individual option lengths in fingerprints nfnl_osf_add_callback() validates opt_num bounds and string NUL-termination but does not check individual option length fields. A zero-length option causes nf_osf_match_one() to enter the option matching loop even when foptsize sums to zero, which matches packets with no TCP options where ctx->optp is NULL: Oops: general protection fault KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: 0010:nf_osf_match_one (net/netfilter/nfnetlink_osf.c:98) Call Trace: nf_osf_match (net/netfilter/nfnetlink_osf.c:227) xt_osf_match_packet (net/netfilter/xt_osf.c:32) ipt_do_table (net/ipv4/netfilter/ip_tables.c:293) nf_hook_slow (net/netfilter/core.c:623) ip_local_deliver (net/ipv4/ip_input.c:262) ip_rcv (net/ipv4/ip_input.c:573) Additionally, an MSS option (kind=2) with length < 4 causes out-of-bounds reads when nf_osf_match_one() unconditionally accesses optp[2] and optp[3] for MSS value extraction.

    Update Linux Kernel to version 5.10.253, Linux Kernel to version 5.15.203, Linux Kernel to version 6.1.167.

    Affected
    • Linux Kernel lt 2.6.31..5.10.253
    • Linux Kernel lt 5.11..5.15.203
    • 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..6.18.20
    • Linux Kernel lt 6.19..6.19.10
    • Linux Kernel lt 6.20..7.0
    Fixed in
    • Linux Kernel 5.10.253
    • Linux Kernel 5.15.203
    • Linux Kernel 6.1.167
    • Linux Kernel 6.6.130
    • Linux Kernel 6.12.78
    • Linux Kernel 6.18.20
    • Linux Kernel 6.19.10
    • Linux Kernel 7.0

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

    Metrics

    7.1

    Priority

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

    Source: NVD, CVSS v3

    7.1

    CVSS v3

    Severity High on the scale from 0 to 10.

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

    0.1 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 2.4

    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
    51.10 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
    7.1 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
    7.1
    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
    2.4
    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
    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: nfnetlink_osf: validate individual option lengths in fingerprints nfnl_osf_add_callback() validates opt_num bounds and string NUL-termination but does not check individual option length fields. A zero-length option causes nf_osf_match_one() to enter the option matching loop even when foptsize sums to zero, which matches packets with no TCP options where ctx->optp is NULL: Oops: general protection fault KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: 0010:nf_osf_match_one (net/netfilter/nfnetlink_osf.c:98) Call Trace: nf_osf_match (net/netfilter/nfnetlink_osf.c:227) xt_osf_match_packet (net/netfilter/xt_osf.c:32) ipt_do_table (net/ipv4/netfilter/ip_tables.c:293) nf_hook_slow (net/netfilter/core.c:623) ip_local_deliver (net/ipv4/ip_input.c:262) ip_rcv (net/ipv4/ip_input.c:573) Additionally, an MSS option (kind=2) with length < 4 causes out-of-bounds reads when nf_osf_match_one() unconditionally accesses optp[2] and optp[3] for MSS value extraction. While RFC 9293 section 3.2 specifies that the MSS option is always exactly 4 bytes (Kind=2, Length=4), the check uses "< 4" rather than "!= 4" because lengths greater than 4 do not cause memory safety issues -- the buffer is guaranteed to be at least foptsize bytes by the ctx->optsize == foptsize check. Reject fingerprints where any option has zero length, or where an MSS option has length less than 4, at add time rather than trusting these values in the packet matching hot path.

    Source: siemens_advisory, Debian LTS Advisories, Debian Security Advisories, suse_csaf, 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
    • 2.6.31 – < 5.10.253
    • 6.2 – < 6.6.130
    • 6.7 – < 6.12.78
    • 6.19 – < 6.19.10
    • 6.13 – < 6.18.20
    • 5.11 – < 5.15.203
    • 6.20 – < 7.0
    • 5.16 – < 6.1.167
    • 5.10.253
    • 6.6.130
    • 6.12.78
    • 6.19.10
    • 6.18.20
    • 5.15.203
    • 7.0
    • 6.1.167
    SiemensSIMATIC S7
    • 1500 TM MFP V1.1.1 GNU/Linux subsystem
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbookworm
    Linuxdebianlinuxbullseye
    Linuxdebianlinuxtrixie
    Linuxdebianlinux-6.1bullseye
    Linuxlinuxlinux_kernel2.6.31
    Linuxlinuxlinux_kernel7.0
    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 24 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
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      https://git.kernel.org/stable/c/224f4678812e1a7bc8341bcb666773a0aec5ea6f
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      https://git.kernel.org/stable/c/3932620c04c2938c93c0890c225960d3d34ba355
      Referenceadded
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      https://git.kernel.org/stable/c/3c11b5c2436a3a5b450612ab160e3a525b28cfb5
      Referenceadded
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      https://git.kernel.org/stable/c/4c6aa008b913e808c4f4d3cde36cb1d9bb5967c6
      Referenceadded
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      https://git.kernel.org/stable/c/aa0574182c46963c3cdb8cde46ec93aca21100d8
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      https://git.kernel.org/stable/c/dbdfaae9609629a9569362e3b8f33d0a20fd783c
      Referenceadded
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      https://git.kernel.org/stable/c/e9cf17b91e733fec725ebcc0b3098bc5ccd505e0
      Referenceadded
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      https://git.kernel.org/stable/c/ec8bf0571b142f29dc0b68ae2ac3952f7a464b38
      Referenceremoved
      https://git.kernel.org/stable/c/224f4678812e1a7bc8341bcb666773a0aec5ea6f
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      Referenceremoved
      https://git.kernel.org/stable/c/3932620c04c2938c93c0890c225960d3d34ba355
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      Referenceremoved
      https://git.kernel.org/stable/c/3c11b5c2436a3a5b450612ab160e3a525b28cfb5
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      Referenceremoved
      https://git.kernel.org/stable/c/4c6aa008b913e808c4f4d3cde36cb1d9bb5967c6
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      Referenceremoved
      https://git.kernel.org/stable/c/aa0574182c46963c3cdb8cde46ec93aca21100d8
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      Referenceremoved
      https://git.kernel.org/stable/c/dbdfaae9609629a9569362e3b8f33d0a20fd783c
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      Referenceremoved
      https://git.kernel.org/stable/c/e9cf17b91e733fec725ebcc0b3098bc5ccd505e0
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      Referenceremoved
      https://git.kernel.org/stable/c/ec8bf0571b142f29dc0b68ae2ac3952f7a464b38
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      Reference typeremoved
      https://git.kernel.org/stable/c/224f4678812e1a7bc8341bcb666773a0aec5ea6f Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/3932620c04c2938c93c0890c225960d3d34ba355 Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/3c11b5c2436a3a5b450612ab160e3a525b28cfb5 Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/4c6aa008b913e808c4f4d3cde36cb1d9bb5967c6 Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/aa0574182c46963c3cdb8cde46ec93aca21100d8 Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/dbdfaae9609629a9569362e3b8f33d0a20fd783c Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/e9cf17b91e733fec725ebcc0b3098bc5ccd505e0 Types: Patch
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      Reference typeremoved
      https://git.kernel.org/stable/c/ec8bf0571b142f29dc0b68ae2ac3952f7a464b38 Types: Patch
      —

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

    2. Record modifiedSiemens ADP

      Show 7 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/2026/23xxx/CVE-2026-23397.json">CVE-2026-23397</a>
      Referenceadded
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      https://cert-portal.siemens.com/productcert/html/ssa-019113.html
      Referenceadded
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      https://cert-portal.siemens.com/productcert/html/ssa-082556.html
      Referenceadded
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      https://cert-portal.siemens.com/productcert/html/ssa-457936.html
      Referenceadded
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      https://cert-portal.siemens.com/productcert/html/ssa-784472.html
      Referenceremoved
      https://cert-portal.siemens.com/productcert/html/ssa-019113.html
      —
      Referenceremoved
      https://cert-portal.siemens.com/productcert/html/ssa-082556.html
      —

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

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