HighCVE-2026-31711

    Linux Kernel: security vulnerability (CVE-2026-31711)

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

    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: smb: server: fix active_num_conn leak on transport allocation failure Commit 77ffbcac4e56 ("smb: server: fix leak of active_num_conn in ksmbd_tcp_new_connection()") addressed the kthread_run() failure path. The earlier alloc_transport() == NULL path in the same function has the same leak, is reachable pre-authentication via any TCP connect to port 445, and was empirically reproduced on UML (ARCH=um, v7.0-rc7): a small number of forced allocation failures were sufficient to put ksmbd into a state where every subsequent connection attempt was rejected for the remainder of the boot. ksmbd_kthread_fn() increments active_num_conn before calling ksmbd_tcp_new_connection() and discards the return value, so when alloc_transport() returns NULL the socket is released and -ENOMEM returned without decrementing the counter.

    Update Linux Kernel to version 5.15.210, Linux Kernel to version 6.1.175, Linux Kernel to version 6.6.136.

    Affected
    • Linux Kernel lt 5.15.91..5.15.210
    • Linux Kernel lt 6.1.9..6.1.175
    • Linux Kernel lt 6.2..6.6.136
    • Linux Kernel lt 6.7..6.12.84
    • Linux Kernel lt 6.13..6.18.25
    • Linux Kernel lt 6.19..7.0.2
    Fixed in
    • Linux Kernel 5.15.210
    • Linux Kernel 6.1.175
    • Linux Kernel 6.6.136
    • Linux Kernel 6.12.84
    • Linux Kernel 6.18.25
    • Linux Kernel 7.0.2
    • Linux Kernel 7.1

    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: NVD, CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

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

    0.5 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 46.2

    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
    71.43 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
    46.2
    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

    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: smb: server: fix active_num_conn leak on transport allocation failure Commit 77ffbcac4e56 ("smb: server: fix leak of active_num_conn in ksmbd_tcp_new_connection()") addressed the kthread_run() failure path. The earlier alloc_transport() == NULL path in the same function has the same leak, is reachable pre-authentication via any TCP connect to port 445, and was empirically reproduced on UML (ARCH=um, v7.0-rc7): a small number of forced allocation failures were sufficient to put ksmbd into a state where every subsequent connection attempt was rejected for the remainder of the boot. ksmbd_kthread_fn() increments active_num_conn before calling ksmbd_tcp_new_connection() and discards the return value, so when alloc_transport() returns NULL the socket is released and -ENOMEM returned without decrementing the counter. Each such failure permanently consumes one slot from the max_connections pool; once cumulative failures reach the cap, atomic_inc_return() hits the threshold on every subsequent accept and every new connection is rejected. The counter is only reset by module reload. An unauthenticated remote attacker can drive the server toward the memory pressure that makes alloc_transport() fail by holding open connections with large RFC1002 lengths up to MAX_STREAM_PROT_LEN (0x00FFFFFF); natural transient allocation failures on a loaded host produce the same drift more slowly. Mirror the existing rollback pattern in ksmbd_kthread_fn(): on the alloc_transport() failure path, decrement active_num_conn gated on server_conf.max_connections. Repro details: with the patch reverted, forced alloc_transport() NULL returns leaked counter slots and subsequent connection attempts -- including legitimate connects issued after the forced-fail window had closed -- were all rejected with "Limit the maximum number of connections". With this patch applied, the same connect sequence produces no rejections and the counter cycles cleanly between zero and one on every accept.

    Source: Debian LTS Advisories, Ubuntu Security Notices, siemens_advisory, ENISA EUVD, cvelistv5, NVD (NIST), Microsoft Security Update Guide, CVE.org (MITRE), 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
    • 6.2 – < 6.6.136
    • 6.13 – < 6.18.25
    • 6.7 – < 6.12.84
    • 5.15.91 – < 5.15.210
    • —
    • 6.19 – < 7.0.2
    • 6.1.9 – < 6.1.175
    • 6.6.136
    • 6.18.25
    • 6.12.84
    • 5.15.210
    • 7.1
    • 7.0.2
    • 6.1.175
    MicrosoftAzure Linux
    • azl3
    • —
    SiemensSIMATIC S7
    • 1500 TM MFP V1.1.1 GNU/Linux subsystem
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbookworm
    Linuxdebianlinux-6.1bullseye
    Linuxubuntulinux-gcp-5.15focal
    Linuxlinuxlinux_kernel6.2
    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 19 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/283027aa93380380a0994f35dde3ec95318f2654
      Referenceadded
      —
      https://git.kernel.org/stable/c/295a9fc6789d1011c36ded9f0f2907bb34fa0de4
      Referenceadded
      —
      https://git.kernel.org/stable/c/60734c8bc3b4aa0672e251f08dda81977e4b5387
      Referenceadded
      —
      https://git.kernel.org/stable/c/6551300dc452ac16a855a83dbd1e74899542d3b3
      Referenceadded
      —
      https://git.kernel.org/stable/c/97f8d2648ef4871e4cd335e2d769cb40054a6772
      Referenceadded
      —
      https://git.kernel.org/stable/c/dc2e7d595d68cf1be1ba64e3d30ebf3266bf7242
      Referenceadded
      —
      https://git.kernel.org/stable/c/fb48185bcd946d42de7017cf27f912f8ab26acf0
      Referenceremoved
      https://git.kernel.org/stable/c/283027aa93380380a0994f35dde3ec95318f2654
      —
      Referenceremoved
      https://git.kernel.org/stable/c/295a9fc6789d1011c36ded9f0f2907bb34fa0de4
      —
      Referenceremoved
      https://git.kernel.org/stable/c/60734c8bc3b4aa0672e251f08dda81977e4b5387
      —
      Referenceremoved
      https://git.kernel.org/stable/c/6551300dc452ac16a855a83dbd1e74899542d3b3
      —
      Referenceremoved
      https://git.kernel.org/stable/c/97f8d2648ef4871e4cd335e2d769cb40054a6772
      —
      Referenceremoved
      https://git.kernel.org/stable/c/dc2e7d595d68cf1be1ba64e3d30ebf3266bf7242
      —
      Referenceremoved
      https://git.kernel.org/stable/c/fb48185bcd946d42de7017cf27f912f8ab26acf0
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/283027aa93380380a0994f35dde3ec95318f2654 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/295a9fc6789d1011c36ded9f0f2907bb34fa0de4 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/6551300dc452ac16a855a83dbd1e74899542d3b3 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/97f8d2648ef4871e4cd335e2d769cb40054a6772 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/fb48185bcd946d42de7017cf27f912f8ab26acf0 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/2026/31xxx/CVE-2026-31711.json">CVE-2026-31711</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-784472.html

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

    3. Record modifiedLinux

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://git.kernel.org/stable/c/dc2e7d595d68cf1be1ba64e3d30ebf3266bf7242
      Affected versions (publisher)changed
      Linux, Linux
      Linux, Linux

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

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