HighCVE-2025-21702

    Linux Kernel: Privilege Escalation (CVE-2025-21702)

    Published Last modified Sources: Siemens ProductCERT, SUSE, BSI, Debian LTS, Red Hat, Debian, CVE.org, EUVD

    What is affected, what to do

    In the Linux kernel, the following vulnerability has been resolved: pfifo_tail_enqueue: Drop new packet when sch->limit == 0 Expected behaviour: In case we reach scheduler's limit, pfifo_tail_enqueue() will drop a packet in scheduler's queue and decrease scheduler's qlen by one. Then, pfifo_tail_enqueue() enqueue new packet and increase scheduler's qlen by one.

    Update Linux Kernel to version 5.4.291, Linux Kernel to version 5.10.235, Linux Kernel to version 5.15.179.

    Affected
    • Linux Kernel lt 2.6.34..5.4.291
    • Linux Kernel lt 5.5..5.10.235
    • Linux Kernel lt 5.11..5.15.179
    • Linux Kernel lt 5.16..6.1.130
    • Linux Kernel lt 6.2..6.6.83
    • Linux Kernel lt 6.7..6.12.14
    • Linux Kernel lt 6.13..6.13.3
    Fixed in
    • Linux Kernel 5.4.291
    • Linux Kernel 5.10.235
    • Linux Kernel 5.15.179
    • Linux Kernel 6.1.130
    • Linux Kernel 6.6.83
    • Linux Kernel 6.12.14
    • Linux Kernel 6.13.3
    • Linux Kernel 6.14

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

    Metrics

    7.8

    Priority

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

    Source: Vendor (CNA), CVSS v3

    7.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Siemens ProductCERT, SUSE, BSI, Debian LTS, Red Hat, Debian, CVE.org, EUVD

    0.3 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 20.8

    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
    50.35 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
    7.8 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
    7.8
    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
    0.3 %
    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
    20.8
    Elevated — this CVE ranks above at least 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: pfifo_tail_enqueue: Drop new packet when sch->limit == 0 Expected behaviour: In case we reach scheduler's limit, pfifo_tail_enqueue() will drop a packet in scheduler's queue and decrease scheduler's qlen by one. Then, pfifo_tail_enqueue() enqueue new packet and increase scheduler's qlen by one. Finally, pfifo_tail_enqueue() return `NET_XMIT_CN` status code. Weird behaviour: In case we set `sch->limit == 0` and trigger pfifo_tail_enqueue() on a scheduler that has no packet, the 'drop a packet' step will do nothing. This means the scheduler's qlen still has value equal 0. Then, we continue to enqueue new packet and increase scheduler's qlen by one. In summary, we can leverage pfifo_tail_enqueue() to increase qlen by one and return `NET_XMIT_CN` status code. The problem is: Let's say we have two qdiscs: Qdisc_A and Qdisc_B. - Qdisc_A's type must have '->graft()' function to create parent/child relationship. Let's say Qdisc_A's type is `hfsc`. Enqueue packet to this qdisc will trigger `hfsc_enqueue`. - Qdisc_B's type is pfifo_head_drop. Enqueue packet to this qdisc will trigger `pfifo_tail_enqueue`. - Qdisc_B is configured to have `sch->limit == 0`. - Qdisc_A is configured to route the enqueued's packet to Qdisc_B. Enqueue packet through Qdisc_A will lead to: - hfsc_enqueue(Qdisc_A) -> pfifo_tail_enqueue(Qdisc_B) - Qdisc_B->q.qlen += 1 - pfifo_tail_enqueue() return `NET_XMIT_CN` - hfsc_enqueue() check for `NET_XMIT_SUCCESS` and see `NET_XMIT_CN` => hfsc_enqueue() don't increase qlen of Qdisc_A. The whole process lead to a situation where Qdisc_A->q.qlen == 0 and Qdisc_B->q.qlen == 1. Replace 'hfsc' with other type (for example: 'drr') still lead to the same problem. This violate the design where parent's qlen should equal to the sum of its childrens'qlen. Bug impact: This issue can be used for user->kernel privilege escalation when it is reachable.

    Source: siemens_advisory, suse_csaf, BSI WID Portal, BSI CSAF, Debian LTS Advisories, redhat_csaf, Debian Security Advisories, cvelistv5, NVD (NIST), CVE.org (MITRE), 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
    • 5.5 – < 5.10.235
    • 6.2 – < 6.6.83
    • 5.16 – < 6.1.130
    • —
    • 2.6.34 – < 5.4.291
    • 5.11 – < 5.15.179
    • 6.7 – < 6.12.14
    • 6.13 – < 6.13.3
    • 5.10.235
    • 6.6.83
    • 6.1.130
    • 6.14
    • 5.4.291
    • 5.15.179
    • 6.12.14
    • 6.13.3
    DellSecure Connect Gateway Appliance
    • < 5.32.00.18
    • 5.32.00.18
    IBMSecurity Verify Access
    • < 10.0.9.2
    • 10.0.9.2
    Open SourceLinux Kernel
    • < 6.6.78
    • < 6.14-rc2
    • < 6.12.14
    • < 6.13.3
    • 6.6.78
    • 6.14-rc2
    • 6.12.14
    • 6.13.3
    SiemensSIMATIC S7
    • 1500 CPU
    • 1500 TM MFP V1.1.1 GNU/Linux subsystem
    • —
    • —
    SolarWindsSecurity Event Manager
    • < 2025.2.1
    • 2025.2.1

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlinuxbookworm
    Linuxdebianlinuxbullseye
    Linuxdebianlinux-6.1bullseye
    Linuxlinuxlinux_kernel6.14
    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
      —
      https://git.kernel.org/stable/c/020ecb76812a0526f4130ab5aeb6dc7c773e7ab9
      Referenceadded
      —
      https://git.kernel.org/stable/c/647cef20e649c576dff271e018d5d15d998b629d
      Referenceadded
      —
      https://git.kernel.org/stable/c/78285b53266d6d51fa4ff504a23df03852eba84e
      Referenceadded
      —
      https://git.kernel.org/stable/c/79a955ea4a2e5ddf4a36328959de0de496419888
      Referenceadded
      —
      https://git.kernel.org/stable/c/7a9723ec27aff5674f1fd4934608937f1d650980
      Referenceadded
      —
      https://git.kernel.org/stable/c/a56a6e8589a9b98d8171611fbcc1e45a15fd2455
      Referenceadded
      —
      https://git.kernel.org/stable/c/b6a079c3b6f95378f26e2aeda520cb3176f7067b
      Referenceadded
      —
      https://git.kernel.org/stable/c/e40cb34b7f247fe2e366fd192700d1b4f38196ca
      Referenceremoved
      https://git.kernel.org/stable/c/020ecb76812a0526f4130ab5aeb6dc7c773e7ab9
      —
      Referenceremoved
      https://git.kernel.org/stable/c/647cef20e649c576dff271e018d5d15d998b629d
      —
      Referenceremoved
      https://git.kernel.org/stable/c/78285b53266d6d51fa4ff504a23df03852eba84e
      —
      Referenceremoved
      https://git.kernel.org/stable/c/79a955ea4a2e5ddf4a36328959de0de496419888
      —
      Referenceremoved
      https://git.kernel.org/stable/c/7a9723ec27aff5674f1fd4934608937f1d650980
      —
      Referenceremoved
      https://git.kernel.org/stable/c/a56a6e8589a9b98d8171611fbcc1e45a15fd2455
      —
      Referenceremoved
      https://git.kernel.org/stable/c/b6a079c3b6f95378f26e2aeda520cb3176f7067b
      —
      Referenceremoved
      https://git.kernel.org/stable/c/e40cb34b7f247fe2e366fd192700d1b4f38196ca
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/020ecb76812a0526f4130ab5aeb6dc7c773e7ab9 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/647cef20e649c576dff271e018d5d15d998b629d Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/78285b53266d6d51fa4ff504a23df03852eba84e Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/79a955ea4a2e5ddf4a36328959de0de496419888 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/7a9723ec27aff5674f1fd4934608937f1d650980 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/a56a6e8589a9b98d8171611fbcc1e45a15fd2455 Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/b6a079c3b6f95378f26e2aeda520cb3176f7067b Types: Patch
      —
      Reference typeremoved
      https://git.kernel.org/stable/c/e40cb34b7f247fe2e366fd192700d1b4f38196ca Types: Patch
      —

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

    2. Record modifiedCVE Program

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
      Referenceadded
      —
      https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html
      Referenceremoved
      https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
      —
      Referenceremoved
      https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html
      —

      Source identifier: af854a3a-2127-422b-91ae-364da2661108

    3. 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/2025/21xxx/CVE-2025-21702.json">CVE-2025-21702</a>
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-019113.html
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-082556.html
      Referenceadded
      —
      https://cert-portal.siemens.com/productcert/html/ssa-457936.html
      Referenceadded
      —
      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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