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Back to active CVEs
High · CVSS 7.8CVE-2023-4921

Use-after-free in Linux kernel's net/sched: sch_qfq componentCVE-2023-4921

Answer in brief

CVE-2023-4921 records a High severity (CVSS 7.8) vulnerability in Use-after-free in Linux kernel's net/sched: sch_qfq component. The current sources do not mark it as known exploited. The current feed maps Linux/Kernel (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 TM MFP - GNU/Linux subsystem (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 12, 2023Updated Oct 14, 2026Source checked Oct 14, 2026First seen by HOL Oct 14, 2026Material review Oct 14, 2026
Upstream Advisory

Key facts

Risk
High · CVSS 7.8
Exploitation
Not marked as known exploited
Affected software
5 mapped packages or products
Fix availability
Available

Why this deserves its current priority

CVSS is 7.8. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Kernel (generic), Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (generic), Siemens/SIMATIC S7-1500 TM MFP - GNU/Linux subsystem (generic) and additional mapped packages. Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
PackageAffected rangeFixed version
Linux/Kernelgeneric>=3.8 <6.66.6
Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFPgeneric>=V3.1.0 <V3.1.5V3.1.5
Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPgeneric>=V3.1.0 <V3.1.5V3.1.5
Siemens/SIMATIC S7-1500 TM MFP - GNU/Linux subsystemgeneric>=0 <V1.1V1.1
Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFPgeneric>=V3.1.0 <V3.1.5V3.1.5

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for Linux/Kernel, Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP.
  2. 2Review the reported fix. Update Linux/Kernel to 6.6; Siemens/SIMATIC S7-1500 CPU 1518-4 PN/DP MFP to V3.1.5; Siemens/SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP to V3.1.5; Siemens/SIMATIC S7-1500 TM MFP - GNU/Linux subsystem to V1.1; Siemens/SIPLUS S7-1500 CPU 1518-4 PN/DP MFP to V3.1.5 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

  1. Published upstream

    Sep 12, 2023

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Oct 14, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Oct 14, 2026

Sources and claim methodology

  • Source referencecert-portal.siemens.com
  • Source referencecert-portal.siemens.com
  • Source referencecert-portal.siemens.com
  • Source referencegit.kernel.org
  • Source referencekernel.dance
  • Source referencelists.debian.org
  • Source referencelists.debian.org
Upstream source description

A use-after-free vulnerability in the Linux kernel's net/sched: sch_qfq component can be exploited to achieve local privilege escalation. When the plug qdisc is used as a class of the qfq qdisc, sending network packets triggers use-after-free in qfq_dequeue() due to the incorrect .peek handler of sch_plug and lack of error checking in agg_dequeue(). We recommend upgrading past commit 8fc134fee27f2263988ae38920bc03da416b03d8.

Quoted source text, attributed separately from HOL analysis.

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Record context

Vulnerability class
Memory Corruption
EPSS
Not reported
CWE IDs
CWE-416
Source
CVE List V5
Source checked
Oct 14, 2026
References
7 linked sources
Open source record