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HIGH

CVE-2023-4921

CVSS v3

7.8

HIGH

EPSS Score

0.4 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • kernelAlmaLinux:8all versions · fixed in 4.18.0-513.18.1.el8_9and 23 other packages
  • linuxUbuntu:23.10all versions · fixed in 6.5.0-10.10
  • linux-awsUbuntu:23.10all versions · fixed in 6.5.0-1009.9
  • linux-gcpUbuntu:23.10all versions · fixed in 6.5.0-1008.8and 1 other package
  • linux-laptopUbuntu:23.10all versions · fixed in 6.5.0-1005.8
  • linux-lowlatencyUbuntu:23.10all versions · fixed in 6.5.0-10.10.1
  • linux-oracleUbuntu:23.10all versions · fixed in 6.5.0-1011.11
  • linux-raspiUbuntu:23.10all versions · fixed in 6.5.0-1006.8

1 more package range on OSV.dev

Vendor advisories

  • CVE-2023-4921 Red Hat Product Security1,099 products fixed

    kernel: use-after-free in sch_qfq network scheduler

  • ICSA-25-044-09 CISA19 known affected

    Siemens SCALANCE W700 IEEE 802.11ax

    SCALANCE WAB762-1 (6GK5762-1AJ00-6AA0) · SCALANCE WAM763-1 (6GK5763-1AL00-7DA0) · SCALANCE WAM763-1 (ME) (6GK5763-1AL00-7DC0)

  • SSA-769027 Siemens ProductCERT19 known affected

    SSA-769027: Multiple Vulnerabilities fixed in SCALANCE W700 IEEE 802.11ax devices before V3.0.0

    SCALANCE WAB762-1 (6GK5762-1AJ00-6AA0) · SCALANCE WAM763-1 (6GK5763-1AL00-7DA0) · SCALANCE WAM763-1 (ME) (6GK5763-1AL00-7DC0)

  • RHSA-2024:1831 Red Hat Product Security56 products fixed

    Red Hat Security Advisory: kernel security update

  • RHSA-2024:1404 Red Hat Product Security120 products fixed

    Red Hat Security Advisory: kernel security and bug fix update

  • RHSA-2024:1368 Red Hat Product Security21 products fixed

    Red Hat Security Advisory: kpatch-patch security update

20 more advisories

Full record on NVD

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.

Technical details

Published
2023-09-12

Frequently asked questions

What is CVE-2023-4921?

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.

Is CVE-2023-4921 actively exploited?

Active exploitation of CVE-2023-4921 has not been confirmed. Its EPSS score was 0.4% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2023-4921?

CVE-2023-4921 has a CVSS v3 base score of 7.8 (HIGH severity).

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