CVE-2023-4921

Local privilege escalation via qfq use-after-free

Published Sep 12, 2023 · Updated Feb 25, 2026

Use-after-free in Linux Kernel before 6.6 allows local users to escalate privileges by sending packets through a nested qfq discipline. When a plug qdisc acts as a qfq class, sch_plug supplies an incorrect peek handler and agg_dequeue fails to reject the resulting condition before qfq_dequeue reuses freed state. Reachability requires control of the traffic-control configuration; successful exploitation corrupts kernel memory and elevates the local user's privileges.

CVSS severity7.8
High
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in Linux Kernel before 6.6 allows local users to escalate privileges by sending packets through a nested qfq discipline. When a plug qdisc acts as a qfq class, sch_plug supplies an incorrect peek handler and agg_dequeue fails to reject the resulting condition before qfq_dequeue reuses freed state. Reachability requires control of the traffic-control configuration; successful exploitation corrupts kernel memory and elevates the local user's privileges.

The record

CVE
CVE-2023-4921
Published
Sep 12, 2023
Updated
Feb 25, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-416, CAPEC-233, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 12, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=3.8 <6.6

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=3.8 <6.6

Published CVSS scores

7.8UbuntuCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
CAPEC-233Privilege Escalation
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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