CVE-2025-21703

Local privilege escalation via stale DRR active-list entry

Published Feb 18, 2025 · Updated Aug 5, 2026

Use-after-free in Linux kernel netem allows local users to escalate privileges through a crafted netem and DRR qdisc interaction. netem calls qdisc_tree_reduce_backlog() before reducing its child queue length, so DRR misses qlen_notify() and retains a freed class on its active list. Exploitation requires low-privileged local access and unprivileged user namespaces; successful exploitation grants elevated kernel privileges.

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

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Use-after-free in Linux kernel netem allows local users to escalate privileges through a crafted netem and DRR qdisc interaction. netem calls qdisc_tree_reduce_backlog() before reducing its child queue length, so DRR misses qlen_notify() and retains a freed class on its active list. Exploitation requires low-privileged local access and unprivileged user namespaces; successful exploitation grants elevated kernel privileges.

The record

CVE
CVE-2025-21703
Published
Feb 18, 2025
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 18, 2025CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=10df49cfca73dfbbdb6c4150d859f7e8926ae427 <7b79ca9a1de6a428d486ff52fb3d602321c08f55
  2. Affected versionversion=216509dda290f6db92c816dd54b83c1df9da9e76 <7f31d74fcc556a9166b1bb20515542de7bb939d1
  3. Affected versionversion=356078a5c55ec8d2061fcc009fb8599f5b0527f9 <6312555249082d6d8cc5321ff725df05482d8b83
  4. Affected versionversion=3824c5fad18eeb7abe0c4fc966f29959552dca3e <1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5
  5. Affected versionversion=5.10.232 <5.10.235
  6. Affected versionversion=5.15.175 <5.15.179
  7. Affected versionversion=5.4.288 <5.4.291
  8. Affected versionversion=6.1.121 <6.1.129
  9. Affected versionversion=6.12.6 <6.12.14
  10. Affected versionversion=6.13
  11. Affected versionversion=6.6.67 <6.6.78
  12. Affected versionversion=83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31 <e395fec75ac2dbffc99b4bce57b7f1f3c5449f2c
  13. Affected versionversion=c2047b0e216c8edce227d7c42f99ac2877dad0e4 <98a2c685293aae122f688cde11d9334dddc5d207
  14. Affected versionversion=f8d4bc455047cf3903cd6f85f49978987dbb3027 <638ba5089324796c2ee49af10427459c2de35f71
  15. Affected versionversion=f8d4bc455047cf3903cd6f85f49978987dbb3027 <839ecc583fa00fab785fde1c85a326743657fd32

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=10df49cfca73dfbbdb6c4150d859f7e8926ae427 <7b79ca9a1de6a428d486ff52fb3d602321c08f55; version=216509dda290f6db92c816dd54b83c1df9da9e76 <7f31d74fcc556a9166b1bb20515542de7bb939d1; version=356078a5c55ec8d2061fcc009fb8599f5b0527f9 <6312555249082d6d8cc5321ff725df05482d8b83; version=3824c5fad18eeb7abe0c4fc966f29959552dca3e <1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5; version=5.10.232 <5.10.235; version=5.15.175 <5.15.179; version=5.4.288 <5.4.291; version=6.1.121 <6.1.129; version=6.12.6 <6.12.14; version=6.13; version=6.6.67 <6.6.78; version=83c6ab12f08dcc09d4c5ac86fdb89736b28f1d31 <e395fec75ac2dbffc99b4bce57b7f1f3c5449f2c; version=c2047b0e216c8edce227d7c42f99ac2877dad0e4 <98a2c685293aae122f688cde11d9334dddc5d207; version=f8d4bc455047cf3903cd6f85f49978987dbb3027 <638ba5089324796c2ee49af10427459c2de35f71; version=f8d4bc455047cf3903cd6f85f49978987dbb3027 <839ecc583fa00fab785fde1c85a326743657fd32

Published CVSS scores

7.8Linux CNACVSS: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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo