Local privilege escalation via AF_UNIX garbage-collection race
Published Dec 15, 2021 · Updated Oct 21, 2025
A use-after-free in the Linux kernel's AF_UNIX subsystem allows local users with System privileges to escalate privileges. In unix_scm_to_skb, concurrent MSG_PEEK file-reference increments can mislead unix_gc into reclaiming an in-flight sk_buff that remains reachable. Exploitation requires local code execution and a complex multithreaded race, but successful heap shaping yields arbitrary kernel-memory reads and writes without user interaction.
Summary
What happened
A use-after-free in the Linux kernel's AF_UNIX subsystem allows local users with System privileges to escalate privileges. In unix_scm_to_skb, concurrent MSG_PEEK file-reference increments can mislead unix_gc into reclaiming an in-flight sk_buff that remains reachable. Exploitation requires local code execution and a complex multithreaded race, but successful heap shaping yields arbitrary kernel-memory reads and writes without user interaction.
The record
- CVE
- CVE-2021-0920
- Published
- Dec 15, 2021
- Updated
- Oct 21, 2025
- Vendor
- The Linux Kernel Organization
- Product
- Linux Kernel
- Classifications
- CWE-416, CWE-362, T1404
- Attack vector
- local
- Privileges
- admin
Timeline
How it unfolded
- Dec 15, 2021CVE publishedPublication date reported by the CVE source.
- Oct 21, 2025Record 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.
- Affected versionversion=Android kernel
What conditions does exploitation require?
What is affected?
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.
Weakness, pattern, technique
Public exploit references
- Google Project Zero CVE-2021-0920 proof of conceptproof of concept · demonstrated
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Reported exploitation
- Limited targeted exploitation reported by Androidreported exploitation
- Samsung full-chain exploitationexploit chain
Technologies
Your stack
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Your stack
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