CVE-2021-27851

What it is

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.

At a glance

Exploitability

Can be exploited locally on the machine with a low-privilege account. High risk of data tampering.

Exploit odds

0.3% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-04-26 16:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:45 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.3% in the next 30 days (EPSS).
• Severity: 5.5 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-04-26 16:15 UTC

Last modified

2026-06-17 03:45 UTC

Exploit probability

0.3% · EPSS, next 30 days

Weakness

CWE-264

Record status

Modified

Affected

• Gnu Guix < 1.2.0

Attack profile CVSS 3.1 · 5.5

Attack vector

Local

Complexity

Low

Privileges needed

Low

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-27851.md and follow it. Check whether this project is affected by CVE-2021-27851. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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