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Fencer Intel
medium 5.5

CVE-2021-27851 json

Local privilege escalation in GNU Guix via guix-daemon and '--keep-failed'

published 5y ago modified 4mo ago also EUVD-2021-14589

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 26%
public exploits
0
none known

Summary

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.

Patch / fix

  • GNU Guix guix-daemon v1.2.0-75109-g94f0312546
  • guix Debian 11 1.2.0-4

debian advisories DEBIAN-CVE-2021-27851

  • guix openSUSE Tumbleweed 1.3.0-1.8

opensuse advisories openSUSE-SU-2024:10836-1

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Exploit prediction

0.33% chance of exploitation in the next 30 days, higher than 26% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
NVD 2.0 2.1 AV:L/AC:L/Au:N/C:N/I:P/A:N

Affected products

  • GNU Guix guix-daemon

Classification

Weakness
  • CWE-264 Permissions, Privileges, and Access Controls
  • CWE-59 Improper Link Resolution Before File Access

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.