How severe is CVE-2021-27851?

CVE-2021-27851 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2021-27851 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (25th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-27851?

CVE-2021-27851 affects Gnu Guix. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-27851?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-27851 published?

CVE-2021-27851 was published on 2021-04-26 and last updated on 2026-06-17.

CVE-2021-27851

CVE-2021-27851 is a medium-severity vulnerability in Gnu Guix with a CVSS 3.x base score of 5.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-59.

Key facts

Severity: Medium (CVSS 3.x base score 5.5)
CVSS v2: 2.1
EPSS exploit prediction: 0% (25th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-59
Affected product: Gnu Guix
Published: 2021-04-26
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-27851?: 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.
How severe is CVE-2021-27851?: CVE-2021-27851 has a CVSS 3.x base score of 5.5, rated medium severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2021-27851 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (25th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-27851?: CVE-2021-27851 affects Gnu Guix. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-27851?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-27851 published?: CVE-2021-27851 was published on 2021-04-26 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:gnu:guix:*:*:*:*:*:*:*:*

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