GNU Guix Vulnerabilities Let Attackers Overwrite Arbitrary Files and Escalate Privileges

Security researcher Caleb Ristvedt disclosed the issues on July 222, 202620262026, warning that all GNU Guix installations are affected.

Systems running guix-daemon as root face the highest risk because a malicious substitute server or a man-in-the-middle attacker could write files in root-accessible locations, including /etc/passwd.

GNU Guix Vulnerabilities

The most severe issue affects restore-file, the procedure used to unpack binary substitutes. Guix previously extracted substitute contents while downloading them, before the complete archive hash was verified.

Because the extractor did not adequately validate malicious archive entries, an attacker-controlled substitute source could write arbitrary files wherever the daemon user had permissions.

An attacker only needs access to the target system to attempt to download a substitute. This can occur through configured substitute servers, automatically discovered servers, or a network attacker impersonating a substitute service.

HTTPS does not fully mitigate the problem because metadata processing allowed an attacker to replace a substitute URL before the archive download stage.

A second flaw in the fetch-narinfos routine was that it failed to verify that the returned metadata matched the requested store item. This could allow a malicious substitute server to provide an authorized replacement for another package, potentially forcing Guix to install outdated or vulnerable software.

A third guix substitute weakness allowed untrusted clients to supply file:// URIs as substitute URLs or archive locations. Since ordinary local users can generally connect to the guix-daemon socket, they could potentially make the daemon read files available to its account.

If an accessed file contained malformed narinfo data, Guix could return an exception and backtrace containing portions of the file to the requesting client.

The issue could expose sensitive data, such as a passphrase stored in a readable file. Symbolic link handling and references via /proc/PID/fd could also allow attackers to interfere with files read by traceable daemon-user processes.

Separately, guix pull and guix time-machine contained a path-traversal issue in how they handled the channel authentication cache. A malicious channels file could use a crafted channel name, such as ../../../../newfile, to create or overwrite files that are writable by the command’s user.

The restricted output format makes denial-of-service the most likely impact. However, researchers cautioned that targeting special files in /proc may pose additional risks.

Patches and Mitigation

Guix fixed the issues through 111111 commits in pull request #9665. Users should upgrade to commit 897832f374dcdc9eeaf19d01e70b9a92fccfc68c or later.

As an interim measure to mitigate remote exposure, administrators can turn off substitutes with –no-substitutes. However, this does not protect against local attackers able to access the daemon socket; patching remains essential.

For Guix System, administrators should run:

guix pull
sudo guix system reconfigure /run/current-system/configuration.scm
sudo herd restart guix-daemon

Users on other Linux distributions should update Guix as root and restart the guix-daemon service. Guix also provides a test script, runnable with guix repl — guix-substitute-and-pull-vuln-check.scm, to identify affected installations.

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