Description

CERT Polska has received a report about vulnerability in GNU nano software and participated in coordination of its disclosure.

The vulnerability CVE-2026-40556: GNU nano creates the user’s ~/.local directory with overly permissive permissions when the directory does not exist yet. On first use of features requiring Cross-Desktop Group (XDG) data storage, nano explicitly requests directory mode 0777, making the directory world‑writable in environments where the process umask does not sufficiently restrict permissions. In systems with a relaxed or zero umask, such as container environments, CI/CD runners, embedded systems, or user shells configured with umask 000, this results in ~/.local being created as world‑writable. A local attacker can exploit a race window between nano’s creation of ~/.local and its subsequent creation of more restrictive subdirectories to write attacker‑controlled files into the victim’s XDG directory hierarchy.

This problem was fixed in nano version 9.0

Credits

We thank Michal Majchrowicz (AFINE) and Marcin Wyczechowski (AFINE) for the responsible vulnerability report.