GNU nano versions before 9.0 improperly assign permissions when creating the ~/.local directory, explicitly requesting mode 0777, which results in world-writable permissions if the system umask does not restrict them. This incorrect permission assignment (CWE-732) can be exploited locally to write attacker-controlled files during a race window before nano creates more restrictive subdirectories. The vulnerability affects nano version 2.9.1 and was published on 2026-04-28. No official patch link or remediation level is provided in the data, but the issue is fixed in nano 9.0.

On systems with relaxed or zero umask settings, such as containers, CI/CD runners, embedded systems, or user shells configured with umask 000, the ~/.local directory becomes world-writable. This allows a local attacker to exploit a race condition to insert malicious files into the victim's XDG directory hierarchy, potentially leading to unauthorized file manipulation. The impact is limited to local privilege and file integrity issues and is rated as low severity (CVSS 2.1).

Upgrade GNU nano to version 9.0 or later, where this permission assignment issue is fixed. Since no official patch link or vendor advisory is provided, users should verify the nano version in use and update accordingly. In the meantime, ensure that system umask settings are not overly permissive (avoid umask 000) to reduce exposure.