Prior to version 1.22.1, sandboxed applications can invoke the FileChooser.SaveFiles method of the XDG Desktop Portal to specify arbitrary filenames. Because the frontend does not validate these names and backends rely on an existence check that is not performed, an attacker can request files that do not yet exist and the portal will attempt to create them in a user‑specified directory. This allows the creation or modification of any file that the logged‑in user can access, effectively giving the sandboxed app the same file‑system privileges as the host user. The weakness is a path traversal flaw (CWE‑22).

The affected product is the Flatpak XDG Desktop Portal. Versions earlier than 1.22.1 are vulnerable; the issue was fixed in 1.22.1.

The CVSS score is 8.8, indicating high severity. EPSS is not available, and the vulnerability is not listed in CISA KEV. The most probable attack vector involves a malicious sandboxed application exploiting the FileChooser.SaveFiles API; no special network or privileged access is required beyond the ability to run a sandboxed app. Once the path traversal succeeds, the attacker can create arbitrary files in the target’s directory space.