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GHSA-v64f-hrwr-j4vh (https://github.com/flatpak/flatpak/security/advisories/GHSA-v64f-hrwr-j4vh)

Description: A malicious Flatpak application can influence host system behavior beyond its sandbox by including arbitrary keys in its exported Desktop Entry (.desktop) or D-Bus Service (.service) files. This can lead to denial of service (e.g. X-GNOME-AutoRestart causing unconditional application restarts) or unintended interaction with host services (e.g. SystemdService directing the D-Bus daemon to activate a host systemd unit instead of the sandboxed wrapper). When Flatpak exports these files, it rewrites Exec= to go through the flatpak run wrapper and removes a small denylist of known-dangerous keys, but passes all other keys through unmodified. The fix switches from a denylist to an allowlist, exporting only keys from a curated list of known-safe entries.

Mitigation: Only install applications from trusted sources. Patched in 1.18.4 by commit 33931025 ("dir: Validate Desktop Entry and D-Bus Service"). Credit: Reported by Markus Göllnitz.