XDG Desktop Portal CVE-2026-55889

Requires a malicious or compromised sandboxed application (e.g. a hostile Flatpak) already running on the victim's desktop that can invoke the FileTransfer.RetrieveFiles portal method. The attacker must generate enough tokens to recover the state of GLib's GRand (Mersenne Twister) PRNG seeded via g_random_int / g_uuid_string_random, then predict the next token that normally authorizes an out-of-band resource transfer; a victim drag-and-drop or copy-paste operation must occur for data to be redirected. Limiting factors: the attacker needs an execution foothold inside the sandbox on the host (not purely remote network access despite the AV:N vector), token-state recovery adds complexity (AC:H), and only versions <=1.22.0 are affected. Mitigation per the vendor is updating to 1.22.1; no other known mitigation exists.

This is a legitimate, prioritizable weakness but not an emergency. The vendor CVSS 4.0 score is 8.3 (High) with VC:H reflecting theft of potentially sensitive clipboard and drag-and-drop content. The decision label is 'this_week', consistent with a serious-but-not-critical issue. Key signals are missing or in tension: no EPSS probability is provided, there is no CISA KEV listing (not actively exploited), and no public exploit code is referenced - only the vendor advisory and release tag. The most important caveat is an attack-vector tension: the vendor vector is AV:N, but the mechanism described is a malicious sandboxed application already running on the victim's desktop that abuses the FileTransfer D-Bus interface, which is effectively local presence on the host - verify the AV:N choice with the vendor, as it reads more like local/adjacent access. AC:H is consistent with the real work required (generating enough tokens to recover the GRand PRNG state), which raises the practical bar. Overall: a real, patch-worthy data-confidentiality flaw whose exploitation presupposes attacker code already running in a sandbox on the machine, so widespread opportunistic exploitation is unlikely.

A user installs a malicious or compromised Flatpak application that runs inside the normal xdg-desktop-portal sandbox. The app repeatedly requests FileTransfer tokens to recover the internal state of GLib's Mersenne Twister PRNG, then predicts the token another application will use, and calls FileTransfer.RetrieveFiles to redirect a legitimate drag-and-drop or copy-paste transfer to itself, stealing the files. No public exploit code is referenced in the available data; the attack requires some complexity (AC:H) to recover the PRNG state.