CVE-2026-97029

Flatpak's process ID namespace separation does not prevent a sandboxed app's kill(0, signal) or killpg(0, signal) calls from reaching processes outside the sandbox that share the same process group. A malicious or compromised Flatpak app can use this to cause denial of service by terminating processes outside its sandbox, such as the desktop shell.

Red Hat estimates the CVSSv3.1 vector of CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H from the upstream CVSSv4.0 vector CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N (score 5.1).

Exploitation requires a victim to install and run a malicious or compromised Flatpak app (UI:R), after which the process-group signal leak is triggered automatically with no additional attacker privileges or access complexity beyond that of a normal sandboxed app (AV:N, AC:L, PR:L). No subsequent system beyond the local host is affected, so scope is unchanged (S:U). There is no confidentiality or integrity impact (C:N, I:N). The availability impact is scored for the reasonable worst case described in the upstream advisory: under common desktop configurations (e.g. GNOME Shell), a malicious app can terminate the desktop shell itself, ending the user's entire session (A:H).

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Run Flatpak apps in a new session (setsid flatpak run ... or setsid() in the parent) or a new process group (setpgid (0, 0) in the parent), or avoid running untrusted Flatpak apps.