Flatpak’s use of process ID namespace separation fails to block a sandboxed application’s kill(0, signal) or killpg(0, signal) commands from affecting processes that share the same process group outside the sandbox. A malicious or compromised Flatpak bundle can therefore terminate unsandboxed processes such as the desktop shell, causing a denial of service for the end‑user. The weakness responsible for this behavior is identified as CWE‑653.

Red Hat Enterprise Linux 10, 7, 8, and 9 systems that deploy Flatpak applications are impacted. The flaw resides in Flatpak’s sandboxing mechanism on these distributions.

The CVSS score of 5.7 denotes moderate severity. The EPSS score is not disclosed, and the vulnerability is not catalogued in CISA’s KEV. The likely attack vector is local: a user running a malicious or compromised Flatpak app can exploit the flaw without elevated privileges by sending a termination signal to the shared process group, leading to a denial of service that can shut down essential desktop components.