Simon McVittie discovered a bug in the flatpak-portal service that can
allow sandboxed applications to execute arbitrary code on the host system
(a sandbox escape).
The Flatpak portal D-Bus service (flatpak-portal, also known by its
D-Bus service name org.freedesktop.portal.Flatpak) allows apps in a
Flatpak sandbox to launch their own subprocesses in a new sandbox
instance, either with the same security settings as the caller or
with more restrictive security settings. For example, this is used in Flatpak-packaged web browsers such as Chromium to launch subprocesses
that will process untrusted web content, and give those subprocesses a
more restrictive sandbox than the browser itself.
In vulnerable versions, the Flatpak portal service passes caller-specified environment variables to non-sandboxed processes on the host system,
and in particular to the flatpak run command that is used to launch the
new sandbox instance. A malicious or compromised Flatpak app could set environment variables that are trusted by the flatpak run command, and
use them to execute arbitrary code that is not in a sandbox.
For the stable distribution (buster), this problem has been fixed in
We recommend that you upgrade your flatpak packages.