CVE-2021-21261

Flatpak is a system for building, distributing, and running sandboxed
desktop applications on Linux. A bug was discovered in the flatpak-portal
service that can allow sandboxed applications to execute arbitrary code on
the host system (a sandbox escape). This sandbox-escape bug is present in
versions from 0.11.4 and before fixed versions 1.8.5 and 1.10.0. 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. As a workaround, this vulnerability can be mitigated by
preventing the flatpak-portal service from starting, but that mitigation
will prevent many Flatpak apps from working correctly. This is fixed in
versions 1.8.5 and 1.10.0.

Bugs

• <https://bugs.launchpad.net/bugs/1911473&gt;