Subject: [ASA-202101-40] flatpak: sandbox escape

Arch Linux Security Advisory ASA-202101-40
==========================================

Severity: High
Date    : 2021-01-20
CVE-ID  : CVE-2021-21261
Package : flatpak
Type    : sandbox escape
Remote  : No
Link    : https://security.archlinux.org/AVG-1454

Summary
=======

The package flatpak before version 1.10.0-1 is vulnerable to sandbox
escape.

Resolution
==========

Upgrade to 1.10.0-1.

# pacman -Syu "flatpak>=1.10.0-1"

The problem has been fixed upstream in version 1.10.0.

Workaround
==========

None.

Description
===========

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 the 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.

Impact
======

A malicious application could execute arbitrary code on the host.

References
==========

https://github.com/flatpak/flatpak/security/advisories/GHSA-4ppf-fxf6-vxg2
https://github.com/flatpak/flatpak/commit/6d1773d2a54dde9b099043f07a2094a4f1c2f486
https://github.com/flatpak/flatpak/commit/821249844bbb7e52cbf4508b4de18c05e8592220
https://github.com/flatpak/flatpak/commit/6e5ae7a109cdfa9735ea7ccbd8cb79f9e8d3ae8b
https://github.com/flatpak/flatpak/commit/aeb6a7ab0abaac4a8f4ad98b3df476d9de6b8bd4
https://github.com/flatpak/flatpak/commit/39a5621e6941b9d27bf89b63e8fb6cad6e279e53
https://github.com/flatpak/flatpak/commit/cc1401043c075268ecc652eac557ef8076b5eaba
https://github.com/flatpak/flatpak/commit/d19f6c330aa42e17df6dc36d12b6f4dfa507dbb3
https://security.archlinux.org/CVE-2021-21261