A flatpak security update has been released for Debian GNU/Linux 11 to address an issue where sandbox restrictions could be bypassed by manipulating the VFS using mount-related syscalls.

DSA 4984-1: flatpak security update

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Debian Security Advisory DSA-4984-1 security@debian.org
  https://www.debian.org/security/ Salvatore Bonaccorso
October 12, 2021   https://www.debian.org/security/faq
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Package : flatpak
CVE ID : CVE-2021-41133
Debian Bug : 995935

It was discovered that sandbox restrictions in Flatpak, an application
deployment framework for desktop apps, could be bypassed for a Flatpak
app with direct access to AF_UNIX sockets, by manipulating the VFS using
mount-related syscalls that are not blocked by Flatpak's denylist
seccomp filter.

Details can be found in the upstream advisory at
  https://github.com/flatpak/flatpak/security/advisories/GHSA-67h7-w3jq-vh4q

For the stable distribution (bullseye), this problem has been fixed in
version 1.10.5-0+deb11u1.

We recommend that you upgrade your flatpak packages.

For the detailed security status of flatpak please refer to its security
tracker page at:
  https://security-tracker.debian.org/tracker/flatpak

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://www.debian.org/security/