Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. in versions before 1.10.9, 1.12.9, 1.14.6, and 1.15.8, a malicious or compromised Flatpak app could execute arbitrary code outside its sandbox. Normally, the `--command` argument of `flatpak run` expects to be given a command to run in the specified Flatpak app, optionally along with some arguments. However it is possible to instead pass `bwrap` arguments to `--command=`, such as `--bind`. It's possible to pass an arbitrary `commandline` to the portal interface `org.freedesktop.portal.Background.RequestBackground` from within a Flatpak app. When this is converted into a `--command` and arguments, it achieves the same effect of passing arguments directly to `bwrap`, and thus can be used for a sandbox escape. The solution is to pass the `--` argument to `bwrap`, which makes it stop processing options. This has been supported since bubblewrap 0.3.0. All supported versions of Flatpak require at least that version of bubblewrap. xdg-desktop-portal version 1.18.4 will mitigate this vulnerability by only allowing Flatpak apps to create .desktop files for commands that do not start with --. The vulnerability is patched in 1.15.8, 1.10.9, 1.12.9, and 1.14.6.

https://github.com/flatpak/flatpak/commit/72016e3fce8fcbeab707daf4f1a02b931fcc004d
https://github.com/flatpak/flatpak/commit/81abe2a37d363f5099c3d0bdcd0caad6efc5bf97
https://github.com/flatpak/flatpak/commit/b7c1a558e58aaeb1d007d29529bbb270dc4ff11e
https://github.com/flatpak/flatpak/commit/bbab7ed1e672356d1a78b422462b210e8e875931
https://github.com/flatpak/flatpak/security/advisories/GHSA-phv6-cpc2-2fgj