A flaw was found in Flatpak. The Flatpak portal D-Bus 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 outside the sandbox. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.