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.
Flatpak before 1.0.8, 1.1.x and 1.2.x before 1.2.4, and 1.3.x before 1.3.1 allows a sandbox bypass. Flatpak versions since 0.8.1 address CVE-2017-5226 by using a seccomp filter to prevent sandboxed apps from using the TIOCSTI ioctl, which could otherwise be used to inject commands into the controlling terminal so that they would be executed outside the sandbox after the sandboxed app exits. This fix was incomplete: on 64-bit platforms, the seccomp filter could be bypassed by an ioctl request number that has TIOCSTI in its 32 least significant bits and an arbitrary nonzero value in its 32 most significant bits, which the Linux kernel would treat as equivalent to TIOCSTI.
Flatpak before 1.0.7, and 1.1.x and 1.2.x before 1.2.3, exposes /proc in the apply_extra script sandbox, which allows attackers to modify a host-side executable file.
In dbus-proxy/flatpak-proxy.c in Flatpak before 0.8.9, and 0.9.x and 0.10.x before 0.10.3, crafted D-Bus messages to the host can be used to break out of the sandbox, because whitespace handling in the proxy is not identical to whitespace handling in the daemon.
In Flatpak before 0.8.7, a third-party app repository could include malicious apps that contain files with inappropriate permissions, for example setuid or world-writable. The files are deployed with those permissions, which would let a local attacker run the setuid executable or write to the world-writable location. In the case of the "system helper" component, files deployed as part of the app are owned by root, so in the worst case they could be setuid root.