A vulnerability in xdg-dbus-proxy before version 0.1.2-3.oe2403sp1 allows attackers to bypass message filtering on the D-Bus session bus by setting a reply serial number on non-reply messages. This flaw can be exploited by a malicious or compromised Flatpak application to execute arbitrary code outside its sandbox. xdg-dbus-proxy is used as part of the sandbox boundary for Flatpak and other app frameworks like Firejail. The issue is fixed in version 0.1.2-3.oe2403sp1.