CVE-2026-94422xdg-dbus-proxy: message filtering bypass via reply serial allows sandbox escape

Description

An incorrect implementation of message filtering in xdg-dbus-proxy versions before 0.1.9 allows an attacker to bypass the intended message filtering on the D-Bus session bus by setting a reply serial number on non-reply messages. A malicious or compromised Flatpak app could use this to achieve arbitrary code execution outside its sandbox. xdg-dbus-proxy was designed to be part of the sandbox boundary for Flatpak, but it is released as a separate project and is sometimes used by other app frameworks such as Firejail.

Data: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Published as the sources state it, in English.

Affected products and versions

References and patches

• https://access.redhat.com/security/cve/CVE-2026-94422 vendor-advisory
• https://github.com/flatpak/xdg-dbus-proxy/security/advisories/GHSA-2cgv-pwcq-wvpq third-party-advisory
• https://github.com/flatpak/xdg-dbus-proxy/commit/e5702fca4dba9600721921fbca2dbc39dc5ca400 patch
• https://github.com/flatpak/xdg-dbus-proxy/commit/fc027f759316fb2a6c45648200b6f100202eb84e patch
• https://github.com/flatpak/xdg-dbus-proxy/commit/e4465a0dfe96da3b39929a30a1ac3a22b16223e3 patch
• https://bugzilla.redhat.com/show_bug.cgi?id=2542235 issue-tracking
• http://www.openwall.com/lists/oss-security/2026/09/23/5
• https://lists.debian.org/debian-lts-announce/2026/10/msg00050.html