USN-4134-1 fixed a vulnerability in IBus. The security fix introduced a regression when being used with Qt applications. This update reverts the security fix pending further investigation.
Original advisory details:
Simon McVittie discovered that IBus did not enforce appropriate access controls on its private D-Bus socket. A local unprivileged user who discovers the IBus socket address of another user could exploit this to capture the key strokes of the other user.