It was discovered that unplugging one of the monitors in a
multi-monitor
setup can cause xscreensaver to crash. Someone with
physical access to
a machine could use this problem to bypass a locked session.
For the oldstable distribution (wheezy), this problem has
been fixed
in version 5.15-3+deb7u1.
For the stable distribution (jessie), this problem has been
fixed in
version 5.30-1+deb8u1.
For the testing (stretch) and unstable (sid) distributions,
this problem
has been fixed in version 5.34-1.
We recommend that you upgrade your xscreensaver packages.
Further information about Debian Security Advisories, how to
apply
these updates to your system and frequently asked questions
can be
found at: https://www.debian.org/security/