It was discovered that xscreensaver did not correctly validate the return values from network authentication systems such as LDAP or NIS. A local attacker could bypass a locked screen if they were able to interrupt network connectivity.
The problem can be corrected by updating your system to the following package versions:
12 June 2007
A security issue affects these releases of Ubuntu and its derivatives:
It was discovered that xscreensaver did not correctly validate the return values from network authentication systems such as LDAP or NIS. A local attacker could bypass a locked screen if they were able to interrupt network connectivity.
The problem can be corrected by updating your system to the following package versions:
To update your system, please follow these instructions: https://wiki.ubuntu.com/Security/Upgrades.
After a standard system upgrade you need to restart your session to effect the necessary changes.
Vulmon