USN-83-1 fixed some vulnerabilities in the “lesstif2” library. The older “lesstif1” library was also affected, however, a fix was not yet available at that time. This USN fixes the flaws for lesstif1.
Please note that there are no supported applications that use this library, so this only affects you if you use third-party applications which use lesstif1.
For your convenience, here is the relevant part of the USN-83-1 description:
Several vulnerabilities have been found in the XPM image decoding functions of the LessTif library. If an attacker tricked a user into loading a malicious XPM image with an application that uses LessTif, he could exploit this to execute arbitrary code in the context of the user opening the image.
Ubuntu does not contain any server applications using LessTif, so there is no possibility of privilege escalation.