A new vulnerability was discovered in Netscape this week.  Netscape incorrectly handles GIF files, that could lead to a buffer overflow which is remotely exploitable through a specially generated GIF file.

http://secunia.com/advisories/15103/

Secunia Advisory: SA15103   
Release Date: 2005-04-26
Critical: Highly critical
Impact: System access
Where: From remote
Solution Status: Unpatched
Software: Netscape 6.x   Netscape 7.x