libsafe 2.0-11 and earlier allows attackers to bypass protection against format string vulnerabilities via format strings that use the "'" and "I" characters, which are implemented in libc but not libsafe.
http://www.securityfocus.com/bid/4326
http://www.linux-mandrake.com/en/security/2002/MDKSA-2002-026.php
http://www.iss.net/security_center/static/8593.php
http://archives.neohapsis.com/archives/vulnwatch/2002-q1/0070.html