source: http://www.securityfocus.com/bid/30690/info

Yelp is prone to a remote format-string vulnerability because the application fails to properly sanitize user-supplied input before including it in the format-specifier argument of a formatted-printing function.

A remote attacker may exploit this issue to execute arbitrary code with the privileges of the user running the affected application. Failed exploit attempts may cause denial-of-service conditions.

Yelp 2.23.1 is vulnerable; other versions may also be affected. 

ftp://%08x.%08x.%08x.%08x.%08x.%08x
%x%x%x%x%x%x://
%08x%08x 