A vulnerability in c-client library versions 2000, 2001, and 2004 allows mail_open to be used as a vector to open a stream to local files, bypassing safemode and open_basedir restrictions.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/44290/cclientBypass.txt
Source: https://packetstormsecurity.com/files/44290/cclientBypass.txt.html