The SIMPLE protocol functionality in Pidgin before 2.10.8 allows remote attackers to have an unspecified impact via a negative Content-Length header, which triggers a buffer overflow.
https://rhn.redhat.com/errata/RHSA-2014-0139.html
http://www.ubuntu.com/usn/USN-2100-1
http://www.securityfocus.com/bid/65195
http://www.pidgin.im/news/security/?id=84