ZoIPer 2.22, and possibly other versions before 2.24 Library 5324, allows remote attackers to cause a denial of service (crash) via a SIP INVITE request with an empty Call-Info header.
https://exchange.xforce.ibmcloud.com/vulnerabilities/53792
https://euvd.enisa.europa.eu/vulnerability/EUVD-2009-3677
http://secunia.com/advisories/37015
http://packetstormsecurity.org/0910-exploits/zoiper_dos.py.txt