The Data function in class.smtp.php in PHPMailer 1.7.2 and earlier allows remote attackers to cause a denial of service (infinite loop leading to memory and CPU consumption) via a long header field.
seclists.org/lists/bugtraq/2005/May/0337.html
secunia.com/advisories/15543
secunia.com/advisories/18732
secunia.com/advisories/25726
securitytracker.com/id?1014069
sourceforge.net/project/shownotes.php?release_id=341210&group_id=26031
www.cybsec.com/vuln/PHPMailer-DOS.pdf
www.securityfocus.com/bid/13805
www.vupen.com/english/advisories/2006/0448
www.vupen.com/english/advisories/2007/2242