The php_if_imap_mime_header_decode function in the IMAP functionality in PHP before 4.2.2 allows remote attackers to cause a denial of service (crash) via an e-mail header with a long "To" header.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2002-2193
https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=175040
http://www.redhat.com/support/errata/RHSA-2006-0567.html