CVE 2008-2829
php_imap.c in PHP 5.2.5, 5.2.6, 4.x, and other versions, uses obsolete API calls that allow context-dependent attackers to cause a denial of service (crash) and possibly execute arbitrary code via a long IMAP request, which triggers an "rfc822.c legacy routine buffer overflow" error message, related to the rfc822_
See the 
CVE page on Mitre.org
for more details.
