The pop_msg function in qpopper 4.0.x before 4.0.5fc2 does not null terminate a message buffer after a call to Qvsnprintf, which could allow authenticated users to execute arbitrary code via a buffer overflow in a mdef command with a long macro name.
https://exchange.xforce.ibmcloud.com/vulnerabilities/11516
http://www.novell.com/linux/security/advisories/2003_018_qpopper.html
http://www.debian.org/security/2003/dsa-259
http://marc.info/?l=bugtraq&m=104792541215354&w=2
http://marc.info/?l=bugtraq&m=104768137314397&w=2