commands.c in qmail, when running on 64 bit platforms with a large amount of virtual memory, allows remote attackers to cause a denial of service and possibly execute arbitrary code via a long SMTP command without a space character, which causes an array to be referenced with a negative index.
https://www.debian.org/security/2020/dsa-4692
https://usn.ubuntu.com/4556-1/
https://security.gentoo.org/glsa/202007-01
https://lists.debian.org/debian-lts-announce/2020/06/msg00002.html
http://www.openwall.com/lists/oss-security/2020/05/20/2
http://www.openwall.com/lists/oss-security/2020/05/19/8
http://securitytracker.com/id?1013911
http://seclists.org/fulldisclosure/2020/May/42
http://archives.neohapsis.com/archives/fulldisclosure/2005-05/0101.html