The ClamAV AntiVirus software versions 0.99.2 and prior contain a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to a lack of input validation checking mechanisms during certain mail parsing operations (mbox.c operations on bounce messages). If successfully exploited, the ClamAV software could allow a variable pointing to the mail body which could cause a used after being free (use-after-free) instance which may lead to a disruption of services on an affected device to include a denial of service condition.
https://usn.ubuntu.com/3550-2/
https://usn.ubuntu.com/3550-1/
https://lists.debian.org/debian-lts-announce/2018/01/msg00035.html
http://blog.clamav.net/2018/01/clamav-0993-has-been-released.html