In Eclipse Mosquitto 1.5.0 to 1.6.5 inclusive, if a malicious MQTT client sends a SUBSCRIBE packet containing a topic that consists of approximately 65400 or more '/' characters, i.e. the topic hierarchy separator, then a stack overflow will occur.
https://www.debian.org/security/2019/dsa-4570
https://usn.ubuntu.com/4137-1/
https://seclists.org/bugtraq/2019/Nov/25
https://lists.debian.org/debian-lts-announce/2019/10/msg00035.html
https://bugs.eclipse.org/bugs/show_bug.cgi?id=551160
http://lists.opensuse.org/opensuse-security-announce/2019-10/msg00008.html
http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00077.html