In Apache SpamAssassin before 3.4.3, a message can be crafted in a way to use excessive resources. Upgrading to SA 3.4.3 as soon as possible is the recommended fix but details will not be shared publicly.
{ "availability": "Available with Ubuntu Pro (Infra-only): https://ubuntu.com/pro", "ubuntu_priority": "medium", "binaries": [ { "spamassassin": "3.4.2-0ubuntu0.14.04.1+esm1", "spamc": "3.4.2-0ubuntu0.14.04.1+esm1", "sa-compile": "3.4.2-0ubuntu0.14.04.1+esm1", "spamc-dbgsym": "3.4.2-0ubuntu0.14.04.1+esm1" } ] }