It was discovered that LibASS incorrectly handled certain ASS files. A remote attacker could possibly use this issue to cause a denial of service. One of the issues, CVE-2016-7970, only affected Ubuntu 16.04 ESM. (CVE-2016-7969, CVE-2016-7970, CVE-2016-7972)
It was discovered that LibASS incorrectly handled parsing operations for specific nested character strings. An attacker could possibly use this issue to cause a denial of service. This issue was only fixed in Ubuntu 16.04 LTS. (CVE-2020-24994)