USN-5438-1 fixed a vulnerability in HTMLDOC. This update provides the corresponding update for Ubuntu 14.04 ESM and Ubuntu 16.04 ESM.
Original advisory details:
It was discovered that HTMLDOC did not properly manage memory under certain circumstances. If a user were tricked into opening a specially crafted HTML file, a remote attacker could possibly use this issue to cause HTMLDOC to crash, resulting in a denial of service, or possibly execute arbitrary code.