Details for this vulnerability have not been published by NIST at this point. Descriptions from software vendor advisories for this issue are provided below.
USN-4593-1 fixed a vulnerability in FreeType. This update provides the corresponding update for Ubuntu 14.04 ESM.
Original advisory details:
Sergei Glazunov discovered that FreeType did not correctly handle certain malformed font files. If a user were tricked into using a specially crafted font file, a remote attacker could cause FreeType to crash or possibly execute arbitrary code with user privileges.