The TtfUtil:LocaLookup function in TtfUtil.cpp in Libgraphite in Graphite 2 1.2.4, as used in Mozilla Firefox before 43.0 and Firefox ESR 38.x before 38.6.1, incorrectly validates a size value, which allows remote attackers to obtain sensitive information or cause a denial of service (out-of-bounds read and application crash) via a crafted Graphite smart font.