Insufficient boundary checks when processing M_SOFx markers from JPEG headers in the GD extension could allow access to out-of-bounds memory via a maliciously constructed invalid JPEG input. This issue affects HHVM versions prior to 3.30.9, all versions between 4.0.0 and 4.8.3, all versions between 4.9.0 and 4.15.2, and versions 4.16.0 to 4.16.3, 4.17.0 to 4.17.2, 4.18.0 to 4.18.1, 4.19.0, 4.20.0 to 4.20.1.