The exif_process_IFD_TAG function in ext/exif/exif.c in PHP before 5.5.35, 5.6.x before 5.6.21, and 7.x before 7.0.6 does not properly construct spprintf arguments, which allows remote attackers to cause a denial of service (out-of-bounds read) or possibly have unspecified other impact via crafted header data.