The mconvert function in softmagic.c in file before 5.21, as used in the Fileinfo component in PHP before 5.4.37, 5.5.x before 5.5.21, and 5.6.x before 5.6.5, does not properly handle a certain string-length field during a copy of a truncated version of a Pascal string, which might allow remote attackers to cause a denial of service (out-of-bounds memory access and application crash) via a crafted file.