Coraza before 3.8.1 extracts multipart upload filenames with Go's mime.ParseMediaType, which silently ignores RFC 5987 filename parameters whose charset is not utf-8 or us-ascii. Unauthenticated attackers can send a decoy filename with filename=iso-8859-1''shell.php, or filename alone, so FILES-based rules never see the real name, letting dangerous uploads reach backends that honor filename.