The MessageDigest.isEqual function in Java Runtime Environment (JRE) in Sun Java SE in JDK and JRE 5.0 before Update 22 JDK and JRE 6 before Update 17 SDK and JRE 1.3.x before 1.3.1_27 and SDK and JRE 1.4.x before 1.4.2_24 allows remote attackers to spoof HMAC-based digital signatures and possibly bypass authentication via unspecified vectors related to \timing attack vulnerabilities \ aka Bug Id 6863503.