The Sun Java Plugin capability in Java 2 Runtime Environment (JRE) 1.4.2_01, 1.4.2_04, and possibly earlier versions, does not properly restrict access between Javascript and Java applets during data transfer, which allows remote attackers to load unsafe classes and execute arbitrary code by using the reflection API to access private Java packages.

readObject in (1) Java Runtime Environment (JRE) and (2) Software Development Kit (SDK) 1.4.0 through 1.4.2_05 allows remote attackers to cause a denial of service (JVM unresponsive) via crafted serialized data.