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.

Java Runtime Environment (JRE) Bytecode Verifier allows remote attackers to escape the Java sandbox and execute commands via an applet containing an illegal cast operation, as seen in (1) Microsoft VM build 3802 and earlier as used in Internet Explorer 4.x and 5.x, (2) Netscape 6.2.1 and earlier, and possibly other implementations that use vulnerable versions of SDK or JDK, aka a variant of the "Virtual Machine Verifier" vulnerability.

Java Runtime Environment (JRE) and SDK 1.2 through 1.3.0_04 allows untrusted applets to access the system clipboard.