An agent which tries to redefine a class with an incomplete classfile can cause a VM crash during classfile parsing. Refer to the details of CR 6545149. In that case, the agent is not reading the full classfile and passing the partial classfile to the VM, which is crashing.
The class file parser silently ignores a number of legitimate errors for trusted classes (those loaded by bootstrap and not going to be verified). Those classes should not be given a free pass since if the data is wrong it can crash the VM.
Added a single check to make sure the method signature is valid before trying to parse it. This check now occurs regardless of the verification state of the class.