When parsing code receives a payload for a variable length field where the length is specified in the code as some arbitrarily large number (assume INT32_MAX for example) this will immediately try to allocate an ArrayList to hold this many elements, before checking whether this is a reasonable array size given the available data.
The fix for this is to instead throw a runtime exception if the length of a variably sized container exceeds the amount of remaining data. Then, the worst a user can do is force the server to allocate 8x the size of the actual delivered data (if they claim there are N elements for a container of Objects (i.e. not a byte string) and each Object bottoms out in an 8 byte pointer in the ArrayList's backing array).
This was identified by fuzzing the kafka request parsing code.