If a message consumer expects data of type "list of pointers", and if the consumer performs certain specific actions on such data, then a message producer can cause the consumer to read out-of-bounds memory. This could trigger a process crash in the consumer, or in some cases could allow exfiltration of private in-memory data.

The C++ Cap'n Proto library is also affected by this bug. See the advisory on the main Cap'n Proto repo for a succinct description of the exact circumstances in which the problem can arise.