The JsonToBinaryStream() function is part of the protocol buffers C++ implementation and is used to parse JSON from a stream. If the input is broken up into separate chunks in a certain way, the parser will attempt to read bytes from a chunk that has already been freed.
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.