Uncontrolled Resource Consumption

Summary

Netty's HTTP/3 codec versions from 4.2.0.Final through 4.2.17.Final contain a Denial-of-Service (DoS) vulnerability in the QPACK prefixed-integer decoder "QpackUtil.decodePrefixedInteger", which does not bound the number of continuation bytes it will process. A remote, unauthenticated peer can open a QPACK unidirectional stream (type 0x02 encoder or 0x03 decoder) and send a first byte with all prefix bits set (e.g. 0xFF for a 7-bit prefix or 0x3F for a 5-bit prefix) followed by an endless run of 0x80 continuation bytes. The decoder returns -1 ('need more bytes'), so callers never consume the input, the "ByteToMessageDecoder cumulator" grows without bound, and each "decode()" invocation re-scans the whole accumulated buffer, yielding O(N^2) CPU cost. The result is unbounded per-connection heap growth "OutOfMemoryError" and event-loop CPU starvation, reachable in every configuration.