Apache bRPC: Remote denial of service (crash) via malformed stream feedback frames

Enforceable assertion in the streaming feature of Apache bRPC (version < 1.18.0) on all platforms allows a remote attacker to crash the server process by sending a malformed stream feedback frame.

Root Cause: When handling FRAME_TYPE_FEEDBACK frames, bRPC calls Stream::SetRemoteConsumed() which contains CHECK(_cur_buf_size > 0) and unconditionally asserts CHECK(buf.IsEmpty()) on the frame payload. A feedback frame that carries an unexpected payload, or a feedback frame received on a stream where flow control is disabled (cur_buf_size == 0), reaches these assertions. On failure, CHECK failures abort the process, allowing an unauthenticated single client (once a stream is established) to terminate the server and cause a denial of service.

Affected Scenarios: Use bRPC server with the streaming control feature (Stream API) served from untrusted network.

How to Fix:

1. Upgrade bRPC to version 1.18.0, which fixes this issue.
2. Apply this patch: https://github.com/apache/brpc/pull/3494

The fix rejects malformed feedback frames with EPROTO and closes only the affected stream instead of crashing the whole process, and it bounds buffer shrinking so cur_buf_size never drops to 0 while flow control is enabled.