Apache bRPC: NULL Pointer Dereference in RTMP createStream Error Path Leading to Remote Denial of Service

NULL pointer dereference in the RTMP protocol implementation in Apache bRPC (version < 1.18.0) on all platforms allows remote attackers to crash the server (denial of service) via a crafted createStream command.

Root Cause:
When an RTMP service rejects a createStream request by returning a null stream from RtmpService::NewStream(), the server sends an error response to the client. If writing this rejection response fails (for example, because the client closes the connection immediately after sending the createStream command), the error-handling path in RtmpChunkStream::OnCreateStream() dereferences the null stream pointer to access stream->_onfail_id, causing the process to crash.

Affected Scenarios:
Run an Apache bRPC RTMP server whose RtmpService::NewStream() may return null (i.e., the service rejects createStream requests). A remote client that sends a createStream command and then closes the connection before the rejection response is written can crash the server.

How to Fix:
(Choose one of the following options)

1. Upgrade bRPC to version 1.18.0, which fixes this issue.
2. Apply this patch: https://github.com/apache/brpc/pull/3508