Use-after-free in the RTMP protocol implementation in Apache bRPC (version < 1.18.0) on all platforms allows a malicious RTMP peer to crash

Use-after-free in the RTMP protocol implementation in Apache bRPC (version < 1.18.0) on all platforms allows a malicious RTMP peer to crash the process or potentially corrupt memory via a crafted Abort message.

Root Cause:
When processing an RTMP Abort (protocol control message type 2), the RTMP policy implementation deleted the target RtmpChunkStream object. The send path (RtmpUnsentMessage::AppendAndDestroySelf -> RtmpChunkStream::SerializeMessage) runs concurrently on sender threads and dereferences the same RtmpChunkStream object without synchronization. If a remote peer sends an Abort message naming a chunk stream that is concurrently being used to serialize an outgoing message, the stream object is freed while still in use, resulting in a use-after-free. Additionally, deleting the chunk stream discarded its previous message header, so subsequent compressed (type-3) chunk headers on that stream could no longer be decoded.

Affected Scenarios:
Any application using the bRPC RTMP protocol implementation (rtmp policy), either as an RTMP server or as an RTMP client, where the remote endpoint is untrusted. The attacker needs to send an Abort message targeting a chunk stream id that is concurrently used for sending, which can crash the process or lead to memory corruption.

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/3515