Advisory [CVE-2026-78334] Missing authentication in the streaming RPC path of Apache bRPC (version < 1.18.0) on all platforms allows a remote attacker to bypass server authentication and inject or deliver streaming frames, when a server is configured with an Authenticator

Missing authentication in the streaming RPC path of Apache bRPC (version < 1.18.0) on all platforms allows a remote attacker to bypass server authentication and inject or deliver streaming frames, when a server is configured with an Authenticator.

Root Cause: When authentication is configured, streaming RPC frames are consumed directly by the streaming parser (ParseStreamingMessage) and never pass through InputMessenger's authentication hook, so an unauthenticated peer can exchange frames without being authenticated.

In addition, a server-accepted stream is bound lazily to the first frame that happens to carry its id, so a stream could accept a frame carrying its id from a socket other than the socket that created the stream.

Affected Scenarios: A bRPC server configured with authentication that serves streaming RPC from an untrusted network, or a deployment where a foreign connection can impersonate a stream by id, can be made to accept unauthorized streaming frames.

How to Fix: Upgrade bRPC to 1.18.0, which fixes this issue, or apply the patch in PR.

Note: The fix rejects streaming frames on server sockets when configured authentication has not completed, and keeps server-accepted streams bound to the socket of their creating RPC and rejects frames arriving from another socket.