CVE-2025-61778: Akka.Remote TLS did not properly implement certificate-based authentication

This is a critical network security vulnerability for Akka.Remote users who have SSL / TLS enabled on their Akka.Remote connections and were expecting certificate-based authentication to be enforced on all peers attempting to join the network.

In all versions of Akka.Remote from v1.2.0 to v1.5.51, TLS could be enabled via our akka.remote.dot-netty.tcp transport and this would correctly enforce private key validation on the server-side of inbound connections. Akka.Remote, however, never asked the outbound-connecting client to present ITS certificate - therefore it’s possible for untrusted parties to connect to a private key’d Akka.NET cluster and begin communicating with it without any certificate.

The issue here is that for certificate-based authentication to work properly, ensuring that all members of the Akka.Remote network are secured with the same private key, Akka.Remote needed to implement mutual TLS. This was not the case before Akka.NET v1.5.52.

If you are running Akka.NET inside a private network you fully control or you were never using TLS in the first place, then this bug has no impact on you. However: if you are using TLS to secure your network YOU MUST upgrade to Akka.NET V1.5.52 or later.