CVE-2025-61778
CriticalCVSS 9.3Exploitation Probability (EPSS)
Low risk22th percentile - higher than 22% of all known CVEs
Summary
The vulnerability in Akka.Remote (versions 1.2.0 to 1.5.51) is the lack of mutual TLS (mTLS) — the outbound-connecting client is not required to present its certificate, allowing untrusted parties to join an Akka.NET cluster even when TLS is enabled. The issue is fixed in version 1.5.52, which enforces mTLS by default and introduces fail-fast semantics for missing or invalid private keys.
Risk Assessment
The risk is that an external attacker can connect to a TLS-protected Akka.NET cluster without a valid certificate, potentially leading to unauthorized access or disruption. Organizations using TLS to secure their networks are particularly exposed until they upgrade to 1.5.52.
Recommendation
Upgrade Akka.NET to version 1.5.52 or later immediately to enforce mTLS and mitigate the risk. If upgrading is not possible, avoid exposing the application publicly.
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Original NVD description (English source)
Akka.NET is a .NET port of the Akka project from the Scala / Java community. 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. Those who run Akka.NET inside a private network that they fully control or who were never using TLS in the first place are now affected by the bug. However, those who use TLS to secure their networks must upgrade to Akka.NET V1.5.52 or later. One patch forces "fail fast" semantics if TLS is enabled but the private key is missing or invalid. Previous versions would only check that once connection attempts occurred. The second patch, a critical fix, enforces mutual TLS (mTLS) by default, so both parties must be keyed using the same certificate. As a workaround, avoid exposing the application publicly to avoid the vulnerability having a practical impact on one's application. However, upgrading to version 1.5.52 is still recommended by the maintainers.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

