CVE-2025-61778
Akka.Remote TLS did not properly implement certificate-based authentication
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
Akka.Remote.NETAkka.ClusterReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Akka.Remote | ≥ 1.2.0&&< 1.5.52 | 1.5.52 |
| .NETNuGet | Akka.Cluster | ≥ 1.2.0&&< 1.5.52 | 1.5.52 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Akka.Remote. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update Akka.Remote to 1.5.52 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-61778 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2025-61778 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2025-61778. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2025-61778 in your dependencies?
O3 detects CVE-2025-61778 across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.