Denial of Service Vulnerability in fs2 Streaming I/O Library for Scala

CVE-2025-58369

What is CVE-2025-58369?

The fs2 library, utilized for compositional and streaming I/O in Scala applications, is susceptible to a denial of service attack during TLS session establishment. When one side of the connection terminates its write operations prematurely while the peer waits for further data to complete the TLS handshake, the peer may enter a spin loop on socket read operations. This continuous CPU usage can lead to severe performance degradation, potentially incapacitating servers reliant on the fs2-io framework. The issue has been resolved in fs2 versions 3.12.1 and 3.13.0-M7.

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