CVE-2025-58369: Typelevel FS2

Medium severity, CVSS 5.3. EPSS: 0.4% chance of exploitation in the next 30 days.

fs2 is a compositional, streaming I/O library for Scala. Versions up to and including 2.5.12, 3.0.0-M1 through 3.12.2, and 3.13.0-M1 through 3.13.0-M6 are vulnerable to denial of service attacks though TLS sessions using fs2-io on the JVM using the fs2.io.net.tls package. When establishing a TLS session, if one side of the connection shuts down `write` while the peer side is awaiting more data to progress the TLS handshake, the peer side will spin loop on the socket read, fully utilizing a CPU. The CPU is consumed until the overall connection is closed, potentially shutting down a fs2-io powered server. This issue is fixed in versions 2.5.13, 3.12.1, and 3.13.0-M7.

Affected products

• Typelevel FS2: from 3.0.0-M1, before 3.12.2 (fixed in 3.12.2); from 3.13.0-M1, before 3.13.0-M7 (fixed in 3.13.0-M7); before 2.5.13 (fixed in 2.5.13)

Published 2025-09-05. Last modified 2026-10-01.