fs2: Half-shutdown of socket during TLS handshake may result in spin loop on opposite side

Summary

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.

Timeline

1. Sep 5, 2025, 9:59 PM UTCCVE published
2. Sep 8, 2025, 8:09 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Nov 7, 2025, 11:52 AM UTCRecord last updated

Affected versions

• typelevel fs2

  From 3.0.0-M1 · fixed in 3.12.2; From 3.13.0-M1 · fixed in 3.13.0-M7; fixed in 2.5.13

• co.fs2:fs2-io_2.12Maven

  From 3.0.0-M1 · fixed in 3.12.2

• co.fs2:fs2-io_2.12Maven

  From 3.13.0-M1 · fixed in 3.13.0-M7

• co.fs2:fs2-io_2.13Maven

  From 3.0.0-M1 · fixed in 3.12.2

• co.fs2:fs2-io_2.13Maven

  From 3.13.0-M1 · fixed in 3.13.0-M7

• co.fs2:fs2-io_3Maven

  From 3.0.0-M1 · fixed in 3.12.2

• co.fs2:fs2-io_3Maven

  From 3.13.0-M1 · fixed in 3.13.0-M7

• co.fs2:fs2-io_0.26Maven

  All versions

• co.fs2:fs2-io_0.27Maven

  All versions

• co.fs2:fs2-io_2.11Maven

  All versions

• co.fs2:fs2-io_2.12.0-M4Maven

  All versions

• co.fs2:fs2-io_2.12.0-RC1Maven

  All versions

• co.fs2:fs2-io_2.12.0-M5Maven

  All versions

• co.fs2:fs2-io_2.12.0-RC2Maven

  All versions

• co.fs2:fs2-io_2.13.0-M5Maven

  All versions

• co.fs2:fs2-io_2.12Maven

  fixed in 2.5.13

• co.fs2:fs2-io_2.13Maven

  fixed in 2.5.13

• co.fs2:fs2-io_3Maven

  fixed in 2.5.13

References 7