Description
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.
References7
- github.com/typelevel/fs2/commit/46e2dc3abf994dcf3d0b804b2ddb3c1…
- github.com/typelevel/fs2/commit/5c6c4c6c1ef330f7e6b53661ecc63d5…
- github.com/typelevel/fs2/commit/edf0c4f2e660360d1c1a8c5377ce322…
- github.com/typelevel/fs2/issues/3590
- github.com/typelevel/fs2/releases/tag/v3.12.2
- github.com/typelevel/fs2/releases/tag/v3.13.0-M7
- github.com/typelevel/fs2/security/advisories/GHSA-rrw2-px9j-qffj
Metrics
- CVSS 3.1
-
5.3
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L - EPSS — exploit probability
- 0% percentile: 41 · as of 8 November 2026
- CWE
- CWE-400
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.