typelevel fs2 up to 3.12.1/3.13.0-M6 TLS Handshake resource consumption

Summaryinfo

A vulnerability was found in typelevel fs2 up to 3.12.1/3.13.0-M6. It has been declared as problematic. Affected by this issue is some unknown functionality of the component TLS Handshake Handler. Executing a manipulation can lead to resource consumption. This vulnerability is tracked as CVE-2025-58369. The attack can be launched remotely. No exploit exists. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in typelevel fs2 up to 3.12.1/3.13.0-M6. It has been declared as problematic. This vulnerability affects some unknown processing of the component TLS Handshake Handler. The manipulation with an unknown input leads to a resource consumption vulnerability. The CWE definition for the vulnerability is CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. As an impact it is known to affect availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2025-58369 since 08/29/2025. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 3.12.2 or 3.13.0-M7 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch 46e2dc3abf994dcf3d0b804b2ddb3c10c04d4976 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2025-27048). Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• typelevel

Name

• fs2

Version

• 3.12.0
• 3.12.1
• 3.13.0-M6

License

• open-source

Website

• Product: https://github.com/typelevel/fs2/

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Once again VulDB remains the best source for vulnerability data.

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