CVE-2025-58369 is a medium severity vulnerability affecting the typelevel fs2 library, a compositional streaming I/O library for Scala, specifically versions prior to 3.12.2 and between 3.13.0-M1 and 3.13.0-M6. The vulnerability arises in the TLS session establishment process when using the fs2-io module on the JVM, particularly within the fs2.io.net.tls package. During a TLS handshake, if one side of the connection shuts down its write stream while the peer side is still awaiting data to progress the handshake, the peer side enters a spin loop on the socket read operation. This results in uncontrolled CPU consumption, effectively a denial of service (DoS) condition, as the CPU remains fully utilized until the connection is closed. This can lead to resource exhaustion on servers that rely on fs2-io for TLS connections, potentially causing service degradation or outages. The root cause is an uncontrolled resource consumption issue classified under CWE-400. The vulnerability does not impact confidentiality or integrity but affects availability by exhausting CPU resources. The issue has been addressed in fs2 versions 3.12.1 and 3.13.0-M7 and later. No known exploits are reported in the wild as of the publication date, and the CVSS v3.1 base score is 5.3, reflecting a medium severity level due to network attack vector, low attack complexity, no privileges or user interaction required, and impact limited to availability.

For European organizations, the impact of CVE-2025-58369 primarily concerns availability disruptions in services that utilize the fs2 library for streaming I/O over TLS on JVM platforms. Organizations running Scala-based applications or microservices that depend on fs2-io for secure communications may experience high CPU utilization leading to denial of service conditions, potentially causing application downtime or degraded performance. This can affect financial institutions, government services, and enterprises relying on real-time data streaming or secure communications. The vulnerability could be exploited remotely without authentication or user interaction, increasing the risk of automated or large-scale DoS attacks. While the vulnerability does not compromise data confidentiality or integrity, the availability impact could disrupt critical business operations, especially in sectors with stringent uptime requirements. European organizations with limited monitoring of JVM-based TLS connections or those slow to update dependencies may be particularly vulnerable to service interruptions.

To mitigate this vulnerability, European organizations should: 1) Immediately upgrade the fs2 library to version 3.12.1 or later, or 3.13.0-M7 or later, as these versions contain the fix for the TLS handshake spin loop issue. 2) Audit all Scala-based applications and services to identify usage of vulnerable fs2 versions, including transitive dependencies in build configurations (e.g., sbt, Maven). 3) Implement runtime monitoring of CPU utilization and network socket states on JVM hosts to detect abnormal resource consumption patterns indicative of this vulnerability being triggered. 4) Employ network-level rate limiting or connection throttling on TLS endpoints to reduce the risk of sustained DoS attempts exploiting this issue. 5) Consider deploying JVM-level TLS handshake timeouts or socket read timeouts as a temporary workaround to prevent indefinite spin loops. 6) Engage in regular dependency management and security scanning to promptly identify and remediate vulnerable library versions. 7) Coordinate with development teams to incorporate secure coding practices and TLS session management improvements to avoid similar resource exhaustion issues.