CVE-2026-59279: Unbounded persistent session allocation via repeated initialize requests

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-21 · updated 2026-10-16
Weakness: CWE-770

Description

The MCP Streamable HTTP server transport (WebFlux and WebMvc variants) does not place any limit on the number of sessions it retains, and by default does not require clients to be authenticated. As a result, a remote attacker can cause the server to accumulate an unbounded number of sessions over time, gradually exhausting available memory and ultimately causing a Denial of Service that affects all legitimate clients. Affected versions: Spring AI: 2.0.0

Affected products

Spring AI: from 2.0.0 before 2.0.1 — fixed in 2.0.1
Spring AI: 2.0.0

How to fix

Upgrade to a fixed version: Spring AI 2.0.1. Check the vendor advisory for mitigations.

References

https://spring.io/security/cve-2026-59279

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