CVE-2026-67431

HIGH8.3

MCP Ruby SDK: Ruby SSE Session Poisoning

Published Jul 29, 2026

Modified 3 weeks ago

Details

MCP Ruby SDK is the official Ruby SDK for Model Context Protocol servers and clients. Prior to 0.23.0, MCP::Server::Transports::StreamableHTTPTransport in the mcp gem does not bind a session ID to a session owner, allowing an attacker with a stolen session ID to send tools/call requests that execute in the victim's session. This issue is fixed in version 0.23.0.

References

WEB

https://github.com/modelcontextprotocol/ruby-sdk/commit/35466605319a34e4c7808712ae9bb1ca1afb2356

WEB

https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0

WEB

https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-5p9g-j988-pcwv

ADVISORY

https://www.cve.org/CVERecord?id=CVE-2026-67431

CVSS Analysis

CVSS v4.0

8.3