CVE-2026-67431: MCP Ruby SDK: Ruby SSE Session Poisoning
Vulnerability: Missing Session Ownership Validation in the Ruby MCP SDK’s Streamable and SSE HTTP transport implementation. Any attacker with a stolen session ID can execute tools with the victim’s session. This is a silent attack - the victim’s session is compromised and being used for unauthorized actions, but it is hard to know for the victim
References
- github.com/advisories/GHSA-5p9g-j988-pcwv
- github.com/modelcontextprotocol/ruby-sdk/commit/35466605319a34e4c7808712ae9bb1ca1afb2356
- github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0
- github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-5p9g-j988-pcwv
- nvd.nist.gov/vuln/detail/CVE-2026-67431
Code Behaviors & Features
Detect and mitigate CVE-2026-67431 with GitLab Dependency Scanning
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