{"id":"CVE-2026-67431","aliases":["GHSA-5p9g-j988-pcwv"],"url":"https://o3.security/vulnerability/CVE-2026-67431","summary":"MCP Ruby SDK: Ruby SSE Session Poisoning","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.","published":"2026-07-29T19:15:32.340Z","modified":"2026-08-12T03:51:12.865038282Z","cvss":null,"epss":{"score":0.00292,"percentile":0.21682,"asOf":"2026-09-13"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"RubyGems","name":"mcp","fixedVersion":"0.23.0"}],"fix":{"url":"https://github.com/modelcontextprotocol/ruby-sdk/commit/35466605319a34e4c7808712ae9bb1ca1afb2356","label":"modelcontextprotocol/ruby-sdk@3546660"},"references":[{"type":"WEB","url":"https://github.com/modelcontextprotocol/ruby-sdk/releases/tag/v0.23.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/67xxx/CVE-2026-67431.json"},{"type":"ADVISORY","url":"https://github.com/modelcontextprotocol/ruby-sdk/security/advisories/GHSA-5p9g-j988-pcwv"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-67431"},{"type":"FIX","url":"https://github.com/modelcontextprotocol/ruby-sdk/commit/35466605319a34e4c7808712ae9bb1ca1afb2356"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:12.865038282Z"}}