{"id":"CVE-2026-59951","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-59951","generatedAt":"2026-10-28T02:23:50.935Z","title":"The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP).","description":"The MCP Python SDK, called mcp on PyPI, is a Python implementation of the Model Context Protocol (MCP). From 1.8.0 until 1.30.0 and 2.2.0, stateful Streamable HTTP servers, including FastMCP, MCPServer, Server.streamable_http_app(), and StreamableHTTPSessionManager, retain session entries without an idle expiration or aggregate session-count limit. DELETE, refused opening requests, and completed sessions do not reliably discard their entries, and each entry can retain parsed initialize parameters. A client that can reach the endpoint can therefore create ordinary short requests that grow server memory without bound until restart. Stateless HTTP, stdio, and SSE transports are not affected. This issue is fixed in versions 1.30.0 and 2.2.0.","published":"2026-10-14T17:18:30.000Z","lastModified":"2026-10-16T16:00:34.000Z","status":"Awaiting Analysis","sourceIdentifier":"security-advisories@github.com","cvss":{"version":"4.0","score":6.9,"severity":"MEDIUM","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M"},"cwe":["CWE-400","CWE-772"],"affected":[],"epss":{"score":0.00458,"percentile":0.39466,"date":"2026-10-26","history":[{"date":"2026-10-15","score":0.00458,"percentile":0.38172}]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"low","text":"Lower severity and a low EPSS score (0.46%). Track it; it rarely justifies an emergency change on its own."},"changes":[{"kind":"new","label":"New CVE","at":"2026-10-14T17:18:30.000Z","detail":{"score":"6.9","severity":"MEDIUM","publishedAt":"2026-10-14T17:18:29.690Z"},"summary":"New CVE, medium severity (CVSS 6.9)."}],"references":[{"url":"https://github.com/modelcontextprotocol/python-sdk/commit/92120b4b0f50385af096592d7cee932fc1d994e7","source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/python-sdk/commit/d2290ca3434731b68ea3e2270bc06a6e6575931b","source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/python-sdk/pull/3395","source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/python-sdk/pull/3426","source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/python-sdk/releases/tag/v1.30.0","source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/python-sdk/releases/tag/v2.2.0","source":"security-advisories@github.com"},{"url":"https://github.com/modelcontextprotocol/python-sdk/security/advisories/GHSA-84m7-p3x7-pcfv","source":"security-advisories@github.com"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-59951","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}