{"id":"CVE-2026-0621","aliases":["GHSA-8r9q-7v3j-jr4g"],"url":"https://o3.security/vulnerability/CVE-2026-0621","summary":"MCP TypeScript SDK UriTemplate Exploded Array Pattern ReDoS","details":"### Impact\n\nA ReDoS vulnerability in the `UriTemplate` class allows attackers to cause denial of service. The `partToRegExp()` function generates a regex pattern with nested quantifiers (`([^/]+(?:,[^/]+)*)`) for exploded template variables (e.g., `{/id*}`, `{?tags*}`), causing catastrophic backtracking on malicious input.\n\n**Who is affected:** MCP servers that register resource templates with exploded array patterns and accept requests from untrusted clients.\n\n**Attack result:** An attacker sends a crafted URI via `resources/read` request, causing 100% CPU utilization, server hang/crash, and denial of service for all clients.\n\n### Affected Versions\n\nAll versions of `@modelcontextprotocol/sdk` prior to the patched release.\n\n### Patches\n\nv1.25.2 contains b392f02ffcf37c088dbd114fedf25026ec3913d3 the fix modifies the regex pattern to prevent backtracking.\n\n### Workarounds\n\n- Avoid using exploded patterns (`{/id*}`, `{?tags*}`) in resource templates\n- Implement request timeouts and rate limiting\n- Validate URIs before processing to reject suspicious patterns","published":"2026-01-05T20:57:14.515Z","modified":"2026-10-28T02:30:55.258232743Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"@modelcontextprotocol/sdk","fixedVersion":"1.25.2"}],"fix":{"url":"https://github.com/modelcontextprotocol/typescript-sdk/commit/7f0cf730","label":"modelcontextprotocol/typescript-sdk@7f0cf73"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/0xxx/CVE-2026-0621.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-0621"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/mcp-typescript-sdk-uritemplate-exploded-array-pattern-redos"},{"type":"REPORT","url":"https://github.com/modelcontextprotocol/typescript-sdk/issues/965"},{"type":"PACKAGE","url":"https://github.com/modelcontextprotocol/typescript-sdk"},{"type":"WEB","url":"https://github.com/modelcontextprotocol/typescript-sdk/security/advisories/GHSA-cqwc-fm46-7fff"},{"type":"WEB","url":"https://github.com/modelcontextprotocol/typescript-sdk/commit/7f0cf730"},{"type":"WEB","url":"https://github.com/modelcontextprotocol/typescript-sdk/commit/b392f02ffcf37c088dbd114fedf25026ec3913d3"},{"type":"WEB","url":"https://github.com/modelcontextprotocol/typescript-sdk/releases/tag/v1.25.2"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:55.258232743Z"}}