{"id":"CVE-2026-9739","revision":"915848c5e60c42118ade7cbfb9bbf16d","records":[{"revision":"915848c5e60c42118ade7cbfb9bbf16d","observedAt":"2026-10-27T16:46:14.32+00:00","statement":{"source":"nvd","id":"CVE-2026-9739","aliases":[],"title":"Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790). During the beta phase, we implemented `allowed-origins` and `allowed-hosts` flags to align with MCP security guidelines. However, the hardcoded `Access-Control-Allow-O…","description":"Vulnerable to DNS rebinding attacks when using SSE (http://b/499408790). During the beta phase, we implemented `allowed-origins` and `allowed-hosts` flags to align with MCP security guidelines. However, the hardcoded `Access-Control-Allow-Origin: *` header in the SSE initialization handler was inadvertently retained. This vulnerability specifically impacts users connecting via Toolbox using SSE under specification v2024-11-05.","state":0,"publishedAt":"2026-05-27T23:16:48.573+00:00","modifiedAt":"2026-10-26T12:10:00.13+00:00","affected":[],"metrics":[{"system":"CVSS 4.0 · cve-coordination@google.com · Secondary","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","score":9.4,"severity":"CRITICAL"}],"references":["https://github.com/googleapis/mcp-toolbox/issues/3053","https://github.com/googleapis/mcp-toolbox/pull/3054"],"sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-9739","license":"NIST NVD usage terms; underlying source attribution retained","enrichment":{"sourceStatus":"Awaiting Analysis","weaknesses":["CWE-942"],"productCriteria":[],"sourceDates":{"published":"2026-05-27T23:16:48.573","lastModified":"2026-10-26T12:10:00.130"},"relatedAdvisories":[],"note":"NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON."},"key":"nvd:CVE-2026-9739","identifiers":["CVE-2026-9739"]},"retained":false,"historicalAffected":[]}],"coverage":[]}