{"id":"CVE-2026-44427","aliases":["GHSA-v8vw-gw5j-w7m6","GO-2026-5658"],"url":"https://o3.security/vulnerability/CVE-2026-44427","summary":"MCP Registry: Open Redirect","details":"### Summary\nThe TrailingSlashMiddleware in internal/api/server.go is vulnerable to an open redirect attack. An attacker can craft a URL with a protocol-relative path (e.g., //evil.com/) that, after trailing slash removal, results in a Location header of //evil.com — which browsers interpret as an absolute URL to an external domain.\n\n### Details\nThe TrailingSlashMiddleware strips trailing slashes from request paths and issues a 308 Permanent Redirect to the cleaned path. However, it does not validate or sanitize the resulting path before using it as the redirect target.\n\nWhen a request is made with a path like //evil.com/, the middleware processes it as follows:\n\n### PoC\n1. Start the registry server locally or identify a deployed instance\n2. Send a request with a double-slash path followed by an external domain:\n`curl -v https://<registry-host>//evil.com/`\n<img width=\"3066\" height=\"969\" alt=\"image\" src=\"https://github.com/user-attachments/assets/a5305f00-29bf-4708-952a-478d608f2074\" />\n3. Observe the 308 Permanent Redirect response with Location: //evil.com:\n4. When accessed in a browser, the user is redirected to https://evil.com\n\n\n\n### Impact\n**Phishing**: Attackers can abuse the trusted registry domain to redirect users to credential-harvesting pages\n**Malware distribution**: Redirect users to sites serving malicious downloads\n**Trust abuse:** Links originating from the official MCP Registry domain carry implicit trust","published":"2026-05-14T21:07:34.364Z","modified":"2026-08-12T03:51:47.823869564Z","cvss":null,"epss":{"score":0.0041,"percentile":0.33778,"asOf":"2026-08-24"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/modelcontextprotocol/registry","fixedVersion":"1.7.5"}],"fix":{"url":"https://github.com/modelcontextprotocol/registry/pull/1227","label":"modelcontextprotocol/registry#1227"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44427.json"},{"type":"ADVISORY","url":"https://github.com/modelcontextprotocol/registry/security/advisories/GHSA-v8vw-gw5j-w7m6"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-44427"},{"type":"WEB","url":"https://github.com/modelcontextprotocol/registry/pull/1227"},{"type":"WEB","url":"https://github.com/modelcontextprotocol/registry/commit/1201cbd82b2cf6d4b56edfc05c763059a12f9fdb"},{"type":"PACKAGE","url":"https://github.com/modelcontextprotocol/registry"},{"type":"WEB","url":"https://github.com/modelcontextprotocol/registry/releases/tag/v1.7.5"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:47.823869564Z"}}