{"cve":"CVE-2026-49857","nvd":{"published":"2026-08-13T15:19:41.743","modified":"2026-10-24T16:10:00.153","status":"Deferred","description":"auth-fetch-mcp is an MCP server that lets AI assistants fetch content from authenticated web pages. Version 3.0.1 implements SSRF protection in `assertSafeUrl()` (`src/security.ts`) to block requests to private and loopback addresses. However, the `isPrivateV6()` function fails to detect IPv4-mapped IPv6 loopback addresses in their hex-normalized form. When an attacker supplies a URL such as `http://[::ffff:127.0.0.1]:PORT/`, the Node.js WHATWG URL parser silently normalizes the host to `[::ffff:7f00:1]`. Because `net.isIPv4('7f00:1')` returns `false`, the private-IP check is bypassed and the URL is passed to the browser or HTTP client, allowing the MCP tool to reach loopback services that are supposed to be blocked. The issue is exploitable under default configuration without any special environment variable. Version 3.0.1 patches the issue.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N","score":7.4},"cwes":["CWE-918"],"references":["https://github.com/ymw0407/auth-fetch-mcp/commit/c5c523cd55b24ae1680c5bacef95d59a81ae3450","https://github.com/ymw0407/auth-fetch-mcp/releases/tag/v3.0.1","https://github.com/ymw0407/auth-fetch-mcp/security/advisories/GHSA-pvrj-8cg3-j5f8"],"products":[],"source":"nvd","synced_at":"2026-10-24T16:53:35.584907681+00:00"},"epss":{"cve":"CVE-2026-49857","score":0.00488,"percentile":0.41743,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-pvrj-8cg3-j5f8","url":"https://osv.dev/vulnerability/GHSA-pvrj-8cg3-j5f8","summary":"auth-fetch-mcp has SSRF Protection Bypass via IPv4-mapped IPv6 Loopback","modified":"2026-07-01T18:41:31.529770Z","packages":[{"ecosystem":"npm","name":"auth-fetch-mcp","purl":"pkg:npm/auth-fetch-mcp","ranges":["<3.0.2"],"fixed":["3.0.2"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}