CVE-2026-49857High· 7.4▾ Twilightauth-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. Ho…
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 40.7 · likelihood 0.1 · exploitation 0
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Exploit-prediction probability, daily snapshots since Aug 14.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
0.3%
Last analysed / modified upstream
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.
Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Affected packages:
auth-fetch-mcp <= 3.0.1Patched in:
auth-fetch-mcp 3.0.2Connected by shared product, vendor, weakness, or advisory.
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