CVE-2026-49857

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.

• CWE-918

• 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

Published

Aug 13, 2026

Last Modified

Sep 18, 2026

Status

Deferred

• One Click Account Takeover in GranolaHow a notification link broke out of Electron and led to a one-click account takeover.
• Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
• PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
• AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.

• CVE-2026-49851Mistune is a Python Markdown parser with renderers and plugi…7.5
• CVE-2026-49852joserfc is a Python library that provides an implementation …8.7
• CVE-2026-49853Tornado is a Python web framework and asynchronous networkin…7.7
• CVE-2026-49854Tornado is a Python web framework and asynchronous networkin…5.3
• CVE-2026-49855Tornado is a Python web framework and asynchronous networkin…7.5
• CVE-2026-49856@jshookmcp/jshook is an MCP server that gives AI agents tool…4.3
• CVE-2026-49858API Platform Core is a system to create hypermedia-driven RE…5.9
• CVE-2026-49859Deno is a JavaScript, TypeScript, and WebAssembly runtime. P…5.2
• CVE-2026-4986The WPForms WordPress plugin before 1.10.0.5 does not verif…5.3
• CVE-2026-49860Deno is a JavaScript, TypeScript, and WebAssembly runtime. P…5.2
• CVE-2026-49864wetty provides terminal access in browser over http/https. P…8.6
• CVE-2026-49865Kimai is an open-source time tracking application. Versions …5.3