---
id: CVE-2026-49857
title: >-
  auth-fetch-mcp is an MCP server that lets AI assistants fetch content from
  authenticated web pages
summary: >-
  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. Ho…
severity: high
cvss: 7.4
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N'
cwe:
  - CWE-918
vendor: auth-fetch-mcp
product: auth-fetch-mcp
affected:
  - auth-fetch-mcp <= 3.0.1
patched:
  - auth-fetch-mcp 3.0.2
published: '2026-08-13'
updated: '2026-09-18'
sourceUpdated: '2026-09-18T20:09:01.757'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-49857'
references:
  - url: >-
      https://github.com/ymw0407/auth-fetch-mcp/commit/c5c523cd55b24ae1680c5bacef95d59a81ae3450
    label: security-advisories@github.com
  - url: 'https://github.com/ymw0407/auth-fetch-mcp/releases/tag/v3.0.1'
    label: security-advisories@github.com
  - url: >-
      https://github.com/ymw0407/auth-fetch-mcp/security/advisories/GHSA-pvrj-8cg3-j5f8
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-pvrj-8cg3-j5f8'
tags:
  - nvd
  - ghsa
  - npm
epss: 0.00488
epssPercentile: 0.39463
ecosystem: npm
ingestedAt: '2026-07-01T19:15:59.924Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-49857)

Affected packages:

- `auth-fetch-mcp <= 3.0.1`

Patched in:

- `auth-fetch-mcp 3.0.2`

Source: https://github.com/advisories/GHSA-pvrj-8cg3-j5f8