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CVE-2026-49857— auth-fetch-mcp has SSRF Protection Bypass via IPv4-mapped IPv6 Loopback

CVSS 7.4 · High

Possible ATT&CK Techniques 1AI

T1071.001 · Web Protocols

Affected Version Matrix 1

VendorProductVersion RangeStatus
ymw0407auth-fetch-mcp< 3.0.2affected
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I. Basic Information for CVE-2026-49857

Vulnerability Information
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Vulnerability Title
auth-fetch-mcp has SSRF Protection Bypass via IPv4-mapped IPv6 Loopback
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
服务端请求伪造(SSRF)
Source: CVE Program / CVE List V5

Affected Products

VendorProductAffected VersionsCPESubscribe
ymw0407auth-fetch-mcp < 3.0.2 -

II. Public POCs for CVE-2026-49857

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III. Intelligence Information for CVE-2026-49857

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Patches & Fixes for CVE-2026-49857 (1)

Vendor Advisories for CVE-2026-49857 (1)

Other References for CVE-2026-49857 (1)

IV. Related Vulnerabilities

Same weakness: CWE-918

V. Comments for CVE-2026-49857

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