SSRF Vulnerability in auth-fetch-mcp Server by YMW0407
CVE-2026-49857

7.4HIGH

Key Information:

Vendor

Ymw0407

Status
Auth-fetch-mcp
Vendor
CVE Published:
13 August 2026

What is CVE-2026-49857?

The auth-fetch-mcp server has a vulnerability in version 3.0.1 related to Server-Side Request Forgery (SSRF). The implementation attempts to block requests to private and loopback addresses using a function called assertSafeUrl(). However, a flaw in the isPrivateV6() function fails to recognize IPv4-mapped IPv6 loopback addresses in their hex-normalized form. This oversight allows an attacker to exploit the vulnerability by providing a specially crafted URL, effectively bypassing the security measures in place. Consequently, the server may inadvertently connect to loopback services that should normally be inaccessible, posing a significant risk under default configurations. The issue is now resolved in version 3.0.1.

Affected Version(s)

auth-fetch-mcp < 3.0.2

References

https://github.com/ymw0407/auth-fetch-mcp/security/adviso...
x_refsource_CONFIRM
https://github.com/ymw0407/auth-fetch-mcp/commit/c5c523cd...
x_refsource_MISC
https://github.com/ymw0407/auth-fetch-mcp/releases/tag/v3...
x_refsource_MISC

CVSS V3.1

Score:
7.4
Severity:
HIGH
Confidentiality:
High
Integrity:
None
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
Required
Scope:
Changed

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.