CVE-2026-49857

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Source
https://cve.org/CVERecord?id=CVE-2026-49857
Import Source
https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-49857.json
JSON Data
https://api.osv.dev/v1/vulns/CVE-2026-49857
Aliases
Published
2026-08-13T14:50:25.324Z
Modified
2026-08-15T11:46:05.997323131Z
Severity
  • 7.4 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N CVSS Calculator
Summary
auth-fetch-mcp has SSRF Protection Bypass via IPv4-mapped IPv6 Loopback
Details

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.

Database specific 
{
    "cwe_ids": [
        "CWE-918"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/49xxx/CVE-2026-49857.json",
    "cna_assigner": "GitHub_M"
}
References

Affected packages

Git / github.com/ymw0407/auth-fetch-mcp

Affected ranges

Type
GIT
Repo
https://github.com/ymw0407/auth-fetch-mcp
Events
Introduced
0 Unknown introduced commit / All previous commits are affected
Fixed
c5c523cd55b24ae1680c5bacef95d59a81ae3450
Fixed
98f381d1298b6b7e7ff29d7a7851f18ea5f2364c
Database specific
Show details 
{
    "extracted_events": [
        {
            "introduced": "0"
        },
        {
            "fixed": "3.0.2"
        }
    ],
    "source": [
        "AFFECTED_FIELD",
        "REFERENCES"
    ]
}

Affected versions

v2.*
v2.0.4
v2.0.5
v2.0.6
v2.0.7
v2.0.8
v3.*
v3.0.0

Database specific

source 
"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-49857.json"