CVE-2026-49857Public exploitNetwork attack vector

Internal response disclosure via IPv4-mapped IPv6 bypass

Published Aug 13, 2026 · Updated Aug 13, 2026

SSRF in auth-fetch-mcp 3.0.1 and earlier allows remote attackers to read internal HTTP responses through crafted MCP tool URLs. The isPrivateV6 check treats a hex-normalized IPv4-mapped IPv6 loopback suffix as non-IPv4, so assertSafeUrl passes the address to the browser or HTTP client. Exploitation requires control of auth_fetch or download_media URL input and user interaction for auth_fetch; it discloses reachable internal responses without directly altering or interrupting services.

CVSS severity7.4
High
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSRF in auth-fetch-mcp 3.0.1 and earlier allows remote attackers to read internal HTTP responses through crafted MCP tool URLs. The isPrivateV6 check treats a hex-normalized IPv4-mapped IPv6 loopback suffix as non-IPv4, so assertSafeUrl passes the address to the browser or HTTP client. Exploitation requires control of auth_fetch or download_media URL input and user interaction for auth_fetch; it discloses reachable internal responses without directly altering or interrupting services.

The record

CVE
CVE-2026-49857
Published
Aug 13, 2026
Updated
Aug 13, 2026
Vendor
Minwoo Yun
Product
auth-fetch-mcp
Classifications
CWE-918, T1552.005
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 13, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.0.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Minwoo Yun · auth-fetch-mcpversion=< 3.0.2

Published CVSS scores

7.4GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
T1552.005Unsecured Credentials Cloud Instance Metadata API

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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