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Medium, CVSS 6.3

MCP Registry has an unauthenticated SSRF: HTTP namespace verification dials 6to4 / NAT64 / site-local IPv6 addresses, bypassing private-address allowlist

CVE-2026-44430GHSA-r48c-v28r-pf6v

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (github.com/modelcontextprotocol/registry 1.7.7), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
6.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N · score source
EPSS
  • CVE-2026-44430: 0.29% estimated exploitation activity in the next 30 days; percentile 21.07 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary The Registry's HTTP-based namespace verification (POST /v0/auth/http, POST /v0.1/auth/http) uses safeDialContext (internal/api/handlers/v0/auth/http.go:67-110) to refuse dialling private/internal addresses when fetching the well-known public-key file from a publisher-supplied domain. The blocklist (isBlockedIP, lines 125-133) relies entirely on Go stdlib's IsLoopback / IsPrivate / IsLinkLocalUnicast / IsMulticast / IsUnspecified plus a manual CGNAT range. None of these cover IPv6 6to4 (2002::/16), NAT64 (64:ff9b::/96 and 64:ff9b:1::/48 per RFC 8215), or deprecated site-local (fec0::/10) — all of which encode arbitrary IPv4 in the address bits and tunnel to RFC1918 / cloud-metadata services on dual-stack / NAT64-enabled hosts. This is the same CWE-918 SSRF class fixed in GHSA-56c3-vfp2-5qqj on czlonkowski/n8n-mcp (CVSS 8.5 HIGH). The remediation pattern is identical: extend the blocklist with the IPv6 prefix families that embed IPv4. The endpoint is unauthenticated — it is the…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-r48c-v28r-pf6v

Agent brief

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# Patch Next advisory brief: CVE-2026-44430

Advisory: MCP Registry has an unauthenticated SSRF: HTTP namespace verification dials 6to4 / NAT64 / site-local IPv6 addresses, bypassing private-address allowlist
IDs: CVE-2026-44430, GHSA-r48c-v28r-pf6v
Record: https://patchnext.com/advisories/cve-2026-44430 (revision 1, source checked 26 Oct 2026, 15:22 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/modelcontextprotocol/registry 1.7.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/modelcontextprotocol/registry: affected < 1.7.7; fixed in 1.7.7

## Suggested inspection (read-only)
- Go github.com/modelcontextprotocol/registry: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/modelcontextprotocol/registry.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-r48c-v28r-pf6v (GitHub-reviewed advisory GHSA-r48c-v28r-pf6v lists affected ranges: Go github.com/modelcontextprotocol/registry >=0 <1.7.7)

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