Most recent entries from all

EUVD-2026-319038

fkie_cve-2026-44430

The MCP Registry provides MCP clients with a list of MCP servers, like an app store for MCP servers. Prior to 1.7.7, 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 vulnerability is fixed in 1.7.7.

GHSA-r48c-v28r-pf6v — MCP Registry has an unauthenticated SSRF: HTTP namespace verification dials 6to4 / NAT64 / site-local IPv6 addresses, b…

Affected: Go: github.com/modelcontextprotocol/registry

### 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 login flow itself — so attack complexity is low aside from the host-level routing dependency.

Affected: latest `main` HEAD `23f4fda` and current production `v1.7.6` deployment at `https://registry.modelcontextprotocol.io/v0/auth/http`.

### Details

#### Vulnerable code

`internal/api/handlers/v0/auth/http.go:125-133`:

```go func isBlockedIP(ip net.IP) bool { if ip == nil { return true } return ip.IsLoopback() || ip.IsPrivate() ||…