CVE-2026-44430
MCP Registry has an unauthenticated SSRF: HTTP namespace verification dials 6to4 / NAT64 / site-local IPv6 addresses, bypassing private-address allowlist
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| go | github.com/modelcontextprotocol/registry | < 1.7.7 | 1.7.7 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Lfprojects | Mcp Registry | before 1.7.7 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-r48c-v28r-pf6v
- https://github.com/modelcontextprotocol/registry/security/advisories/GHSA-r48c-v28r-pf6v
- https://github.com/modelcontextprotocol/registry/pull/1250
- https://github.com/modelcontextprotocol/registry/commit/f5f40bd98084466eaf18fe48ea62a0d534caa774
- https://github.com/modelcontextprotocol/registry/releases/tag/v1.7.7
- https://nvd.nist.gov/vuln/detail/CVE-2026-44430