The HTTP namespace-verification fetcher's `isBlockedIP` composed its
blocklist from Go stdlib's `Is*` helpers plus a manual CGNAT range. That
covers IPv4 cloud metadata, RFC1918, ULA, and link-local — but Go's
classification helpers don't recognise IPv6 prefix families that embed
or tunnel to arbitrary IPv4:
- 2002::/16 RFC 3056 6to4 — bits 16-47 are an arbitrary IPv4
- 64:ff9b::/96 RFC 6052 NAT64 well-known — low 32 bits are IPv4
- 64:ff9b:1::/48 RFC 8215 NAT64 local-use — same IPv4-embedding shape
- fec0::/10 RFC 3879 site-local (deprecated, still routed by
some stacks)
On hosts with 6to4 routing or a NAT64 next-hop (the default on
IPv6-only GKE node pools, AWS IPv6-only EC2, Azure IPv6 VMs with
NAT64, and many corporate DNS64/NAT64 networks), an attacker who
controls DNS for a publisher domain can cause the registry to dial
`169.254.169.254`, `10.0.0.0/8`, etc. via the IPv6 wrapper. Same
SSRF class as GHSA-56c3-vfp2-5qqj on n8n-mcp.
Define the four prefixes via a new `mustCIDR` helper (panic on
malformed CIDR at init so a typo can't fail-open silently) and iterate
them in `isBlockedIP` after the stdlib gates. Refactor the existing
CGNAT IIFE to use the same helper for consistency. IPv4-mapped IPv6
(::ffff:0:0/96) needs no special-casing: Go's `Is*` helpers honour the
`To4()` fast-path, so e.g. `::ffff:10.0.0.1` is already classified as
`IsPrivate`.
Adds 17 test cases to `TestIsBlockedIP` covering each new prefix
family, IPv4-mapped IPv6 sanity checks, and just-outside-the-range
positive controls (`2001::1`, `2003::1`, `64:ff9c::1`).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
f5f40bd980