By-principle hardening. H1's url-guard validates the NAME; urlopen then resolved
AND connected — two DNS lookups with a window a hostile authority uses to answer
PUBLIC to validation and PRIVATE (169.254.169.254 metadata, 127.0.0.1, the LAN)
to the connect. A name-level guard cannot see that rebind.
safe_fetch collapses the two lookups into one: resolve ONCE, validate every IP
(ipaddress, dual-stack v4+v6), refuse if ANY is non-public (the multi-A vector),
connect to the exact validated IP with Host+SNI+cert for the real host — no
second resolution to poison. Redirects re-validate each hop (urlopen followed
them blind). One seam: sitemap._fetch, which linkgraph/render_check/drift all
call, so every network verb inherits it.
The load-bearing property (confirmed by the security review): classification is
on the OS-resolved address (sockaddr[0]), never the URL text — so octal/hex/
decimal literals, IPv4-mapped IPv6, NAT64, 6to4 are all defeated structurally,
not by enumeration.
Better than the source idea (claude-seo url_safety.py, MIT): dual-stack (theirs
IPv4-only), no global monkeypatch so thread-safe by construction (theirs locks a
patched getaddrinfo), stdlib-only (no requests). Proven end-to-end before
writing: pinned connect keeps SNI+cert for the real host.
NOT covered, stated not silent: shell `curl` in the agent specs (separate
process, unpinnable here). Smaller surface; `curl --resolve` is a separate change.
REVIEW-SURFACED (fresh security-auditor, adversarial, VERDICT PASS) — two real
holes it found while attacking the diff, both fixed here:
- billion-laughs REOPENED in C1b: _refuse_dtd scanned only raw[:4096], so a
>4KB leading comment pushed <!DOCTYPE past the window while ET parsed AND
EXPANDED the entities. Proven (&lol2; → "lollollollollol"), now a full-doc
case-insensitive scan. This is a genuine fix to already-merged C1b, not this
feature — fixed here rather than filed, per root-cause discipline.
- 192.88.99.0/24 (6to4-relay anycast) passed is_global as public — added to an
extra special-use deny list.
Verified: rebind-to-metadata refused BEFORE any connect (injected resolver),
multi-A public+private refused, classifier fuzzed dual-stack incl. CGNAT/6to4,
non-http scheme refused, both review fixes proven with no false positive; real
fetch still works (zenquality 86 loc, lavageangels 24) through the pinned path;
all 4 verbs work end-to-end via fetch.sh; seo-data 210 → 221 pass, 0 fail; full
suite green; shellcheck + py_compile clean.
