forked from bchanot/claude
Bastien Chanot
b00e8ef442
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.