The previous validator did a preflight `socket.getaddrinfo` before each
httpx request. Two problems:
* DNS rebinding / TOCTOU: httpx re-resolves at connect time, so a
hostname can answer with a public IP for the validator and a
private IP for the real request. The preflight check did not
constrain the connection.
* Event-loop blocking: `socket.getaddrinfo` is synchronous, and the
media-download callers are async. Slow resolvers stalled
unrelated requests.
Replace it with two layers, both wired automatically onto every httpx
client built by `utils.context`:
1. A request event hook running `validate_url_for_http_request`
(syntactic checks only: scheme, reserved hostnames, literal IPs,
internal TLDs). No DNS, no call-site responsibility.
2. `SSRFProtectedAsyncBackend` / `SSRFProtectedSyncBackend`, custom
httpcore network backends that resolve the hostname inside
`connect_tcp`, reject any address in a forbidden range, then
connect to that *same* validated address. The async variant uses
`loop.getaddrinfo` so it doesn't block the loop. httpcore calls
`start_tls(server_hostname=<URL host>)` after `connect_tcp`, so
TLS SNI and cert verification still use the original hostname
even though the TCP layer connects by IP.
Drop the explicit `validate_url_for_http_request(...)` calls from
`resources_handler.py` — the event hook covers them. Consolidate the
URL validator and its tests under `utils/ssrf.py` /
`tests/utils/test_ssrf.py` so the SSRF surface lives in one module.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
validate_url_for_http_request previously skipped DNS resolution, so
attacker-controlled domains that resolve to private/loopback/link-local
addresses (e.g. 127.0.0.1.nip.io) passed validation and the subsequent
httpx GET hit internal services. Resolve the hostname via getaddrinfo
and reject any result whose IP is private, loopback, link-local,
reserved, multicast, or unspecified. Unresolvable hostnames are
rejected as well.
https://claude.ai/code/session_01T335ZvA825YhuzPctmYzUy
