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Shankar
371b9836e0
The webhook notifier would previously accept any operator-configured URL
and hand it to http.Client without validation. That exposed two
SSRF classes (CWE-918):
* Reserved-address reachability — a misconfigured or adversarial
webhook URL pointing at 127.0.0.1, ::1, 169.254.169.254 (cloud
metadata), or 0.0.0.0 would succeed, exfiltrating request bodies
to local services or leaking short-lived cloud credentials.
* DNS rebinding — a hostname resolving to a public IP at validation
time and to a reserved IP at dial time would bypass any
URL-string-only check.
Fix installs two independent layers:
* validation.ValidateSafeURL runs at config-ingest time and before
every outbound POST. It rejects non-HTTP(S) schemes, empty hosts,
and literal reserved-IP hosts with a clear operator-facing error.
This is a fast early diagnostic.
* validation.SafeHTTPDialContext is installed on the webhook
http.Transport. It re-resolves the host at dial time, rejects any
resolved address whose address lies in a reserved range (loopback,
link-local, multicast, broadcast, unspecified, IPv6
link-local/multicast), and pins the resolved IP into the final
dial address so the TLS handshake targets the exact IP the guard
approved. This is the authoritative, TOCTOU-safe defence against
DNS rebinding.
The two layers are complementary — validateURL fails fast on obvious
misconfiguration; SafeHTTPDialContext fails closed when DNS changes
between validation and dial.
The existing unexported isReservedIP helper in
internal/service/network_scan.go is extracted into
internal/validation.IsReservedIP with byte-identical behaviour so the
webhook notifier and the network scanner share a single authoritative
reserved-address list. RFC 1918 ranges remain intentionally allowed
(certctl's self-hosted design). Broader unspecified / IPv6 link-local
coverage lives only in the stricter dial-time policy, where it belongs
for outbound HTTP egress.
Test seam: Connector gains an unexported validateURL func field and a
same-package newForTest constructor that installs a permissive
validator and the stdlib default transport. Production callers cannot
reach this constructor because it is unexported; only same-package
tests (package webhook) can use it. Same-package happy-path tests call
newForTest so they can point at httptest loopback servers without
being blocked by the production guard. The four SSRF-rejection tests
that verify the guard itself still call New so they exercise the real,
strict validator. This keeps the production SSRF defence
unconditionally on in real code while preserving legitimate unit-test
coverage.
Tests
-----
* internal/validation/ssrf_test.go (new) — 16-subtest pin on
IsReservedIP that is byte-identical with the original network-
scanner behaviour; ValidateSafeURL accept/reject matrix covering
HTTPS/HTTP, reserved-literal IPv4/IPv6, dangerous schemes
(file/gopher/ftp/javascript/data/ldap/dict/jar), missing hosts,
and malformed inputs; SafeHTTPDialContext rejects literal reserved
addresses and hosts resolving to reserved addresses (DNS-rebinding
coverage via localhost).
* internal/connector/notifier/webhook/webhook_test.go — happy-path
tests switched to newForTest; production-guard SSRF-rejection
tests (TestValidateConfig_RejectsReservedURLs,
TestValidateConfig_RejectsDangerousScheme,
TestPostWebhook_RejectsReservedURL,
TestPostWebhook_RejectsDangerousScheme) continue to call New so
they exercise the unconditionally-installed production validator.
Wire-format invariants preserved
--------------------------------
* Outbound HTTP request shape (method, headers, body, HMAC
signature) unchanged.
* network_scan.go behaviour unchanged — validation.IsReservedIP is
byte-identical with the deleted helper.
* RFC 1918 (10/8, 172.16/12, 192.168/16) remain allowed for both
outbound webhook and CIDR expansion, matching the self-hosted
design.
Verification
------------
* go test -race ./internal/validation/... ./internal/connector/
notifier/webhook/... ./internal/service/... — green.
* Full-suite go test -race ./... — green (GOTMPDIR=/dev/shm to
sidestep full /tmp on the sandbox host).
* Coverage gates pass: service 68.8% >= 55%, handler 83.6% >= 60%,
domain 82.0% >= 40%, middleware 63.8% >= 30%. Overall 67.8%.
Webhook package 91.5% line coverage; validation package
ValidateSafeURL/SafeHTTPDialContext 78-100% per function.
* govulncheck ./... — no vulnerabilities found.
* golangci-lint run on touched H-4 production code — clean. Pre-
existing errcheck/gosimple warnings in scope-adjacent files
(webhook_test.go:270 w.Write, network_scan.go:120/173/265/305)
verified against 9e957c3 to predate this commit; left alone per
scope guard.
Operational notes
-----------------
* No migration needed. The guard is pure Go code; existing webhook
configs continue to work unless they point at reserved addresses,
in which case they now fail closed with a clear error.
* Existing operators who rely on webhook POST to 127.0.0.1 or
::1 (e.g., local receivers on the same host as certctl-server)
must expose their receiver on an RFC 1918 address or public IP.
This is deliberate — the threat model for webhook notifiers
includes untrusted operator-supplied URLs.
Scope guard: H-4 only. H-5, H-6, M-*, L-*, and I-* findings remain
open and are tracked separately. No drive-by refactors.