DNS rebinding attack: a victim browser that has the dashboard (or the
WhatsApp bridge) open could be tricked into fetching from an
attacker-controlled hostname that TTL-flips to 127.0.0.1. Same-origin
and CORS checks don't help — the browser now treats the attacker origin
as same-origin with the local service. Validating the Host header at
the app layer rejects any request whose Host isn't one we bound for.
Changes:
hermes_cli/web_server.py:
- New host_header_middleware runs before auth_middleware. Reads
app.state.bound_host (set by start_server) and rejects requests
whose Host header doesn't match the bound interface with HTTP 400.
- Loopback binds accept localhost / 127.0.0.1 / ::1. Non-loopback
binds require exact match. 0.0.0.0 binds skip the check (explicit
--insecure opt-in; no app-layer defence possible).
- IPv6 bracket notation parsed correctly: [::1] and [::1]:9119 both
accepted.
scripts/whatsapp-bridge/bridge.js:
- Express middleware rejects non-loopback Host headers. Bridge
already binds 127.0.0.1-only, this adds the complementary app-layer
check for DNS rebinding defence.
Tests: 8 new in tests/hermes_cli/test_web_server_host_header.py
covering loopback/non-loopback/zero-zero binds, IPv6 brackets, case
insensitivity, and end-to-end middleware rejection via TestClient.
Reported in GHSA-ppp5-vxwm-4cf7 by @bupt-Yy-young. Hardening — not
CVE per SECURITY.md §3. The dashboard's main trust boundary is the
loopback bind + session token; DNS rebinding defeats the bind assumption
but not the token (since the rebinding browser still sees a first-party
fetch to 127.0.0.1 with the token-gated API). Host-header validation
adds the missing belt-and-braces layer.
