security: add mDNS discovery config to reduce information disclosure (#1882)

* security: add mDNS discovery config to reduce information disclosure

mDNS broadcasts can expose sensitive operational details like filesystem
paths (cliPath) and SSH availability (sshPort) to anyone on the local
network. This information aids reconnaissance and should be minimized
for gateways exposed beyond trusted networks.

Changes:
- Add discovery.mdns.enabled config option to disable mDNS entirely
- Add discovery.mdns.minimal option to omit cliPath/sshPort from TXT records
- Update security docs with operational security guidance

Minimal mode still broadcasts enough for device discovery (role, gatewayPort,
transport) while omitting details that help map the host environment.
Apps that need CLI path can fetch it via the authenticated WebSocket.

* fix: default mDNS discovery mode to minimal (#1882) (thanks @orlyjamie)

---------

Co-authored-by: theonejvo <orlyjamie@users.noreply.github.com>
Co-authored-by: Peter Steinberger <steipete@gmail.com>

docs/gateway/configuration.md

@@ -3175,6 +3175,20 @@ Auto-generated certs require `openssl` on PATH; if generation fails, the bridge
 }
 ```
 
+### `discovery.mdns` (Bonjour / mDNS broadcast mode)
+
+Controls LAN mDNS discovery broadcasts (`_clawdbot-gw._tcp`).
+
+- `minimal` (default): omit `cliPath` + `sshPort` from TXT records
+- `full`: include `cliPath` + `sshPort` in TXT records
+- `off`: disable mDNS broadcasts entirely
+
+```json5
+{
+  discovery: { mdns: { mode: "minimal" } }
+}
+```
+
 ### `discovery.wideArea` (Wide-Area Bonjour / unicast DNS‑SD)
 
 When enabled, the Gateway writes a unicast DNS-SD zone for `_clawdbot-bridge._tcp` under `~/.clawdbot/dns/` using the standard discovery domain `clawdbot.internal.`

docs/gateway/security.md

@@ -287,6 +287,49 @@ Rules of thumb:
 - If you must bind to LAN, firewall the port to a tight allowlist of source IPs; do not port-forward it broadly.
 - Never expose the Gateway unauthenticated on `0.0.0.0`.
 
+### 0.4.1) mDNS/Bonjour discovery (information disclosure)
+
+The Gateway broadcasts its presence via mDNS (`_clawdbot-gw._tcp` on port 5353) for local device discovery. In full mode, this includes TXT records that may expose operational details:
+
+- `cliPath`: full filesystem path to the CLI binary (reveals username and install location)
+- `sshPort`: advertises SSH availability on the host
+- `displayName`, `lanHost`: hostname information
+
+**Operational security consideration:** Broadcasting infrastructure details makes reconnaissance easier for anyone on the local network. Even "harmless" info like filesystem paths and SSH availability helps attackers map your environment.
+
+**Recommendations:**
+
+1. **Minimal mode** (default, recommended for exposed gateways): omit sensitive fields from mDNS broadcasts:
+   ```json5
+   {
+     discovery: {
+       mdns: { mode: "minimal" }
+     }
+   }
+   ```
+
+2. **Disable entirely** if you don't need local device discovery:
+   ```json5
+   {
+     discovery: {
+       mdns: { mode: "off" }
+     }
+   }
+   ```
+
+3. **Full mode** (opt-in): include `cliPath` + `sshPort` in TXT records:
+   ```json5
+   {
+     discovery: {
+       mdns: { mode: "full" }
+     }
+   }
+   ```
+
+4. **Environment variable** (alternative): set `CLAWDBOT_DISABLE_BONJOUR=1` to disable mDNS without config changes.
+
+In minimal mode, the Gateway still broadcasts enough for device discovery (`role`, `gatewayPort`, `transport`) but omits `cliPath` and `sshPort`. Apps that need CLI path information can fetch it via the authenticated WebSocket connection instead.
+
 ### 0.5) Lock down the Gateway WebSocket (local auth)
 
 Gateway auth is **required by default**. If no token/password is configured,