diff --git a/Changelog.md b/Changelog.md
index a345cc5..44b2654 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -4,6 +4,7 @@
 
 ### Changed
 
+- Deny WebSocket connections from unknown origins
 - Let firmware update command look for bootloader if no Senso in regular mode is found
 - Update build system and development environment
 
diff --git a/src/dividat-driver/flex/websocket.go b/src/dividat-driver/flex/websocket.go
index 3427073..bbec7c8 100644
--- a/src/dividat-driver/flex/websocket.go
+++ b/src/dividat-driver/flex/websocket.go
@@ -124,6 +124,7 @@ var webSocketUpgrader = websocket.Upgrader{
 	ReadBufferSize:  1024,
 	WriteBufferSize: 1024,
 	CheckOrigin: func(r *http.Request) bool {
+		// Check is performed by top-level HTTP middleware, and not repeated here.
 		return true
 	},
 }
diff --git a/src/dividat-driver/senso/websocket.go b/src/dividat-driver/senso/websocket.go
index 4d0bb72..833c9e0 100644
--- a/src/dividat-driver/senso/websocket.go
+++ b/src/dividat-driver/senso/websocket.go
@@ -323,6 +323,7 @@ var webSocketUpgrader = websocket.Upgrader{
 	ReadBufferSize:  1024,
 	WriteBufferSize: 1024,
 	CheckOrigin: func(r *http.Request) bool {
+		// Check is performed by top-level HTTP middleware, and not repeated here.
 		return true
 	},
 }
diff --git a/src/dividat-driver/server/main.go b/src/dividat-driver/server/main.go
index 33a4425..94f5bfe 100644
--- a/src/dividat-driver/server/main.go
+++ b/src/dividat-driver/server/main.go
@@ -26,7 +26,6 @@ func Start(logger *logrus.Logger, origins []string) context.CancelFunc {
 	// Log Server
 	logServer := logging.NewLogServer()
 	logger.AddHook(logServer)
-	http.Handle("/log", corsHeaders(origins, logServer))
 
 	baseLog := logger.WithFields(logrus.Fields{
 		"version": version,
@@ -46,22 +45,25 @@ func Start(logger *logrus.Logger, origins []string) context.CancelFunc {
 
 	baseLog.Info("Dividat Driver starting")
 
+	// Setup log endpoint
+	http.Handle("/log", originMiddleware(origins, baseLog, logServer))
+
 	// Setup a context
 	ctx, cancel := context.WithCancel(context.Background())
 
 	// Setup Senso
 	sensoHandle := senso.New(ctx, baseLog.WithField("package", "senso"))
-	http.Handle("/senso", corsHeaders(origins, sensoHandle))
+	http.Handle("/senso", originMiddleware(origins, baseLog, sensoHandle))
 
 	// Setup SensingTex reader
 	flexHandle := flex.New(ctx, baseLog.WithField("package", "flex"))
-	http.Handle("/flex", corsHeaders(origins, flexHandle))
+	http.Handle("/flex", originMiddleware(origins, baseLog, flexHandle))
 
 	// Setup RFID scanner
 	rfidHandle := rfid.NewHandle(ctx, baseLog.WithField("package", "rfid"))
 	// net/http performs a redirect from `/rfid` if only `/rfid/` is mounted
-	http.Handle("/rfid", corsHeaders(origins, rfidHandle))
-	http.Handle("/rfid/", corsHeaders(origins, rfidHandle))
+	http.Handle("/rfid", originMiddleware(origins, baseLog, rfidHandle))
+	http.Handle("/rfid/", originMiddleware(origins, baseLog, rfidHandle))
 
 	// Create a logger for server
 	log := baseLog.WithField("package", "server")
@@ -80,7 +82,7 @@ func Start(logger *logrus.Logger, origins []string) context.CancelFunc {
 		"os":        systemInfo.Os,
 		"arch":      systemInfo.Arch,
 	})
-	http.Handle("/", corsHeaders(origins, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	http.Handle("/", originMiddleware(origins, baseLog, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")
 		w.Write(rootMsg)
 	})))
@@ -107,17 +109,34 @@ func Start(logger *logrus.Logger, origins []string) context.CancelFunc {
 	return cancel
 }
 
-// Middleware for CORS headers, to be applied to any route that should be accessible from browser apps.
-func corsHeaders(origins []string, next http.Handler) http.Handler {
+// Middleware to ensure browser requests come from permissible origins.
+//
+// This protects anyone running the driver from malicious websites connecting
+// to the loopback address. In order to protect WebSocket endpoints, for which
+// CORS pre-flight requests are not performed, we fully deny requests from
+// unknown origins instead of just withholding CORS headers.
+func originMiddleware(origins []string, log *logrus.Entry, next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if len(r.Header["Origin"]) == 1 && contains(origins, r.Header["Origin"][0]) {
-			w.Header().Set("Access-Control-Allow-Origin", r.Header["Origin"][0])
+		origin := r.Header.Get("Origin")
+
+		// Check whether a request was made from a permissible origin.
+		// An absent Origin header indicates a non-browser request and is permissible.
+		if origin != "" && !contains(origins, origin) {
+			log.WithField("origin", r.Header.Get("Origin")).Info("Denying request from untrusted origin.")
+			w.WriteHeader(403)
+			return
+		}
+
+		// Set CORS/Private Network Access headers
+		if origin != "" {
+			w.Header().Set("Access-Control-Allow-Origin", origin)
 			w.Header().Set("Access-Control-Allow-Private-Network", "true")
 		}
 
 		// Announce that `Origin` header value may affect response
 		w.Header().Set("Vary", "Origin")
 
+		// Greenlight pre-flight requests, forward all other requests
 		if r.Method == "OPTIONS" {
 			w.WriteHeader(200)
 			return
diff --git a/test/cors.js b/test/cors.js
new file mode 100644
index 0000000..7e835a2
--- /dev/null
+++ b/test/cors.js
@@ -0,0 +1,89 @@
+/* eslint-env mocha */
+
+const { wait, getJSON, startDriver, connectWS } = require('./utils')
+const expect = require('chai').expect
+
+const httpEndpoints = [
+  'http://127.0.0.1:8382',
+  'http://127.0.0.1:8382/log',
+  'http://127.0.0.1:8382/rfid/readers'
+]
+
+const wsEndpoints = [
+  'ws://127.0.0.1:8382/senso',
+  'ws://127.0.0.1:8382/flex'
+]
+
+const permissibleOrigins = [ 'https://test-origin.xyz', 'http://127.0.0.1:8000' ]
+const untrustedOrigin = 'https://foreign-origin.xyz'
+
+let driver
+
+beforeEach(async () => {
+  let code = 0
+  driver = startDriver(...permissibleOrigins.flatMap(origin => [ '--permissible-origin', origin ])).on('exit', (c) => {
+    code = c
+  })
+  await wait(500)
+  expect(code).to.be.equal(0)
+  driver.removeAllListeners()
+})
+
+afterEach(() => {
+  driver.kill()
+})
+
+// No `Origin` header
+
+it('can make HTTP requests with no origin set', async () => {
+  return Promise.all(httpEndpoints.map(url =>
+    fetch(url).then((response) => { expect(response.status, `GET ${url}`).to.equal(200) })
+  ))
+})
+
+it('can connect to WebSocket endpoints with no origin set', async () => {
+  return Promise.all(wsEndpoints.map(async (url) => {
+    let connected = await connectWS(url).then(_ => true).catch(_ => false)
+    expect(connected, `WS ${url}`).to.be.true
+  }))
+})
+
+// Known `Origin` header
+
+it('can make HTTP requests with known origin set', async () => {
+  return Promise.all(httpEndpoints.flatMap(url =>
+    permissibleOrigins.map(origin =>
+      fetch(url, { headers: { Origin: origin } }).then((response) => {
+        expect(response.status, `GET ${url} (Origin: ${origin})`).to.equal(200)
+        expect(response.headers.get('Access-Control-Allow-Origin'), `Access-Control-Allow-Origin ${url}`).to.equal(origin)
+        expect(response.headers.get('Access-Control-Allow-Private-Network'), `Access-Control-Allow-Private-Network ${url}`).to.equal('true')
+      })
+    )
+  ))
+})
+
+it('can connect to WebSocket endpoints with known origin set', async () => {
+  return Promise.all(wsEndpoints.flatMap(url =>
+    permissibleOrigins.map(async (origin) => {
+      let connected = await connectWS(url, { headers: { Origin: origin } }).then(_ => true).catch(_ => false)
+      expect(connected, `WS ${url} (Origin: ${origin})`).to.be.true
+    })
+  ))
+})
+
+// Unknown `Origin` header
+
+it('can not make HTTP requests with unknown origin set', async () => {
+  return Promise.all(httpEndpoints.map(url =>
+    fetch(url, { headers: { Origin: untrustedOrigin } }).then((response) => {
+      expect(response.status, `GET ${url}`).to.equal(403)
+    })
+  ))
+})
+
+it('can not connect to WebSocket endpoints with unknown origin set', async () => {
+  return Promise.all(wsEndpoints.map(async (url) => {
+    let connected = await connectWS(url, { headers: { Origin: untrustedOrigin } }).then(_ => true).catch(_ => false)
+    expect(connected, `WS ${url}`).to.be.false
+  }))
+})
diff --git a/test/index.js b/test/index.js
index d41eac9..9302ff0 100644
--- a/test/index.js
+++ b/test/index.js
@@ -3,11 +3,14 @@ describe('General functionality', () => {
   require('./general')
 })
 
+describe('CORS and PNA protection', () => {
+  require('./cors')
+})
+
 describe('Senso', () => {
   require('./senso')
 })
 
-
 describe('RFID', () => {
   require('./rfid')
 })
diff --git a/test/utils.js b/test/utils.js
index 5613efd..2a92ce2 100644
--- a/test/utils.js
+++ b/test/utils.js
@@ -10,15 +10,15 @@ module.exports = {
     })
   },
 
-  startDriver: function () {
-    return spawn('bin/dividat-driver')
+  startDriver: function (...args) {
+    return spawn('bin/dividat-driver', args)
     // useful for debugging:
     // return spawn('bin/dividat-driver', [], {stdio: 'inherit'})
   },
 
-  connectWS: function (url) {
+  connectWS: function (url, opts) {
     return new Promise((resolve, reject) => {
-      const ws = new WebSocket(url)
+      const ws = new WebSocket(url, opts)
       ws.on('open', () => {
         ws.removeAllListeners()
         resolve(ws)