cmd/derper,tsweb: consistently add HTTP security headers (#8579)

Add a few helper functions in tsweb to add common security headers to handlers. Use those functions for all non-tailscaled-facing endpoints in derper. Signed-off-by: Andrew Lytvynov <awly@tailscale.com>
1 year ago · 96d7af3469
parent 8cda647a0f
commit 96d7af3469
3 changed files with 40 additions and 15 deletions
--- a/cmd/derper/derper.go
+++ b/cmd/derper/derper.go
@ -182,8 +182,9 @@ func main() {
 	}
 	mux.HandleFunc("/derp/probe", probeHandler)
 	go refreshBootstrapDNSLoop()
-	mux.HandleFunc("/bootstrap-dns", handleBootstrapDNS)
+	mux.HandleFunc("/bootstrap-dns", tsweb.BrowserHeaderHandlerFunc(handleBootstrapDNS))
 	mux.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		tsweb.AddBrowserHeaders(w)
 		w.Header().Set("Content-Type", "text/html; charset=utf-8")
 		w.WriteHeader(200)
 		io.WriteString(w, `<html><body>
@ -203,6 +204,7 @@ func main() {
 		}
 	}))
 	mux.Handle("/robots.txt", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		tsweb.AddBrowserHeaders(w)
 		io.WriteString(w, "User-agent: *\nDisallow: /\n")
 	}))
 	mux.Handle("/generate_204", http.HandlerFunc(serveNoContent))
@ -277,18 +279,6 @@ func main() {
 				defer tlsActiveVersion.Add(label, -1)
 			}

-			// Set HTTP headers to appease automated security scanners.
-			//
-			// Security automation gets cranky when HTTPS sites don't
-			// set HSTS, and when they don't specify a content
-			// security policy for XSS mitigation.
-			//
-			// DERP's HTTP interface is only ever used for debug
-			// access (for which trivial safe policies work just
-			// fine), and by DERP clients which don't obey any of
-			// these browser-centric headers anyway.
-			w.Header().Set("Strict-Transport-Security", "max-age=63072000; includeSubDomains")
-			w.Header().Set("Content-Security-Policy", "default-src 'none'; frame-ancestors 'none'; form-action 'none'; base-uri 'self'; block-all-mixed-content; plugin-types 'none'")
 			mux.ServeHTTP(w, r)
 		})
 		if *httpPort > -1 {
--- a/tsweb/debug.go
+++ b/tsweb/debug.go
@ -51,7 +51,7 @@ func Debugger(mux *http.ServeMux) *DebugHandler {
 	// Register this one directly on mux, rather than using
 	// ret.URL/etc, as we don't need another line of output on the
 	// index page. The /pprof/ index already covers it.
-	mux.Handle("/debug/pprof/profile", http.HandlerFunc(pprof.Profile))
+	mux.Handle("/debug/pprof/profile", BrowserHeaderHandler(http.HandlerFunc(pprof.Profile)))

 	ret.KVFunc("Uptime", func() any { return varz.Uptime() })
 	ret.KV("Version", version.Long())
@ -80,6 +80,7 @@ func (d *DebugHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}

+	AddBrowserHeaders(w)
 	f := func(format string, args ...any) { fmt.Fprintf(w, format, args...) }
 	f("<html><body><h1>%s debug</h1><ul>", version.CmdName())
 	for _, kv := range d.kvs {
@ -97,7 +98,7 @@ func (d *DebugHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 // entry in /debug/ for it.
 func (d *DebugHandler) Handle(slug, desc string, handler http.Handler) {
 	href := "/debug/" + slug
-	d.mux.Handle(href, Protected(handler))
+	d.mux.Handle(href, Protected(BrowserHeaderHandler(handler)))
 	d.URL(href, desc)
 }

--- a/tsweb/tsweb.go
+++ b/tsweb/tsweb.go
@ -423,3 +423,37 @@ func Error(code int, msg string, err error) HTTPError {
 func VarzHandler(w http.ResponseWriter, r *http.Request) {
 	varz.Handler(w, r)
 }
+
+// AddBrowserHeaders sets various HTTP security headers for browser-facing endpoints.
+//
+// The specific headers:
+//   - require HTTPS access (HSTS)
+//   - disallow iframe embedding
+//   - mitigate MIME confusion attacks
+//
+// These headers are based on
+// https://infosec.mozilla.org/guidelines/web_security
+func AddBrowserHeaders(w http.ResponseWriter) {
+	w.Header().Set("Strict-Transport-Security", "max-age=63072000; includeSubDomains")
+	w.Header().Set("Content-Security-Policy", "default-src 'self'; frame-ancestors 'none'; form-action 'none'; base-uri 'self'; block-all-mixed-content; plugin-types 'none'")
+	w.Header().Set("X-Frame-Options", "DENY")
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+}
+
+// BrowserHeaderHandler wraps the provided http.Handler with a call to
+// AddBrowserHeaders.
+func BrowserHeaderHandler(h http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		AddBrowserHeaders(w)
+		h.ServeHTTP(w, r)
+	})
+}
+
+// BrowserHeaderHandlerFunc wraps the provided http.HandlerFunc with a call to
+// AddBrowserHeaders.
+func BrowserHeaderHandlerFunc(h http.HandlerFunc) http.HandlerFunc {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		AddBrowserHeaders(w)
+		h.ServeHTTP(w, r)
+	})
+}