From 8f27520633de2ecec36b27272be6c5d7465c0e15 Mon Sep 17 00:00:00 2001 From: Patrick O'Doherty Date: Wed, 27 Mar 2024 10:10:59 -0700 Subject: [PATCH] safeweb: init (#11467) Updates https://github.com/tailscale/corp/issues/8027 Safeweb is a wrapper around http.Server & tsnet that encodes some application security defaults. Safeweb asks developers to split their HTTP routes into two http.ServeMuxs for serving browser and API-facing endpoints repsectively. It then wraps these HTTP routes with the context-appropriate security controls. safeweb.Server#Serve will serve the HTTP muxes over the provided listener. Caller are responsible for creating and tearing down their application's listeners. Applications being served over HTTPS that wish to implement HTTP redirects can use the Server#HTTPRedirect handler to do so. Signed-off-by: Patrick O'Doherty --- safeweb/http.go | 220 ++++++++++++++++++++++++++ safeweb/http_test.go | 366 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 586 insertions(+) create mode 100644 safeweb/http.go create mode 100644 safeweb/http_test.go diff --git a/safeweb/http.go b/safeweb/http.go new file mode 100644 index 000000000..9c6d33e1e --- /dev/null +++ b/safeweb/http.go @@ -0,0 +1,220 @@ +// Copyright (c) Tailscale Inc & AUTHORS +// SPDX-License-Identifier: BSD-3-Clause + +// Package safeweb provides a wrapper around an http.Server that applies +// basic web application security defenses by default. The wrapper can be +// used in place of an http.Server. A safeweb.Server adds mitigations for +// Cross-Site Request Forgery (CSRF) attacks, and annotates requests with +// appropriate Cross-Origin Resource Sharing (CORS), Content-Security-Policy, +// X-Content-Type-Options, and Referer-Policy headers. +// +// To use safeweb, the application must separate its "browser" routes from "API" +// routes, with each on its own http.ServeMux. When serving requests, the +// server will first check the browser mux, and if no matching route is found it +// will defer to the API mux. +// +// # Browser Routes +// +// All routes in the browser mux enforce CSRF protection using the gorilla/csrf +// package. The application must template the CSRF token into its forms using +// the [TemplateField] and [TemplateTag] APIs. Applications that are served in a +// secure context (over HTTPS) should also set the SecureContext field to true +// to ensure that the the CSRF cookies are marked as Secure. +// +// In addition, browser routes will also have the following applied: +// - Content-Security-Policy header that disallows inline scripts, framing, and third party resources. +// - X-Content-Type-Options header on responses set to "nosniff" to prevent MIME type sniffing attacks. +// - Referer-Policy header set to "same-origin" to prevent leaking referrer information to third parties. +// +// # API routes +// +// safeweb inspects the Content-Type header of incoming requests to the API mux +// and prohibits the use of `application/x-www-form-urlencoded` values. If the +// application provides a list of allowed origins and methods in its +// configuration safeweb will set the appropriate CORS headers on pre-flight +// OPTIONS requests served by the API mux. +// +// # HTTP Redirects +// +// The [RedirectHTTP] method returns a handler that redirects all incoming HTTP +// requests to HTTPS at the same path on the provided fully qualified domain +// name (FQDN). +// +// # Example usage +// +// h := http.NewServeMux() +// h.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) { +// fmt.Fprint(w, "Hello, world!") +// }) +// s, err := safeweb.NewServer(safeweb.Config{ +// BrowserMux: h, +// }) +// if err != nil { +// log.Fatalf("failed to create server: %v", err) +// } +// ln, err := net.Listen("tcp", ":8080") +// if err != nil { +// log.Fatalf("failed to listen: %v", err) +// } +// defer ln.Close() +// if err := s.Serve(ln); err != nil && err != http.ErrServerClosed { +// log.Fatalf("failed to serve: %v", err) +// } +// +// [TemplateField]: https://pkg.go.dev/github.com/gorilla/csrf#TemplateField +// [TemplateTag]: https://pkg.go.dev/github.com/gorilla/csrf#TemplateTag +package safeweb + +import ( + crand "crypto/rand" + "fmt" + "net" + "net/http" + "net/url" + "strings" + + "github.com/gorilla/csrf" +) + +// The default Content-Security-Policy header. +var defaultCSP = strings.Join([]string{ + `default-src 'self'`, // origin is the only valid source for all content types + `script-src 'self'`, // disallow inline javascript + `frame-ancestors 'none'`, // disallow framing of the page + `form-action 'self'`, // disallow form submissions to other origins + `base-uri 'self'`, // disallow base URIs from other origins + `block-all-mixed-content`, // disallow mixed content when serving over HTTPS + `object-src 'none'`, // disallow embedding of resources from other origins +}, "; ") + +// Config contains the configuration for a safeweb server. +type Config struct { + // SecureContext specifies whether the Server is running in a secure (HTTPS) context. + // Setting this to true will cause the Server to set the Secure flag on CSRF cookies. + SecureContext bool + + // BrowserMux is the HTTP handler for any routes in your application that + // should only be served to browsers in a primary origin context. These + // requests will be subject to CSRF protection and will have + // browser-specific headers in their responses. + BrowserMux *http.ServeMux + + // APIMux is the HTTP handler for any routes in your application that + // should only be served to non-browser clients or to browsers in a + // cross-origin resource sharing context. + APIMux *http.ServeMux + + // AccessControlAllowOrigin specifies the Access-Control-Allow-Origin header sent in response to pre-flight OPTIONS requests. + // Provide a list of origins, e.g. ["https://foobar.com", "https://foobar.net"] or the wildcard value ["*"]. + // No headers will be sent if no origins are provided. + AccessControlAllowOrigin []string + // AccessControlAllowMethods specifies the Access-Control-Allow-Methods header sent in response to pre-flight OPTIONS requests. + // Provide a list of methods, e.g. ["GET", "POST", "PUT", "DELETE"]. + // No headers will be sent if no methods are provided. + AccessControlAllowMethods []string + + // CSRFSecret is the secret used to sign CSRF tokens. It must be 32 bytes long. + // This should be considered a sensitive value and should be kept secret. + // If this is not provided, the Server will generate a random CSRF secret on + // startup. + CSRFSecret []byte +} + +func (c *Config) setDefaults() error { + if c.BrowserMux == nil { + c.BrowserMux = &http.ServeMux{} + } + + if c.APIMux == nil { + c.APIMux = &http.ServeMux{} + } + + if c.CSRFSecret == nil || len(c.CSRFSecret) == 0 { + c.CSRFSecret = make([]byte, 32) + if _, err := crand.Read(c.CSRFSecret); err != nil { + return fmt.Errorf("failed to generate CSRF secret: %w", err) + } + } + + return nil +} + +func (c Config) newHandler() http.Handler { + // only set Secure flag on CSRF cookies if we are in a secure context + // as otherwise the browser will reject the cookie + csrfProtect := csrf.Protect(c.CSRFSecret, csrf.Secure(c.SecureContext)) + + return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { + if _, p := c.BrowserMux.Handler(r); p == "" { + // disallow x-www-form-urlencoded requests to the API + if r.Header.Get("Content-Type") == "application/x-www-form-urlencoded" { + http.Error(w, "invalid content type", http.StatusBadRequest) + return + } + + // set CORS headers for pre-flight OPTIONS requests if any were configured + if r.Method == "OPTIONS" && len(c.AccessControlAllowOrigin) > 0 { + w.Header().Set("Access-Control-Allow-Origin", strings.Join(c.AccessControlAllowOrigin, ", ")) + w.Header().Set("Access-Control-Allow-Methods", strings.Join(c.AccessControlAllowMethods, ", ")) + } + c.APIMux.ServeHTTP(w, r) + return + } + + // TODO(@patrickod) consider templating additions to the CSP header. + w.Header().Set("Content-Security-Policy", defaultCSP) + w.Header().Set("X-Content-Type-Options", "nosniff") + w.Header().Set("Referer-Policy", "same-origin") + csrfProtect(c.BrowserMux).ServeHTTP(w, r) + }) +} + +// Server is a safeweb server. +type Server struct { + Config + h *http.Server +} + +// NewServer creates a safeweb server with the provided configuration. It will +// validate the configuration to ensure that it is complete and return an error +// if not. +func NewServer(config Config) (*Server, error) { + // ensure that CORS configuration is complete + corsMethods := len(config.AccessControlAllowMethods) > 0 + corsHosts := len(config.AccessControlAllowOrigin) > 0 + if corsMethods != corsHosts { + return nil, fmt.Errorf("must provide both AccessControlAllowOrigin and AccessControlAllowMethods or neither") + } + + // fill in any missing fields + if err := config.setDefaults(); err != nil { + return nil, fmt.Errorf("failed to set defaults: %w", err) + } + + return &Server{ + config, + &http.Server{Handler: config.newHandler()}, + }, nil +} + +// RedirectHTTP returns a handler that redirects all incoming HTTP requests to +// the provided fully qualified domain name (FQDN). +func (s *Server) RedirectHTTP(fqdn string) func(w http.ResponseWriter, r *http.Request) { + return func(w http.ResponseWriter, r *http.Request) { + new := url.URL{ + Scheme: "https", + Host: fqdn, + Path: r.URL.Path, + RawQuery: r.URL.RawQuery, + } + + http.Redirect(w, r, new.String(), http.StatusMovedPermanently) + } +} + +// Serve starts the server and listens on the provided listener. It will block +// until the server is closed. The caller is responsible for closing the +// listener. +func (s *Server) Serve(ln net.Listener) error { + return s.h.Serve(ln) +} diff --git a/safeweb/http_test.go b/safeweb/http_test.go new file mode 100644 index 000000000..07d921644 --- /dev/null +++ b/safeweb/http_test.go @@ -0,0 +1,366 @@ +// Copyright (c) Tailscale Inc & AUTHORS +// SPDX-License-Identifier: BSD-3-Clause + +package safeweb + +import ( + "net/http" + "net/http/httptest" + "testing" + + "github.com/gorilla/csrf" +) + +func TestCompleteCORSConfig(t *testing.T) { + _, err := NewServer(Config{AccessControlAllowOrigin: []string{"https://foobar.com"}}) + if err == nil { + t.Fatalf("expected error when AccessControlAllowOrigin is provided without AccessControlAllowMethods") + } + + _, err = NewServer(Config{AccessControlAllowMethods: []string{"GET", "POST"}}) + if err == nil { + t.Fatalf("expected error when AccessControlAllowMethods is provided without AccessControlAllowOrigin") + } + + _, err = NewServer(Config{AccessControlAllowOrigin: []string{"https://foobar.com"}, AccessControlAllowMethods: []string{"GET", "POST"}}) + if err != nil { + t.Fatalf("error creating server with complete CORS configuration: %v", err) + } +} + +func TestPostRequestContentTypeValidation(t *testing.T) { + tests := []struct { + name string + browserRoute bool + contentType string + wantErr bool + }{ + { + name: "API routes should accept `application/json` content-type", + browserRoute: false, + contentType: "application/json", + wantErr: false, + }, + { + name: "API routes should reject `application/x-www-form-urlencoded` content-type", + browserRoute: false, + contentType: "application/x-www-form-urlencoded", + wantErr: true, + }, + { + name: "Browser routes should accept `application/x-www-form-urlencoded` content-type", + browserRoute: true, + contentType: "application/x-www-form-urlencoded", + wantErr: false, + }, + { + name: "non Browser routes should accept `application/json` content-type", + browserRoute: true, + contentType: "application/json", + wantErr: false, + }, + } + + for _, tt := range tests { + t.Run(tt.name, func(t *testing.T) { + h := &http.ServeMux{} + h.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { + w.Write([]byte("ok")) + })) + var s *Server + var err error + if tt.browserRoute { + s, err = NewServer(Config{BrowserMux: h}) + } else { + s, err = NewServer(Config{APIMux: h}) + } + if err != nil { + t.Fatal(err) + } + + req := httptest.NewRequest("POST", "/", nil) + req.Header.Set("Content-Type", tt.contentType) + + w := httptest.NewRecorder() + s.h.Handler.ServeHTTP(w, req) + resp := w.Result() + if tt.wantErr && resp.StatusCode != http.StatusBadRequest { + t.Fatalf("content type validation failed: got %v; want %v", resp.StatusCode, http.StatusBadRequest) + } + }) + } +} + +func TestAPIMuxCrossOriginResourceSharingHeaders(t *testing.T) { + tests := []struct { + name string + httpMethod string + wantCORSHeaders bool + corsOrigins []string + corsMethods []string + }{ + { + name: "do not set CORS headers for non-OPTIONS requests", + corsOrigins: []string{"https://foobar.com"}, + corsMethods: []string{"GET", "POST", "HEAD"}, + httpMethod: "GET", + wantCORSHeaders: false, + }, + { + name: "set CORS headers for non-OPTIONS requests", + corsOrigins: []string{"https://foobar.com"}, + corsMethods: []string{"GET", "POST", "HEAD"}, + httpMethod: "OPTIONS", + wantCORSHeaders: true, + }, + { + name: "do not serve CORS headers for OPTIONS requests with no configured origins", + httpMethod: "OPTIONS", + wantCORSHeaders: false, + }, + } + + for _, tt := range tests { + t.Run(tt.name, func(t *testing.T) { + h := &http.ServeMux{} + h.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { + w.Write([]byte("ok")) + })) + s, err := NewServer(Config{ + APIMux: h, + AccessControlAllowOrigin: tt.corsOrigins, + AccessControlAllowMethods: tt.corsMethods, + }) + if err != nil { + t.Fatal(err) + } + + req := httptest.NewRequest(tt.httpMethod, "/", nil) + w := httptest.NewRecorder() + s.h.Handler.ServeHTTP(w, req) + resp := w.Result() + + if (resp.Header.Get("Access-Control-Allow-Origin") == "") == tt.wantCORSHeaders { + t.Fatalf("access-control-allow-origin want: %v; got: %v", tt.wantCORSHeaders, resp.Header.Get("Access-Control-Allow-Origin")) + } + }) + } +} + +func TestCSRFProtection(t *testing.T) { + tests := []struct { + name string + apiRoute bool + passCSRFToken bool + wantStatus int + }{ + { + name: "POST requests to non-API routes require CSRF token and fail if not provided", + apiRoute: false, + passCSRFToken: false, + wantStatus: http.StatusForbidden, + }, + { + name: "POST requests to non-API routes require CSRF token and pass if provided", + apiRoute: false, + passCSRFToken: true, + wantStatus: http.StatusOK, + }, + { + name: "POST requests to /api/ routes do not require CSRF token", + apiRoute: true, + passCSRFToken: false, + wantStatus: http.StatusOK, + }, + } + for _, tt := range tests { + t.Run(tt.name, func(t *testing.T) { + h := &http.ServeMux{} + h.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { + w.Write([]byte("ok")) + })) + var s *Server + var err error + if tt.apiRoute { + s, err = NewServer(Config{APIMux: h}) + } else { + s, err = NewServer(Config{BrowserMux: h}) + } + if err != nil { + t.Fatal(err) + } + + // construct the test request + req := httptest.NewRequest("POST", "/", nil) + + // send JSON for API routes, form data for browser routes + if tt.apiRoute { + req.Header.Set("Content-Type", "application/json") + } else { + req.Header.Set("Content-Type", "application/x-www-form-urlencoded") + } + + // retrieve CSRF cookie & pass it in the test request + // ref: https://github.com/gorilla/csrf/blob/main/csrf_test.go#L344-L347 + var token string + if tt.passCSRFToken { + h.Handle("/csrf", http.HandlerFunc(func(_ http.ResponseWriter, r *http.Request) { + token = csrf.Token(r) + })) + get := httptest.NewRequest("GET", "/csrf", nil) + w := httptest.NewRecorder() + s.h.Handler.ServeHTTP(w, get) + resp := w.Result() + + // pass the token & cookie in our subsequent test request + req.Header.Set("X-CSRF-Token", token) + for _, c := range resp.Cookies() { + req.AddCookie(c) + } + } + + w := httptest.NewRecorder() + s.h.Handler.ServeHTTP(w, req) + resp := w.Result() + + if resp.StatusCode != tt.wantStatus { + t.Fatalf("csrf protection check failed: got %v; want %v", resp.StatusCode, tt.wantStatus) + } + }) + } +} + +func TestContentSecurityPolicyHeader(t *testing.T) { + tests := []struct { + name string + apiRoute bool + wantCSP bool + }{ + { + name: "default routes get CSP headers", + apiRoute: false, + wantCSP: true, + }, + { + name: "`/api/*` routes do not get CSP headers", + apiRoute: true, + wantCSP: false, + }, + } + + for _, tt := range tests { + t.Run(tt.name, func(t *testing.T) { + h := &http.ServeMux{} + h.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { + w.Write([]byte("ok")) + })) + var s *Server + var err error + if tt.apiRoute { + s, err = NewServer(Config{APIMux: h}) + } else { + s, err = NewServer(Config{BrowserMux: h}) + } + if err != nil { + t.Fatal(err) + } + + req := httptest.NewRequest("GET", "/", nil) + w := httptest.NewRecorder() + s.h.Handler.ServeHTTP(w, req) + resp := w.Result() + + if (resp.Header.Get("Content-Security-Policy") == "") == tt.wantCSP { + t.Fatalf("content security policy want: %v; got: %v", tt.wantCSP, resp.Header.Get("Content-Security-Policy")) + } + }) + } +} + +func TestCSRFCookieSecureMode(t *testing.T) { + tests := []struct { + name string + secureMode bool + wantSecure bool + }{ + { + name: "CSRF cookie should be secure when server is in secure context", + secureMode: true, + wantSecure: true, + }, + { + name: "CSRF cookie should not be secure when server is not in secure context", + secureMode: false, + wantSecure: false, + }, + } + for _, tt := range tests { + t.Run(tt.name, func(t *testing.T) { + h := &http.ServeMux{} + h.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { + w.Write([]byte("ok")) + })) + s, err := NewServer(Config{BrowserMux: h, SecureContext: tt.secureMode}) + if err != nil { + t.Fatal(err) + } + + req := httptest.NewRequest("GET", "/", nil) + w := httptest.NewRecorder() + s.h.Handler.ServeHTTP(w, req) + resp := w.Result() + + cookie := resp.Cookies()[0] + if (cookie.Secure == tt.wantSecure) == false { + t.Fatalf("csrf cookie secure flag want: %v; got: %v", tt.wantSecure, cookie.Secure) + } + }) + } +} + +func TestRefererPolicy(t *testing.T) { + tests := []struct { + name string + browserRoute bool + wantRefererPolicy bool + }{ + { + name: "BrowserMux routes get Referer-Policy headers", + browserRoute: true, + wantRefererPolicy: true, + }, + { + name: "APIMux routes do not get Referer-Policy headers", + browserRoute: false, + wantRefererPolicy: false, + }, + } + + for _, tt := range tests { + t.Run(tt.name, func(t *testing.T) { + h := &http.ServeMux{} + h.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { + w.Write([]byte("ok")) + })) + var s *Server + var err error + if tt.browserRoute { + s, err = NewServer(Config{BrowserMux: h}) + } else { + s, err = NewServer(Config{APIMux: h}) + } + if err != nil { + t.Fatal(err) + } + + req := httptest.NewRequest("GET", "/", nil) + w := httptest.NewRecorder() + s.h.Handler.ServeHTTP(w, req) + resp := w.Result() + + if (resp.Header.Get("Referer-Policy") == "") == tt.wantRefererPolicy { + t.Fatalf("referer policy want: %v; got: %v", tt.wantRefererPolicy, resp.Header.Get("Referer-Policy")) + } + }) + } +}