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safeweb: replace gorilla with Sec-Fetch-Site check

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Require that all non-(GET|OPTIONS|HEAD) requests to the browser mux
specify Sec-Fetch-Site=same-origin to prohibit cross-origin requests.

Optionally allow for requests to specify "same-site" indicating a
cross-origin request from an origin that shares a root domain with the
application's own.

Updates tailscale/corp#25340
This commit is contained in:
Patrick O'Doherty 2025-04-17 17:24:48 -07:00
parent e649227ef2
commit 4a39a47248
No known key found for this signature in database
2 changed files with 108 additions and 128 deletions
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95
safeweb/http.go
View File

@ -15,11 +15,9 @@
//
// # 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.
// All routes in the browser mux are protected against CSRF attacks by
// requiring non-(GET|HEAD|OPTIONS) requests to specify the Sec-Fetch-Site header
// with the value "same-origin".
//
// In addition, browser routes will also have the following applied:
// - Content-Security-Policy header that disallows inline scripts, framing, and third party resources.
@ -64,15 +62,11 @@
// 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 (
"cmp"
"context"
crand "crypto/rand"
"fmt"
"log"
"maps"
@ -82,8 +76,6 @@ import (
"path"
"slices"
"strings"
"github.com/gorilla/csrf"
)
// CSP is the value of a Content-Security-Policy header. Keys are CSP
@ -150,10 +142,6 @@ var DefaultStrictTransportSecurityOptions = "max-age=31536000"
// 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
@ -174,12 +162,6 @@ type Config struct {
// 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
// CSP is the Content-Security-Policy header to return with BrowserMux
// responses.
CSP CSP
@ -188,10 +170,6 @@ type Config struct {
// inline CSS.
CSPAllowInlineStyles bool
// CookiesSameSiteLax specifies whether to use SameSite=Lax in cookies. The
// default is to set SameSite=Strict.
CookiesSameSiteLax bool
// StrictTransportSecurityOptions specifies optional directives for the
// Strict-Transport-Security header sent in response to requests made to the
// BrowserMux when SecureContext is true.
@ -203,6 +181,16 @@ type Config struct {
// Do not use the Handler field of http.Server, as it will be ignored.
// Instead, set your handlers using APIMux and BrowserMux.
HTTPServer *http.Server
// ServeHSTS specifies whether to serve the Strict-Transport-Security header
// in response to requests made to the BrowserMux.
ServeHSTS bool
// AllowSecFetchSiteSameSite specifies whether to allow requests with the
// Sec-Fetch-Site header set to "same-site " indicating that they are
// cross-origin but that their origin shares the same site (gTLD+1) with
// that of the request.
AllowSecFetchSiteSameSite bool
}
func (c *Config) setDefaults() error {
@ -214,13 +202,6 @@ func (c *Config) setDefaults() error {
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)
}
}
if c.CSP == nil {
c.CSP = DefaultCSP()
}
@ -231,9 +212,8 @@ func (c *Config) setDefaults() error {
// Server is a safeweb server.
type Server struct {
Config
h *http.Server
csp string
csrfProtect func(http.Handler) http.Handler
h *http.Server
csp string
}
// NewServer creates a safeweb server with the provided configuration. It will
@ -252,10 +232,6 @@ func NewServer(config Config) (*Server, error) {
return nil, fmt.Errorf("failed to set defaults: %w", err)
}
sameSite := csrf.SameSiteStrictMode
if config.CookiesSameSiteLax {
sameSite = csrf.SameSiteLaxMode
}
if config.CSPAllowInlineStyles {
if _, ok := config.CSP["style-src"]; ok {
config.CSP.Add("style-src", "unsafe-inline")
@ -266,9 +242,6 @@ func NewServer(config Config) (*Server, error) {
s := &Server{
Config: config,
csp: config.CSP.String(),
// 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(config.CSRFSecret, csrf.Secure(config.SecureContext), csrf.SameSite(sameSite)),
}
s.h = cmp.Or(config.HTTPServer, &http.Server{})
if s.h.Handler != nil {
@ -318,12 +291,6 @@ func checkHandlerType(apiPattern, browserPattern string) handlerType {
}
func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// if we are not in a secure context, signal to the CSRF middleware that
// TLS-only header checks should be skipped
if !s.Config.SecureContext {
r = csrf.PlaintextHTTPRequest(r)
}
_, bp := s.BrowserMux.Handler(r)
_, ap := s.APIMux.Handler(r)
switch {
@ -376,10 +343,38 @@ func (s *Server) serveBrowser(w http.ResponseWriter, r *http.Request) {
w.Header().Set("Content-Security-Policy", s.csp)
w.Header().Set("X-Content-Type-Options", "nosniff")
w.Header().Set("Referer-Policy", "same-origin")
if s.SecureContext {
if s.ServeHSTS {
w.Header().Set("Strict-Transport-Security", cmp.Or(s.StrictTransportSecurityOptions, DefaultStrictTransportSecurityOptions))
}
s.csrfProtect(s.BrowserMux).ServeHTTP(w, r)
// Allow GET, HEAD, and OPTIONS requests to the browser mux without
// Sec-Fetch-Site header checks.
switch r.Method {
case "GET", "HEAD", "OPTIONS":
s.BrowserMux.ServeHTTP(w, r)
return
default:
}
switch r.Header.Get("Sec-Fetch-Site") {
case "same-origin":
// allow same-origin requests
case "same-site":
// allow cross-origin, but same-site requests if configured
if !s.AllowSecFetchSiteSameSite {
http.Error(w, "forbidden cross-origin request", http.StatusForbidden)
return
}
case "cross-site", "none":
// deny cross-site requests or direct navigation non-GET requests.
http.Error(w, "forbidden cross-origin request", http.StatusForbidden)
return
default:
// deny requests with no Sec-Fetch-Site header
http.Error(w, "missing required Sec-Fetch-Site header. You might need to update your browser.", http.StatusForbidden)
return
}
s.BrowserMux.ServeHTTP(w, r)
}
// ServeRedirectHTTP serves a single HTTP handler on the provided listener that

141
safeweb/http_test.go
View File

@ -13,7 +13,6 @@ import (
"time"
"github.com/google/go-cmp/cmp"
"github.com/gorilla/csrf"
)
func TestCompleteCORSConfig(t *testing.T) {
@ -156,28 +155,62 @@ func TestAPIMuxCrossOriginResourceSharingHeaders(t *testing.T) {
func TestCSRFProtection(t *testing.T) {
tests := []struct {
name string
apiRoute bool
passCSRFToken bool
wantStatus int
name string
httpMethod string
apiRoute bool
secFetchSiteNone bool
secFetchSiteSameOrigin bool
secFetchSiteSameSite bool
secFetchSiteCrossSite bool
permitSameSite 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: "GET requests to browser routes do not require Sec-Fetch-Site header",
httpMethod: http.MethodGet,
apiRoute: false,
wantStatus: http.StatusOK,
},
{
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 browser routes require Sec-Fetch-Site=same-origin and fail if not provided",
httpMethod: http.MethodPost,
apiRoute: false,
wantStatus: http.StatusForbidden,
},
{
name: "POST requests to /api/ routes do not require CSRF token",
apiRoute: true,
passCSRFToken: false,
wantStatus: http.StatusOK,
name: "POST requests to browser routes require Sec-Fetch-Site=same-origin and pass if provided",
secFetchSiteSameOrigin: true,
httpMethod: http.MethodPost,
apiRoute: false,
wantStatus: http.StatusOK,
},
{
name: "POST requests to browser routes with Sec-Fetch-Site=none fail",
secFetchSiteNone: true,
httpMethod: http.MethodPost,
apiRoute: false,
wantStatus: http.StatusForbidden,
},
{
name: "POST requests to browser routes with Sec-Fetch-Site=same-site fail by default",
secFetchSiteSameSite: true,
httpMethod: http.MethodPost,
apiRoute: false,
wantStatus: http.StatusForbidden,
},
{
name: "POST requests to browser routes with Sec-Fetch-Site=same-site pass if configured",
secFetchSiteSameSite: true,
permitSameSite: true,
httpMethod: http.MethodPost,
apiRoute: false,
wantStatus: http.StatusOK,
},
{
name: "POST requests to API routes do not require Sec-Fetch-Site header",
httpMethod: http.MethodPost,
apiRoute: true,
wantStatus: http.StatusOK,
},
}
for _, tt := range tests {
@ -199,7 +232,7 @@ func TestCSRFProtection(t *testing.T) {
defer s.Close()
// construct the test request
req := httptest.NewRequest("POST", "/", nil)
req := httptest.NewRequest(tt.httpMethod, "/", nil)
// send JSON for API routes, form data for browser routes
if tt.apiRoute {
@ -208,25 +241,19 @@ func TestCSRFProtection(t *testing.T) {
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)
}
if tt.permitSameSite {
s.Config.AllowSecFetchSiteSameSite = true
}
if tt.secFetchSiteNone {
req.Header.Set("Sec-Fetch-Site", "none")
} else if tt.secFetchSiteSameOrigin {
req.Header.Set("Sec-Fetch-Site", "same-origin")
} else if tt.secFetchSiteSameSite {
req.Header.Set("Sec-Fetch-Site", "same-site")
} else if tt.secFetchSiteCrossSite {
req.Header.Set("Sec-Fetch-Site", "cross-site")
}
w := httptest.NewRecorder()
s.h.Handler.ServeHTTP(w, req)
resp := w.Result()
@ -294,48 +321,6 @@ func TestContentSecurityPolicyHeader(t *testing.T) {
}
}
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)
}
defer s.Close()
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
@ -607,7 +592,7 @@ func TestStrictTransportSecurityOptions(t *testing.T) {
h.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
w.Write([]byte("ok"))
}))
s, err := NewServer(Config{BrowserMux: h, SecureContext: tt.secureContext, StrictTransportSecurityOptions: tt.options})
s, err := NewServer(Config{BrowserMux: h, ServeHSTS: tt.secureContext, StrictTransportSecurityOptions: tt.options})
if err != nil {
t.Fatal(err)
}