Merge pull request from GHSA-pmjg-52h9-72qv

Signed-off-by: Michael Crenshaw <michael@crenshaw.dev>

formatting

Signed-off-by: Michael Crenshaw <michael@crenshaw.dev>

fixes from comments

Signed-off-by: Michael Crenshaw <michael@crenshaw.dev>

fix test

Signed-off-by: Michael Crenshaw <michael@crenshaw.dev>

util/oidc/oidc.go

@@ -28,6 +28,8 @@ import (
 	"github.com/argoproj/argo-cd/v2/util/settings"
 )
 
+var InvalidRedirectURLError = fmt.Errorf("invalid return URL")
+
 const (
 	GrantTypeAuthorizationCode = "authorization_code"
 	GrantTypeImplicit          = "implicit"
@@ -185,10 +187,18 @@ func (a *ClientApp) verifyAppState(r *http.Request, w http.ResponseWriter, state
 		return "", err
 	}
 	cookieVal := string(val)
-	returnURL := a.baseHRef
+	redirectURL := a.baseHRef
 	parts := strings.SplitN(cookieVal, ":", 2)
 	if len(parts) == 2 && parts[1] != "" {
-		returnURL = parts[1]
+		if !isValidRedirectURL(parts[1], []string{a.settings.URL}) {
+			sanitizedUrl := parts[1]
+			if len(sanitizedUrl) > 100 {
+				sanitizedUrl = sanitizedUrl[:100]
+			}
+			log.Warnf("Failed to verify app state - got invalid redirectURL %q", sanitizedUrl)
+			return "", fmt.Errorf("failed to verify app state: %w", InvalidRedirectURLError)
+		}
+		redirectURL = parts[1]
 	}
 	if parts[0] != state {
 		return "", fmt.Errorf("invalid state in '%s' cookie", common.AuthCookieName)
@@ -201,7 +211,7 @@ func (a *ClientApp) verifyAppState(r *http.Request, w http.ResponseWriter, state
 		SameSite: http.SameSiteLaxMode,
 		Secure:   a.secureCookie,
 	})
-	return returnURL, nil
+	return redirectURL, nil
 }
 
 // isValidRedirectURL checks whether the given redirectURL matches on of the

util/oidc/oidc_test.go

@@ -191,7 +191,7 @@ func TestGenerateAppState(t *testing.T) {
 	signature, err := util.MakeSignature(32)
 	require.NoError(t, err)
 	expectedReturnURL := "http://argocd.example.com/"
-	app, err := NewClientApp(&settings.ArgoCDSettings{ServerSignature: signature}, "", "")
+	app, err := NewClientApp(&settings.ArgoCDSettings{ServerSignature: signature, URL: expectedReturnURL}, "", "")
 	require.NoError(t, err)
 	generateResponse := httptest.NewRecorder()
 	state, err := app.generateAppState(expectedReturnURL, generateResponse)
@@ -219,6 +219,56 @@ func TestGenerateAppState(t *testing.T) {
 	})
 }
 
+func TestGenerateAppState_XSS(t *testing.T) {
+	signature, err := util.MakeSignature(32)
+	require.NoError(t, err)
+	app, err := NewClientApp(
+		&settings.ArgoCDSettings{
+			// Only return URLs starting with this base should be allowed.
+			URL: "https://argocd.example.com",
+			ServerSignature: signature,
+		},
+		"", "",
+	)
+	require.NoError(t, err)
+
+	t.Run("XSS fails", func(t *testing.T) {
+		// This attack assumes the attacker has compromised the server's secret key. We use `generateAppState` here for
+		// convenience, but an attacker with access to the server secret could write their own code to generate the
+		// malicious cookie.
+
+		expectedReturnURL := "javascript: alert('hi')"
+		generateResponse := httptest.NewRecorder()
+		state, err := app.generateAppState(expectedReturnURL, generateResponse)
+		require.NoError(t, err)
+
+		req := httptest.NewRequest("GET", "/", nil)
+		for _, cookie := range generateResponse.Result().Cookies() {
+			req.AddCookie(cookie)
+		}
+
+		returnURL, err := app.verifyAppState(req, httptest.NewRecorder(), state)
+		assert.ErrorIs(t, err, InvalidRedirectURLError)
+		assert.Empty(t, returnURL)
+	})
+
+	t.Run("valid return URL succeeds", func(t *testing.T) {
+		expectedReturnURL := "https://argocd.example.com/some/path"
+		generateResponse := httptest.NewRecorder()
+		state, err := app.generateAppState(expectedReturnURL, generateResponse)
+		require.NoError(t, err)
+
+		req := httptest.NewRequest("GET", "/", nil)
+		for _, cookie := range generateResponse.Result().Cookies() {
+			req.AddCookie(cookie)
+		}
+
+		returnURL, err := app.verifyAppState(req, httptest.NewRecorder(), state)
+		assert.NoError(t, err, InvalidRedirectURLError)
+		assert.Equal(t, expectedReturnURL, returnURL)
+	})
+}
+
 func TestGenerateAppState_NoReturnURL(t *testing.T) {
 	signature, err := util.MakeSignature(32)
 	require.NoError(t, err)