feat: add origin check for CSRF protection

.changeset/fair-jars-behave.md

@@ -0,0 +1,24 @@
+---
+"astro": minor
+---
+
+Adds a new experimental security option to prevent [Cross-Site Request Forgery (CSRF) attacks](https://owasp.org/www-community/attacks/csrf). This feature is available only for pages rendered on demand:
+
+```js
+import { defineConfig } from "astro/config"
+export default defineConfig({
+  experimental: {
+    security: {
+      csrfProtection: {
+        origin: true
+      }
+    }
+  }
+})
+```
+
+Enabling this setting performs a check that the "origin" header, automatically passed by all modern browsers, matches the URL sent by each `Request`.
+
+This experimental "origin" check is executed only for pages rendered on demand, and only for the requests `POST, `PATCH`, `DELETE` and `PUT` with one of the following `content-type` headers: 'application/x-www-form-urlencoded', 'multipart/form-data', 'text/plain'.
+
+It the "origin" header doesn't match the pathname of the request, Astro will return a 403 status code and won't render the page.

packages/astro/src/@types/astro.ts

@@ -1821,6 +1821,62 @@ export interface AstroUserConfig {
 		 * See the [Internationalization Guide](https://docs.astro.build/en/guides/internationalization/#domains-experimental) for more details, including the limitations of this experimental feature.
 		 */
 		i18nDomains?: boolean;
+
+		/**
+		 * @docs
+		 * @name experimental.security
+		 * @type {boolean}
+		 * @default `false`
+		 * @version 4.6.0
+		 * @description
+		 *
+		 * Enables CSRF protection for Astro websites.
+		 *
+		 * The CSRF protection works only for pages rendered on demand (SSR) using `server` or `hybrid` mode. The pages must opt out of prerendering in `hybrid` mode.
+		 *
+		 * ```js
+		 * // astro.config.mjs
+		 * export default defineConfig({
+		 *   output: "server",
+		 *   experimental: {
+		 *     security: {
+		 *       csrfProtection: {
+		 *         origin: true
+		 *       }
+		 *     }
+		 *   }
+		 * })
+		 * ```
+		 */
+		security?: {
+			/**
+			 * @name security.csrfProtection
+			 * @type {object}
+			 * @default '{}'
+			 * @version 4.6.0
+			 * @description
+			 *
+			 * Allows you to enable security measures to prevent CSRF attacks: https://owasp.org/www-community/attacks/csrf
+			 */
+
+			csrfProtection?: {
+				/**
+				 * @name security.csrfProtection.origin
+				 * @type {boolean}
+				 * @default 'false'
+				 * @version 4.6.0
+				 * @description
+				 *
+				 * When enabled, performs a check that the "origin" header, automatically passed by all modern browsers, matches the URL sent by each `Request`.
+				 *
+				 * The "origin" check is executed only for pages rendered on demand, and only for the requests `POST, `PATCH`, `DELETE` and `PUT` with
+				 * the following `content-type` header: 'application/x-www-form-urlencoded', 'multipart/form-data', 'text/plain'.
+				 *
+				 * If the "origin" header doesn't match the `pathname` of the request, Astro will return a 403 status code and will not render the page.
+				 */
+				origin?: boolean;
+			};
+		};
 	};
 }
 

packages/astro/src/core/app/index.ts

@@ -31,6 +31,8 @@ import { createAssetLink } from '../render/ssr-element.js';
 import { ensure404Route } from '../routing/astro-designed-error-pages.js';
 import { matchRoute } from '../routing/match.js';
 import { AppPipeline } from './pipeline.js';
+import { sequence } from '../middleware/index.js';
+import { createOriginCheckMiddleware } from './middlewares.js';
 export { deserializeManifest } from './common.js';
 
 export interface RenderOptions {
@@ -112,6 +114,13 @@ export class App {
 	 * @private
 	 */
 	#createPipeline(streaming = false) {
+		if (this.#manifest.checkOrigin) {
+			this.#manifest.middleware = sequence(
+				createOriginCheckMiddleware(),
+				this.#manifest.middleware
+			);
+		}
+
 		return AppPipeline.create({
 			logger: this.#logger,
 			manifest: this.#manifest,

packages/astro/src/core/app/middlewares.ts

@@ -0,0 +1,42 @@
+import type { MiddlewareHandler } from '../../@types/astro.js';
+import { defineMiddleware } from '../middleware/index.js';
+
+/**
+ * Content types that can be passed when sending a request via a form
+ *
+ * https://developer.mozilla.org/en-US/docs/Web/API/HTMLFormElement/enctype
+ * @private
+ */
+const FORM_CONTENT_TYPES = [
+	'application/x-www-form-urlencoded',
+	'multipart/form-data',
+	'text/plain',
+];
+
+/**
+ * Returns a middleware function in charge to check the `origin` header.
+ *
+ * @private
+ */
+export function createOriginCheckMiddleware(): MiddlewareHandler {
+	return defineMiddleware((context, next) => {
+		const { request, url } = context;
+		const contentType = request.headers.get('content-type');
+		if (contentType) {
+			if (FORM_CONTENT_TYPES.includes(contentType.toLowerCase())) {
+				const forbidden =
+					(request.method === 'POST' ||
+						request.method === 'PUT' ||
+						request.method === 'PATCH' ||
+						request.method === 'DELETE') &&
+					request.headers.get('origin') !== url.origin;
+				if (forbidden) {
+					return new Response(`Cross-site ${request.method} form submissions are forbidden`, {
+						status: 403,
+					});
+				}
+			}
+		}
+		return next();
+	});
+}

packages/astro/src/core/app/types.ts

@@ -64,6 +64,7 @@ export type SSRManifest = {
 	pageMap?: Map<ComponentPath, ImportComponentInstance>;
 	i18n: SSRManifestI18n | undefined;
 	middleware: MiddlewareHandler;
+	checkOrigin: boolean;
 };
 
 export type SSRManifestI18n = {

packages/astro/src/core/build/generate.ts

@@ -615,5 +615,6 @@ function createBuildManifest(
 		i18n: i18nManifest,
 		buildFormat: settings.config.build.format,
 		middleware,
+		checkOrigin: settings.config.experimental.security?.csrfProtection?.origin ?? false,
 	};
 }

packages/astro/src/core/build/plugins/plugin-manifest.ts

@@ -276,5 +276,6 @@ function buildManifest(
 		assets: staticFiles.map(prefixAssetPath),
 		i18n: i18nManifest,
 		buildFormat: settings.config.build.format,
+		checkOrigin: settings.config.experimental.security?.csrfProtection?.origin ?? false,
 	};
 }

packages/astro/src/core/config/schema.ts

@@ -86,6 +86,7 @@ const ASTRO_CONFIG_DEFAULTS = {
 		clientPrerender: false,
 		globalRoutePriority: false,
 		i18nDomains: false,
+		security: {},
 	},
 } satisfies AstroUserConfig & { server: { open: boolean } };
 
@@ -508,6 +509,17 @@ export const AstroConfigSchema = z.object({
 				.boolean()
 				.optional()
 				.default(ASTRO_CONFIG_DEFAULTS.experimental.globalRoutePriority),
+			security: z
+				.object({
+					csrfProtection: z
+						.object({
+							origin: z.boolean().default(false),
+						})
+						.optional()
+						.default({}),
+				})
+				.optional()
+				.default(ASTRO_CONFIG_DEFAULTS.experimental.security),
 			i18nDomains: z.boolean().optional().default(ASTRO_CONFIG_DEFAULTS.experimental.i18nDomains),
 		})
 		.strict(

packages/astro/src/vite-plugin-astro-server/plugin.ts

@@ -143,6 +143,7 @@ export function createDevelopmentManifest(settings: AstroSettings): SSRManifest
 		componentMetadata: new Map(),
 		inlinedScripts: new Map(),
 		i18n: i18nManifest,
+		checkOrigin: settings.config.experimental.security?.csrfProtection?.origin ?? false,
 		middleware(_, next) {
 			return next();
 		},