Merge branch 'signature_verification' of https://github.com/mediaformat/wordpress-activitypub into pr/299

activitypub.php

@@ -57,6 +57,9 @@ function init() {
 	require_once \dirname( __FILE__ ) . '/includes/rest/class-following.php';
 	Rest\Following::init();
 
+	require_once \dirname( __FILE__ ) . '/includes/rest/class-server.php';
+	\Activitypub\Rest\Server::init();
+
 	require_once \dirname( __FILE__ ) . '/includes/rest/class-webfinger.php';
 	Rest\Webfinger::init();
 

includes/class-admin.php

@@ -142,6 +142,15 @@ class Admin {
 				'default'      => array( 'post', 'pages' ),
 			)
 		);
+		\register_setting(
+			'activitypub',
+			'activitypub_use_secure_mode',
+			array(
+				'type' => 'boolean',
+				'description' => \__( 'Secure mode allows blocking servers from fetching public activities', 'activitypub' ),
+				'default' => 0,
+			)
+		);
 	}
 
 	public static function add_settings_help_tab() {

includes/class-signature.php

@@ -110,14 +110,23 @@ class Signature {
 		}
 	}
 
+	/**
+	 * Verifies the http signatures
+	 *
+	 * @param WP_REQUEST | Array $request
+	 * @return void
+	 * @author Django Doucet
+	 */
 	public static function verify_http_signature( $request ) {
 		$headers = $request->get_headers();
-		$actor = isset( json_decode( $request->get_body() )->actor ) ? json_decode( $request->get_body() )->actor : '';
-		$headers['(request-target)'][0] = strtolower( $request->get_method() ) . ' /wp-json' . $request->get_route();
 
 		if ( ! $headers ) {
-			$headers = self::default_server_headers();
+			return new \WP_Error( 'activitypub_signature', 'Request not signed', array( 'status' => 403 ) );
 		}
+
+		$actor = isset( json_decode( $request->get_body() )->actor ) ? json_decode( $request->get_body() )->actor : '';
+		$headers['(request-target)'][0] = strtolower( $request->get_method() ) . ' /' . rest_get_url_prefix() . $request->get_route();
+
 		if ( array_key_exists( 'signature', $headers ) ) {
 			$signature_block = self::parse_signature_header( $headers['signature'] );
 		} elseif ( array_key_exists( 'authorization', $headers ) ) {
@@ -125,7 +134,7 @@ class Signature {
 		}
 
 		if ( ! isset( $signature_block ) || ! $signature_block ) {
-			return false;
+			return new \WP_Error( 'activitypub_signature', 'Incompatible request signature. keyId and signature are required', array( 'status' => 403 ) );
 		}
 
 		$signed_headers = $signature_block['headers'];
@@ -135,12 +144,12 @@ class Signature {
 
 		$signed_data = self::get_signed_data( $signed_headers, $signature_block, $headers );
 		if ( ! $signed_data ) {
-			return false;
+			return new \WP_Error( 'activitypub_signature', 'Signed request date outside acceptable time window', array( 'status' => 403 ) );
 		}
 
 		$algorithm = self::get_signature_algorithm( $signature_block );
 		if ( ! $algorithm ) {
-			return false;
+			return new \WP_Error( 'activitypub_signature', 'Unsupported signature algorithm (only rsa-sha256 and hs2019 are supported)', array( 'status' => 403 ) );
 		}
 
 		if ( \in_array( 'digest', $signed_headers, true ) && isset( $body ) ) {
@@ -156,41 +165,49 @@ class Signature {
 			}
 
 			if ( \base64_encode( \hash( $hashalg, $body, true ) ) !== $digest[1] ) { // phpcs:ignore
-				return false;
+				return new \WP_Error( 'activitypub_signature', 'Invalid Digest header', array( 'status' => 403 ) );
 			}
 		}
 
-		$public_key = \rtrim( \Activitypub\get_publickey_by_actor( $actor, $signature_block['keyId'] ) ); // phpcs:ignore
-
-		return \openssl_verify( $signed_data, $signature_block['signature'], $public_key, $algorithm ) > 0;
-
-	}
-
-	public static function default_server_headers() {
-		$headers = array(
-			'(request-target)' => strtolower( $_SERVER['REQUEST_METHOD'] ) . ' ' . $_SERVER['REQUEST_URI'],
-			'content-type' => $_SERVER['CONTENT_TYPE'],
-			'content-length' => $_SERVER['CONTENT_LENGTH'],
-		);
-		foreach ( $_SERVER as $k => $v ) {
-			if ( \strpos( $k, 'HTTP_' ) === 0 ) {
-				$field = \str_replace( '_', '-', \strtolower( \substr( $k, 5 ) ) );
-				$headers[ $field ] = $v;
-			}
+		$public_key = \Activitypub\get_publickey_by_actor( $actor, $signature_block['keyId'] ); // phpcs:ignore
+		if ( \is_wp_error( $public_key ) ) {
+			return $public_key;
+		} else {
+			$public_key = \rtrim( $public_key );
 		}
-		return $headers;
+		$verified = \openssl_verify( $signed_data, $signature_block['signature'], $public_key, $algorithm ) > 0;
+		if ( ! $verified ) {
+			return new \WP_Error( 'activitypub_signature', 'Invalid signature', array( 'status' => 403 ) ); // phpcs:ignore null coalescing operator
+		}
+
 	}
 
+	/**
+	 * Gets the signature algorithm from the signature header
+	 *
+	 * @param array $signature_block
+	 * @return string algorithm
+	 * @author Django Doucet
+	 */
 	public static function get_signature_algorithm( $signature_block ) {
-		switch ( $signature_block['algorithm'] ) {
-			case 'rsa-sha-512':
-				return 'sha512';
-			default:
-				return 'sha256';
+		if ( $signature_block['algorithm'] ) {
+			switch ( $signature_block['algorithm'] ) {
+				case 'rsa-sha-512':
+					return 'sha512'; //hs2019 https://datatracker.ietf.org/doc/html/draft-cavage-http-signatures-12
+				default:
+					return 'sha256';
+			}
 		}
 		return false;
 	}
 
+	/**
+	 * Parses the Signature header
+	 *
+	 * @param array $header
+	 * @return array signature parts
+	 * @author Django Doucet <django.doucet@webdevstudios.com>
+	 */
 	public static function parse_signature_header( $header ) {
 		$ret = array();
 		$matches = array();
@@ -222,6 +239,15 @@ class Signature {
 		return $ret;
 	}
 
+	/**
+	 * Gets the header data from the included pseudo headers
+	 *
+	 * @param array $signed_headers
+	 * @param array $signature_block (pseudo-headers)
+	 * @param array $headers (original http headers)
+	 * @return signed headers for comparison
+	 * @author Django Doucet
+	 */
 	public static function get_signed_data( $signed_headers, $signature_block, $headers ) {
 		$signed_data = '';
 		// This also verifies time-based values by returning false if any of these are out of range.

includes/functions.php

@@ -219,15 +219,6 @@ function get_publickey_by_actor( $actor, $key_id ) {
 	return new \WP_Error( 'activitypub_no_public_key', \__( 'No "Public-Key" found', 'activitypub' ), $metadata );
 }
 
-function get_actor_from_key( $key_id ) {
-	$actor = \strip_fragment_from_url( $key_id );
-	if ( $actor === $key_id ) {
-		// strip /main-key/ for GoToSocial.
-		$actor = \dirname( $key_id );
-	}
-	return $actor;
-}
-
 function get_follower_inboxes( $user_id, $cc = array() ) {
 	$followers = \Activitypub\Peer\Followers::get_followers( $user_id );
 	$followers = array_merge( $followers, $cc );

includes/rest/class-inbox.php

@@ -115,6 +115,7 @@ class Inbox {
 	 * @return WP_REST_Response
 	 */
 	public static function user_inbox_post( $request ) {
+
 		$user_id = $request->get_param( 'user_id' );
 
 		$data = $request->get_params();
@@ -135,6 +136,7 @@ class Inbox {
 	 * @return WP_REST_Response
 	 */
 	public static function shared_inbox_post( $request ) {
+
 		$data = $request->get_params();
 		$type = $request->get_param( 'type' );
 		$users = self::extract_recipients( $data );
@@ -214,16 +216,6 @@ class Inbox {
 			'sanitize_callback' => 'esc_url_raw',
 		);
 
-		$params['signature'] = array(
-			'required' => true,
-			'validate_callback' => function( $param, $request, $key ) {
-				if ( ! Signature::verify_http_signature( $request ) ) {
-					return false; // returns http 400 rest_invalid_param
-				}
-				return $param;
-			},
-		);
-
 		$params['actor'] = array(
 			'required' => true,
 			'sanitize_callback' => function( $param, $request, $key ) {
@@ -266,12 +258,6 @@ class Inbox {
 			'required' => true,
 			'type' => 'string',
 			'sanitize_callback' => 'esc_url_raw',
-			'validate_callback' => function( $param, $request, $key ) {
-				if ( ! Signature::verify_http_signature( $request ) ) {
-					return false;
-				}
-				return $param;
-			},
 		);
 
 		$params['actor'] = array(

includes/rest/class-server.php

@@ -0,0 +1,55 @@
+<?php
+namespace Activitypub\Rest;
+
+use Activitypub\Signature;
+
+/**
+ * ActivityPub Server REST-Class
+ *
+ * @author Django Doucet
+ *
+ * @see https://www.w3.org/TR/activitypub/#security-verification
+ */
+class Server {
+
+	/**
+	 * Initialize the class, registering WordPress hooks
+	 */
+	public static function init() {
+		\add_filter( 'rest_request_before_callbacks', array( '\Activitypub\Rest\Server', 'authorize_activitypub_requests' ), 10, 3 );
+	}
+
+	/**
+	 * Callback function to authorize each api requests
+	 *
+	 * @see \WP_REST_Request
+	 *
+	 * @param                  $response
+	 * @param                  $handler
+	 * @param \WP_REST_Request $request
+	 *
+	 * @return mixed|\WP_Error
+	 */
+	public static function authorize_activitypub_requests( $response, $handler, $request ) {
+
+		$maybe_activitypub = $request->get_route();
+		if ( str_starts_with( $maybe_activitypub, '/activitypub' ) ) {
+			if ( 'POST' === $request->get_method() ) {
+				$verified_request = Signature::verify_http_signature( $request );
+
+				if ( \is_wp_error( $verified_request ) ) {
+					return $verified_request;
+				}
+			} else {
+				// SecureMode/Authorized fetch.
+				$secure_mode = \get_option( 'activitypub_use_secure_mode', '0' );
+
+				if ( $secure_mode ) {
+					if ( \is_wp_error( $verified_request ) ) {
+						return $verified_request;
+					}
+				}
+			}
+		}
+	}
+}

templates/settings.php

@@ -171,6 +171,21 @@
 			</tbody>
 		</table>
 
+		<table class="form-table">
+			<tbody>
+				<tr>
+					<th scope="row">
+						<?php \esc_html_e( 'Secure Mode', 'activitypub' ); ?>
+					</th>
+					<td>
+						<p>
+							<label><input type="checkbox" name="activitypub_use_secure_mode" id="activitypub_use_secure_mode" value="1" <?php echo \checked( '1', \get_option( 'activitypub_use_secure_mode', '0' ) ); ?> /> <?php echo wp_kses( \__( 'In secure mode every ActivityPub request must be signed. This disallows anonymous requests and prevents serving content to servers listed in the Blocklist.', 'activitypub' ), 'default' ); ?></label>
+						</p>
+					</td>
+				</tr>
+			</tbody>
+		</table>
+
 		<?php \do_settings_fields( 'activitypub', 'server' ); ?>
 
 		<?php \do_settings_sections( 'activitypub' ); ?>