Index: includes/core/sub-actions.php
===================================================================
--- includes/core/sub-actions.php	(revision 2306827)
+++ includes/core/sub-actions.php	(working copy)
@@ -400,31 +400,31 @@ function bbp_post_request() {
 }
 
 /**
  * The main action used for handling theme-side GET requests
  *
  * @since 2.3.0 bbPress (r4550)
  */
 function bbp_get_request() {
 
 	// Bail if not a POST action
 	if ( ! bbp_is_get_request() ) {
 		return;
 	}
 
 	// Bail if no action
-	if ( empty( $_GET['action'] ) ) {
+	if ( empty( $_GET['action'] ) || ! is_string( $_GET['action'] ) ) {
 		return;
 	}
 
 	// Sanitize the GET action
 	$action = sanitize_key( $_GET['action'] );
 
 	// Bail if action was totally invalid
 	if ( empty( $action ) ) {
 		return;
 	}
 
 	// This dynamic action is probably the one you want to use. It narrows down
 	// the scope of the 'action' without needing to check it in your function.
 	do_action( 'bbp_get_request_' . $action );