From 11ab3d6c82a1d3a89b1024f77349fb60a83743c5 Mon Sep 17 00:00:00 2001
From: Damien Regad <dregad@mantisbt.org>
Date: Fri, 27 May 2016 11:39:58 +0200
Subject: [PATCH] Fix XSS in custom fields management

Kacper Szurek (http://security.szurek.pl/) discovered an XSS
vulnerability in Custom fields management pages, caused by unescaped
output of 'return URL' GPC parameter. His report describes two ways to
exploit this issue:

1. using 'accesskey' inside hidden input field (see [1]) reflects XSS to
   the administrator in manage_custom_field_edit_page.php when the
   keyboard shortcut is actioned
2. using 'javascript:' URI scheme executes the code when the user clicks
   the [Proceed] link on manage_custom_field_update.php after updating
   a custom field

This commit fixes both attack vectors:

- properly escape the return URL prior to printing it on the hidden form
  field
- let html_operation_successful() sanitize the URL before displaying
  it, just like html_meta_redirect() does. In this case, if the
  string contains an URI scheme, it will be replaced by 'index.php'

[1] http://blog.portswigger.net/2015/11/xss-in-hidden-input-fields.html

Fixes #20956
---
 core/html_api.php                 | 2 +-
 manage_custom_field_edit_page.php | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/core/html_api.php b/core/html_api.php
index b8a3ac3eff..55696e3a15 100644
--- a/core/html_api.php
+++ b/core/html_api.php
@@ -647,7 +647,7 @@ function html_operation_successful( $p_redirect_url, $p_message = '' ) {
 	}
 
 	echo lang_get( 'operation_successful' ).'<br />';
-	print_bracket_link( $p_redirect_url, lang_get( 'proceed' ) );
+	print_bracket_link( string_sanitize_url( $p_redirect_url ), lang_get( 'proceed' ) );
 	echo '</div>';
 }
 
diff --git a/manage_custom_field_edit_page.php b/manage_custom_field_edit_page.php
index 008d457d52..b29cfd6380 100644
--- a/manage_custom_field_edit_page.php
+++ b/manage_custom_field_edit_page.php
@@ -73,7 +73,7 @@
 			<legend><span><?php echo lang_get( 'edit_custom_field_title' ) ?></span></legend>
 			<?php echo form_security_field( 'manage_custom_field_update' ); ?>
 			<input type="hidden" name="field_id" value="<?php echo $f_field_id ?>" />
-			<input type="hidden" name="return" value="<?php echo $f_return ?>" />
+			<input type="hidden" name="return" value="<?php echo string_attribute( $f_return ); ?>" />
 			<div class="field-container">
 				<label for="custom-field-name"><span><?php echo lang_get( 'custom_field_name' ) ?></span></label>
 				<span class="input"><input type="text" id="custom-field-name" name="name" size="32" maxlength="64" value="<?php echo string_attribute( $t_definition['name'] ) ?>" /></span>