Index: filter.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/filter/filter.module,v
retrieving revision 1.152
diff -u -r1.152 filter.module
--- filter.module	26 Nov 2006 23:01:42 -0000	1.152
+++ filter.module	12 Feb 2007 17:36:58 -0000
@@ -1455,7 +1455,8 @@
     $before = $string;
     $colonpos = strpos($string, ':');
     if ($colonpos > 0) {
-      $protocol = substr($string, 0, $colonpos);
+      // Per RFC2616, section 3.2.3 (URI Comparison) scheme comparison must be case-insensitive
+      $protocol = strtolower(substr($string, 0, $colonpos));
       if (!isset($allowed_protocols[$protocol])) {
         $string = substr($string, $colonpos + 1);
       }