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HTML Formatter Exploit

NickENickE New
edited May 2006 in Vanilla 1.0 Help
Just as an example. The code used is
<img src="blabla.png" onerror="alert('Hello There');" width=0 height=0>
Looking through the HTML Formatter's code, I noticed it didn't replace a lot of the possible events one could hide javascript in. I'd recommend replacing all on* attributes in each tag with html entities, or just removing them all together.



  • *strokes sirnots bug finding abilities and watches him take down the forum. p.s. this is the 1000th visible discussion :D
  • NickENickE New
    edited October 2005
    I'm not just brilliant with regular expressions, but replacing all of the on* string eregi_replace() functions with the following worked for me:
    $String = preg_replace("#<(.*) on(.*)=(.*)>#si", "<\\1 &#111;n\\2=\\3>", $String);
  • lechlech Chicagoland
    lol, nice find.
  • MarkMark Vanilla Staff
    Wow - thanks, Sirnot :)
  • NickENickE New
    edited October 2005
    Sorry guys, just realized the first solution I posted dosn't work properly if there's one, no space in between on* and first attribute and/or two, there's more than on on* attribute. I think this one solves it, but like I said, I'm horrid with regular expressions. If anyone else is any good at this stuff, your help would be much appriciated.
    $String = preg_replace(array("<(.*?)on(.*?)>", "<(.*?)On(.*?)>"), array("\\1&#111;n\\2", "\\1&#76;n\\2"), $String);
    Whoops, that replaces all 'o's now. Hmm... this is getting annoying.
  • NickENickE New
    edited October 2005
    Ok, I think I actually got it this time. This should fix all js events as well as the multitudes of different ways one might get javascript to run. You want to replace your Execute() function within the HTML formatter class with the following (I didn't put in anything to replace newlines, but if you want it to just pop in an nl2br() function around the preg_replace()).
    function Execute($String)
    	$AllowedProtocols = array('http', 'ftp', 'https', 'irc', 'gopher');
    	$Patterns = array(
    		"/o(?i)(n)/", //block all js events, but keep it as exact as possible in case 
    		"/O(?i)(n)/", //we're mistaking it for a url or something
    			//on some browsers the js protocol will still work even if it
    			//contains html entities or a newline seperating 'java' and 'script'
    		"/s(?i)(cript)/", //now we can go through and cancel out any script tags
    	$Replacements = array(
    		'$this->CheckProtocol("\\3", $AllowedProtocols, "href="."\\2", "<a"."\\1", "\\4".">")', 
    	return preg_replace($Patterns, $Replacements, $String);
    Then you'd want to add in this function in the same class as well:
    function CheckProtocol($Check, $Allow, $Extra, $Prefix, $Suffix)
    	$sReturn = stripslashes($Prefix);
    	if(!in_array($Check, $Allow)) $sReturn .= ($Extra.'http://');
    	else $sReturn .= ($Extra.$Check.':');
    	$sReturn .= stripslashes($Suffix);
    	return $sReturn;
    lol, just as I thought; the current HTML parser dosn't fix the fact that most browsers'll still parse the js protocol even if it has entities in it:
    Click Me
    So that's three bugs discovered so far, hopefully all fixed in this revision.
  • MarkMark Vanilla Staff
    It's up here now. It did some strange stuff to your post there. I'll test a bit.
  • MarkMark Vanilla Staff
    Okay - better. Thanks!
  • Is version 1.2 Of HTMLFormatter (the one included with Vanilla 0.9.3) the most recent version of the extension? Not sure wether to make these changes to HTML Formatter 1.2, looks like the info right here on the message boards is out of date.
  • also, are you posting these fixes to the addons directory?
  • MarkMark Vanilla Staff
    I'd bet dollars to donuts that this is out of date. Look at the date it was posted: Oct 26th, 2005
  • oh jeez.

    no wonder it didn't work :)

    *gives mark donuts
  • edited April 2006
    hehe. i was inspired
  • Yeah, I assumed it was out of the date for that very reason. No date is in the extension itself though.
  • MarkMark Vanilla Staff
    SirNot has been maintaining this extension for quite a while now. I've asked him to upload it to the add-on directory so updates can be seen.
  • Sir Not, is this extension ready for the add-on directory?
This discussion has been closed.