So you think AJAX and Web 2.0 are all that and a bag of chips


You know, I would feel a lot better about this technology if someone had fixed basic problems with the way browsers handle JavaScript, about JavaScript policy specifications and compliance testing, and if there were good, usable and mature static analysis tools that could detect cross-site scripting vulnerabilities (Pixy by Jovanovic et al. comes to mind as a promising open source tool), and if people used them.  These problems have been known for a long time.

  1. Same origin policy and shared servers.  So, my home page is;  if I put a nasty javascript there, it can access or change the contents of other CERIAS home pages if you follow a link from my page, or if my page opens another home page for you.  I made a demo which for Safari users displays Adam Hammer’s home page url but with contents of my choosing (with apologies to Adam).  Firefox is a bit smarter and the url displayed is instead that of my page, which could clue attentive users to the fact that the content really comes from elsewhere.  Adam doesn’t actually have a home page there.
  2. Modern browsers still can’t survive a visit to this site (WARNING!  Your browser will likely crash or become unusable when you click buttons on that site):  Nasty Javascript Bombs (I didn’t try all browsers, like Opera, but Safari died horrible deaths)
  3. Modern browsers can still be captured:  Firefox users visit (WARNING!  you won’t be able to return) the jail, do not collect $200.
  4. Searching for JavaScript-related vulnerabilities in 2006 in the National Vulnerability Database gives 124 matches (and the year is not even over).  3 of those are accidental hits (because “javascript” was part of a file name or such).  About 50% are cross-site scripting vulnerabilities, that could include the above Javascript (and likely worse code than changing your choice of hero). About 40% are coding errors in the JavaScript implementation.  About 10% are still issues with the enforcement of JavaScript default security policies, or things that should explicitly be stated as part of default policies (e.g, CVE-2006-2900 and CVE-2006-2894, abusing Javascript keystroke events to trick users into typing where they didn’t mean to).  Cross-site scripting vulnerabilities are hard to avoid because scripts can be embedded almost anywhere inside HTML.  The separation between code (JavaScript) and data (HTML) is flimsy and complex.  I predict that XSS vulnerabilities will be to AJAX applications what buffer overflows and format string vulnerabilities are to C:  a real pain.  There is no sign that browsers have matured enough yet to be trusted in handling JavaScript safely, and this will likely continue for many years.
  5. Perfectly compliant JavaScript and browsers can be used to scan internal networks and even perform limited exploits.
  6. JavaScript seems to be used most of the time to perform tasks that are user-unfriendly (hide user interface elements and generally remove control from the user, create pop-unders, show ads, track you by history, etc…).  So, I should expose myself to these, and the above and future vulnerabilities, so you can program something that’s a little slicker, or poorly duplicates the functionality of executables on my system?  Huh.

So, tell me again;  do you really want to build castles on that foundation?  It sounds like a bad idea to me.  We can always hope that eventually, AJAX horror stories (to come) will drive security improvements, but I’d rather not be in the crowd of early sufferers.  At least, please do me a favor and honor the principle of graceful degradation, so that if I visit your web site with JavaScript turned off, I can still make some use of it.


Posted by Sean at Prompt
on Thursday, September 21, 2006 at 04:46 AM

Yes, there are security problems with browsers, but there are security problems with images too. I’m not convinced we want to return to the days of text only on the web.

Javascript can play an important role in making websites more useable by avoiding the need to refresh the whole page each time a detail changes. It’s been used well in some web 2 sites like gmail, digg and tadalist to give a more involving and fluid user experience. Javascript that hides useful content is down to bad design - it’s not an inherent feature of Javascript.

Javascript now is probably where Flash was a few years back - people hated the technology because of the ways that many people (ab)used it. Flash has gone on to great things and AJAX will do the same in time.

Security needs addressing urgently, and not using Javascript will reduce your vulnerability. But you risk losing many worthwhile online experiences (a definite event) out of fear of a possible attack.

Posted by Pascal Meunier
on Thursday, September 21, 2006 at 05:20 AM

I’m not getting your point about images;  nevertheless I agree with the rest of what you say.  However, as long as the fundamental issues are not addressed, AJAX applications will remain unworthy of serious business (at least for risk-conscious people).

Posted by pdp
on Thursday, September 21, 2006 at 09:04 PM

nice stuff,
here are some more examples

Posted by Watching Tech TV
on Saturday, November 11, 2006 at 07:29 AM

great article, i agree that browser companies are not doing anything to fix these problems

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