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Content Security Policy; Great! or Wait?

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A couple of days ago I had another look at Content Security Policy, a technology that allows a site to tell a browser resources are allowed to be loaded to protect against XSS and some other types of web application vulnerabilities. CSP was originally devised by the Firefoxians, but is in the process of being standardized by the W3C with support in Firefox, Chrome, Safari and even the upcoming Internet Explorer 10.
Great!
The functionality offered by CSP (blocking requests that are not allowed) is pretty close to what WP DoNotTrack tries to do, so I decided I’d try to integrate CSP in my plugin, based on the following assumptions:

  • CSP-mode will only work for WP DoNotTrack if it is configured to use a whitelist
  • As most WordPress+plugins installations are bound to have pages with at least inline JavaScript and/or style, I have to add “unsafe-inline” to allow those to continue to work (which indeed limits the level of protection against XSS-attacks)
  • Given that a lot (most?) WordPress installations implement WP Super Cache of W3 Total Cache, it will -at least in a first stage- only kick in if WP  DoNotTrack is configured to filter unconditionally
  • Ideally the JavaScript-based component of WP DoNotTrack would “see” that CSP was activated and would not perform those nifty JavaScript AOP trickery

The “proof of concept”-quality code I ended up adding to wp-donottrack.php was pretty simple:

function wp_donottrack_csp() {
 global $listmode;
 if ($listmode==="1") {
  $whitelist=wp_donottrack_getWhiteList(true);
  $csp="default-src 'self' 'unsafe-inline'";
  if (is_array($whitelist)) {
   foreach ($whitelist as $white) {
    $csp.=" *.".$white;
   }
  }
  header("X-Content-Security-Policy: " . $csp); //FF & MSIE10
  header("Content-Security-Policy: ". $csp); //new standard
  header("X-WebKit-CSP: " . $csp); //chrome & safari
 }
}
add_action('init', 'wp_donottrack_csp', 10, 0);

Wait?
With this code on my testblog I started playing around in a couple of browsers. Based on that experience I found the following limitations:

So in this particular context (and specifically the absolute need for “unsafe-inline”), I’ve decided to hold off implementing CSP (I might implement iFrame sandboxing as support for that is coming with IE10 and will probably also land in Firefox 17). But if you have full control over a particular website or -application (meaning you can remove all inline JavaScript and CSS and all instances of evals in insourced JavaScript) and you want to harden your installation to stop cross-site scripting, you really should start thinking about implementing CSP (as Twitter seems to have done already)!

Browser choice, vacuming & security for father-in-laws

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Being “the computer guy” in the family might be a pain in the ass sometimes, but trying to help out users that are not tech savvy can be very revealing. Yesterday my father-in-law asked me to take a look at his computer, there was something about the browser that was not right. Turned out he let Google lure him into downloading Chrome and making it the default browser. What bothered him most about Chrome was the lack of menu’s (file|edit|…|help), while a lot of the us (the in-crowd) consider the minimal use of chrome a plus. Usability is not only about clean, simple UI’s, but also about not breaking novice users’ expectations of how your application looks and behaves.
Anyway, I showed him IE8 and Firefox 3.5 (both were installed as well) and he recognized Firefox as the browser he was most familiar with. So I uninstalled Chrome, hid IE8, upgraded him to FF 3.6 and also installed the “Vacuum Places improved” and NoScript add-ons.
“Vacuum Places improved” cleans up the places sqlite database where Firefox stores bookmarks and history and which can become very big over time.  When tweaking the options (“hide icon” and “auto-vacuum every 20 browser starts”) it was a great way to invisibly tune browser performance, but it turns out Firefox 3.6 vacuums places.sqlite automatically (when  idle, every 1 to 2 months). So Pierre, if you ever read this; remind me to uninstall “Vacuum Places improved” next time! 🙂
NoScript is a whole other beast; it is a add-on for the security-conscious tech-head, which by default disables javascript, flash, java, … It’s a great add-on, but it is very disruptive and as such totally unfit for novice users. Unless you change the configuration off course, because modifying these options makes NoScript a must-have addon for both you and your grandma;

  • General: check “Scripts Globally Allowed (dangerous)”
  • Embeddings: uncheck the 8 “Forbid” options, check both “untrusted” and “trusted” for Clearclick protection
  • Appearance: uncheck “Status bar icon”, “Status bar label” and “Contextual menu”
  • Advanced/XSS: check “Sanitize cross-site suspicious requests”

Although the first option specifically claims it is dangerous to do so, these changes render NoScript into an add-on that provides a lot of extra security (protecting against clickjacking, cross-site scripting and implementing support for x-frame-options and Strict Transport Security) without bothering users with new UI-elements containing incomprehensible questions, messages or options.
Because web security is not only about protecting against threats, but also about not breaking novice users’ expectations of how your secured browser (and the web) looks and behaves.

Browser enforced web application security; IE8 safest?

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microsoft internet explorer 8 logoWith a notoriously bad reputation for security (or the lack thereof) in Internet Explorer, Microsoft claims to have invested a lot in IE8 security in general and specifically in browser enforced website security. Indeed, according to the product site, IE8:

[…] helps protect you from today’s threats, including malware and phishing, as well as emerging threats that can compromise your computer without your knowledge. Other browsers either don’t offer you this level of protection or require you to download and configure third-party add-ons to get it, but with Internet Explorer 8 you get it right out of the box, and turned on by default.

And in August Microsoft proudly pointed to results of a (MS commissioned) study by NSSLabs, which stated that IE8 blocked 81% of malware download attempts vs. 27% for FF3 (and even less for other browsers) and 83% of phishing attacks vs. 80% for FF3 (and 54% for Opera 10 and less for Chrome and Safari).
So there you have it, IE8 is the safest browser around, no? Well, that would be jumping to conclusions; IE8 still has it’s fair share of browser security issues (but don’t they all) and the dreaded security-hole called ActiveX is still supported as well. Let’s just focus at how IE8 tries to protect you from malicious websites and compare that functionality with what the competition has to offer.

Smartscreen Filter

Smartscreen filter is the name for the Microsoft technology that uses an “in-the-cloud reputation database” which is contacted by the browser to assess the trustworthiness of a URL. Using that information, access to dangerous sites and downloads of malware can be blocked. The system is very similar to Google Safe Browsing that is implemented in Firefox, Chrome and Safari, but Smartscreen seems to be better in stopping malware from being downloaded. On the other hand the 2nd NSSlabs-study deemed both as effective when it comes to blocking access to phishing sites. Based on these (MS sponsored) results one could conclude that IE8 might have an advantage over the competition, but I for one would be very interested in an updated version of these tests with cooperation from the other browser-makers.

XSS-filter

IE8’s XSS-filter offers protection against type1 cross-site scripting attacks. Although it offers no protection against (less common) type0 and type2 xss-attacks, the mere fact that IE8 does offer out of the box XSS-protection is a big thing. Except … except apperantly there’s a serious bug in IE8’s XSS-filter, that can be abused to do cross-site scripting. Microsoft has not yet confirmed or fixed the bug,  leading some sites (e.g. Google) to disable the XSS-filter by adding “X-XSS-Protection: 0” to the http response header. Now isn’t that ironic?

Clickjacking defense

Microsoft also included clickjacking defense in IE8, by letting website owners define whether or not their pages are allowed to be included in (i)frames. This can be done by simply adding “x-frame-options” to the http response header with values “deny” to deny a page from being shown in any frame and “sameorigin” to limit framing to pages from the same domain. x-frame-options however does not protect against clickjacking with flash or other embeds.

But where’s the competition?

So what’s available in Firefox, Chrome and Safari apart from the Google Safe Browsing implementation? Nothing much up until now, I’m afraid …
At Mozilla smart guys are working on “Content security policy“. CSP is a declarative server-driven anti-XSS framework, with policies being pushed through HTTP headers. Although the policy may require non-trivial website changes because inline scripts will be disallowed by default, it certainly has potential (to the extend Microsoft is said to be interested). But CSP is not there yet, now is it?
Over at Google, engineers are including (type1) XSS-protection and support for the Strict Transport Security spec (forcing a browser to load a site only over HTTPS by issuing an http response header) in the dev-channel builds of Chrome 4. As some may have noticed while looking for Google Talk’s chatback badge last week, x-frame-options (as anti-clickjacking measure) has already been implemented in Safari4 and Chrome3 as well. So especially Google is trying to make some serious progress, but Chrome 4 can hardly be considered granny-ready, can it?
That leaves us Firefox with the NoScript extension, but I’ll come back to that combination in a minute.

IE8 the safest browser?

OK, this might hurt, but let’s give credit where credit is due; IE8 indeed seems to offer the best out of the box protection against malicious websites. It is the only browser to come with good phishing- and malware-blocking (Smartscreen) combined with (limited and currently broken) protection against some types of XSS and clickjacking-attacks. So thank you Redmond for setting the example!

The only alternative: Firefox + NoScript

Firefox does not offer the out of the box protection IE8 does, but when combined with the NoScript extension, it really is the only readily available alternative (Lynx not withstanding). NoScript offers superior protection against XSS, clickjacking and a host of other threats.
Even if you’re only vaguely security-conscious, installing Firefox and NoScript should really be your first choice. Depending on the level of protection you want, you can use the default but disruptive whitelist configuration (which blocks all javascript and flash) or switch to the less secure “Allow scripts globally” mode. But whatever configuration you choose, anti-XSS and clickjacking protection are always enabled.
It really is beyond me why NoScript’s Clearclick and anti-xss aren’t in Firefox by default, especially since they seem complementary to CSP, as they’re barely disruptive for a novice user and (last but not least) as Mozilla could easily one-up Microsoft this way? Anyone?