hackademix.net

So I just come back from my honeymoon journey (Greece, Turkey and Croatia) right in time to find that Sirdarckcat and Kuza55 teamed together to throw a friendly defacement at our beloved RSnake!

The kids miserably failed, nevertheless RSnake did not like it a bit.
Their payload was playful rather than venomous in my opinion, but you can judge by yourself:

0wning RSnake For Fun and PageRank

So, you’re sitting on the sla.ckers.org irc channel one day and someone is poking around with one of RSnake’s tools, and finds that its not working, or at least that’s what it seems like untill they realise that its not just broken, its broken in a fun XSS way :) - what do you do? Do you: a) Urge the person to report the problem to the vendor (RSnake), and get mad props for being awesome? b) Scream about how the vendor is a security “expert” and needs to “secure their shit!!!1111″? c) 0wn the vendor for Fun and PageRank Well, to me, the answer seemed fairly obvious. Since the “Evil Advertising Empire” (Google), cue ominous music….now, had done a little dance and increased the PageRank of our blogs, we had gotten a taste of the power which we could amass, muahahaha, and we wanted more! Or at least I did….. So anyway, Hey RSnake :) Thanks for the free advertising space. Anyway, credit goes to: sirdarckcat for not only being generally awesome, but finding the actual exploit. thornmaker for (inadvertently) providing us with a method to get our payload through NoScript (Javascript variable setter’s and window.name FTW!), so umm, hey thornmaker :) Gareth Heyes for doing that awesome research on selective payloads using CSS, which where implemened in the exploit. kuza55 for not really doing anything, but being in the right place at the right time but being able to get some free Googlejuice from things anyway :p Oh, and, of course: XSS! We now return you to your regularly unscheduled posting ;) - kuza55 & sirdarckcat P.S. Thanks for directing carja.ckers.org to 127.0.0.1 :) P.S.2. Sorry .mario, NoScript is the new attack playground :P, we’ll be back to php-ids ASAP.

At any rate, from my NoScript standpoint, nice setter+name bypass combo — just you send me a mail next time, thanks ;)
Latest release already defeats it, but for those who disabled automatic updates, it’s time to get it…

If the GoogHOle wasn’t wide enough, yesterday Petko D. Petkov AKA pdp posted another “semi-disclosure” about how you can redirect someone else’s GMail incoming messages to your account.
Petko declared “I am not planning to release this vulnerability for now”, but this counts as a full disclosure in my book, since the details he gives away are far more than enough to put up a proof of concept in 10 minutes, if the reader knowns the very basics of Cross Site Request Forgery (CSRF).

1. Victim must be logged in GMail.
2. Victim must visit a malicious web page: most likely scenarios are clicking an external link from an incoming message or surfing porn while checking email from time to time.
3. The malicious web site forges a POST request to GMail’s “Create Filter” wizard, possibly using an autosubmit invisible form to build a filter which forwards incoming messages to a mail recipient owned by the attacker.
4. Since user is already authenticated, her session cookie is passed along with the forged request and the GMail filter gets silently implanted, with all the output hidden inside an IFRAME.
5. The new GMail filter now acts as a persistent backdoor stealing incoming messages, and it will go unnoticed forever unless the victim is a power GMail user who creates or edits from time to time her own filters, which are deep buried in the “Settings” user interface: I, for instance, never saw them until yesterday!

Very clever and very dangerous.
As I said, this surely counts as a 0day public full disclosure: no matter if pdp omitted an explicit PoC. How many of us, having minimal web coding experience, wouldn’t be able to build a working exploit using the info above?

CSRF Countermeasures

As usual, now that’s been publicly disclosed, this vulnerability is being patched very quickly by the great Google development crew.
Nonetheless, many other holes of this kind are still around. That’s why CSRF is called “The Sleeping Giant”: some web coders may still need to learn how to fix or prevent them, and users surely want to know how to protect themselves.

1. Web Developers

Please use form keys!

1. Generate a random identifier (form key) every time you display a form meant to be submitted by authenticated users only.
2. Echo your key as an hidden field of the form and bind its value to the user session data kept on the server side.
3. As soon the form is submitted, compare the returned key with the one stored in session data: if they don’t match, throw away the request because it is probably forged.

The above is a simple yet effective anti-CSRF technique. It will work fine unless a further Cross Site Scripting (XSS) vulnerability is present too, allowing attacker to read your form key on the fly and forge a seemingly valid requests.

2. Web Users

This GMail incident proves how even the best trained web developer in the world can fail at implementing CSRF countermeasures.
Most of the existing literature about XSS and CSRF will tell you that poor users can do nothing to protect themselves from these attacks, but this is blatantly false.
A quite radical, not very usable but effective approach would be using different browsers (or different profiles, if you use Mozilla derivatives) for each “sensitive” web site you access, and force yourself not to follow any external link nor browse any other site while logged in.

Anyway, if you prefer not to make your life miserable by spawning multiple browsers and scanning every single link with a magnifying lens, your answer is, once again, Firefox + NoScript (sorry to sound repetitive, but that’s it).

First of all, automating a POST request is trivial if JavaScript is enabled on the attacker site — form.submit() — but just impossible if malicious scripts are blocked by NoScript.
The obvious objection, raised for instance by both pdp and Adrian Pastor at GNUCITIZEN, sounds like:

The attacker could simply build an invisible POST form and disguise its “submit” button as a regular link or an image, then social-engineer his victim into clicking it and so have the exploit launched no matter if JavaScript is disabled.

True, but NoScript effectively defeats this attack as well!

A common misconception about NoScript is that it just blocks JavaScript on untrusted sites.
It certainly does, but NoScript actually enhances browser security in several other ways.
A very incomplete list:

1. It blocks Java, Flash, Silverlight and other plugins on untrusted sites, and optionally also on trusted pages, while letting you activate the plugin content on demand, with a click.
2. It prevents malformed URIs to exploit buggy URI handlers, i.e. the foundation for many cross-application exploits discovered by Billy Rios, Nate McFeters and Thor Larholm.
3. It implements the most advanced and effective anti-XSS protection available on the client side.

NoScript’s anti-XSS protection deploys various specific countermeasures, e.g. HTML/JavaScript injection detection, URL sanitization on suspicious cross-site requests, UTF-7 encoding neutralization and many others.
One of them also provides an effective defense from CSRFs of the kind affecting GMail: in facts, NoScript intercepts POST requests sent from untrusted origins to trusted sites and strips out their payloads.
This means that, even if the attacker exploits a scriptless vector to launch his POST CSRF through social engineering, NoScript users are still safe as long as the malicious site is not explicitly whitelisted.

When he learned this, pdp commented:

Giorgio, sounds good, but doesn’t that break things?
I mean, CSRF is one of the most fundamental Web characteristic.
Disabling it might be OK for people like us, but for the general population, that is a no go!

Petko, my friend,

1. The very foundation of the Web is CSR (Cross Site Requests, AKA Hyperlinking), not CSRF (Cross Site Request Forgery) which is an unwanted side effect of bad coding practices.
2. RFC 2616 defining HTTP (hence, in a certain sense, the Web itself), clearly states that while GET requests (the ones we generate by following hyperlinks or submitting a search form) are idempotent, i.e. should not modify the receiving system, POST is reserved to requests which cause a permanent change. NoScript just prevents untrusted sites from modifying data held by trusted sites, and this looks Pure Good™: why could you want the contrary?
3. Even if you actually wanted the contrary, you can either use the “Unsafe reload” command, available whenever a request is filtered by NoScript, or permanently configure some sites of your choice as unfiltered recipients of unsafe requests by listing them in NoScript Options/Advanced/XSS/Exceptions

The NoScript feature we’re talking about has been in place for more than six month now.
I guess it’s transparent enough if security researchers like you, Adrian or .mario — people “like us”, much more attentive to what happens inside their browsers than “the general population” — did not even notice it… ;)

Not a great month for Google security.
In the past 3 days, 34 interesting disclosures have been published:

1. Google Search Appliance XSS discovered by MustLive, affecting almost 200,000 paying customers of the outsourced search engine and their users: this Google dork shown 196,000 results at the time of disclosure, now dropped to 188,000. Fear effect?
2. Billy Rios and Nate McFeters revealed the gory details of their already announced Picasa exploit, leveraging a clever combo of XSS, Cross Application Request Forgery, Flash same domain policy elusion and URI handler weakness exploitation to steal your private pictures, straight from your local hard disk, just visiting a malicious web page.
3. Finally, the most simple yet impressive, because of the huge number of users involved: beford decided to launch his new blog disclosing a Google Polls XSS which, thanks to the (too) smart “widget reuse” allowing Google services to integrate the same functionality across multiple services, can be used to attack Search, Blogspot, Groups and, the most dramatic exploitation scenario, GMail:
   • This POC steals your Google contacts
   • This POC steals your GMail incoming messages, routing them to beford’s mail address — not a GMail account, obviously… :P

   For such an attack to be successful, the victim just needs to visit a malicious website while logged in Google, e.g. by following a link from an incoming message (unless she’s got anti-XSS protection).

4. update — a few hours after I released the first version of article, I heard of another Google-outsourced vulnerability, an Urchin Login XSS disclosed by GNUCITIZEN’s Adrian Pastor, which could compromise local Google Analytics installations. Its severity may vary depending on how Urchin is installed (e.g. on a domain different than your main site), but the provided proof of concept is quite interesting because it shows an actual credential theft in action, rather than the usual, boring alert('XSS'). Not that a more spectacular example proves anything new about the dangers of XSS, but some people just don’t believe until they can see with their own eyes.

These vulnerabilities are surely being fixed at top speed, since Google is one of the most reactive organizations in this fight, but they’re nonetheless disturbing because they hit the very main player on the field, with the largest user base on the web: this make this kind of incidents unavoidable ipso facto.
How many vulnerabilities like those just go undisclosed and unpatched, but yet exploited by unethical hacrackers?
In Gareth Heyes‘ words,

This proves everything is insecure, there are just degrees of insecurity.

Talking about XSS, if you’re an end user and you don’t like to stay at the very bottom of the insecurity food chain, you’d better use Firefox with NoScript — but that’s your choice, of course. ;)

I’ve just read on RSnake’s blog that MustLive, a very active the Ukrainian researcher, disclosed yet another XSS vulnerability affecting the Google Search Appliance.

The Google Search Appliance starts at $30,000, whereas the Mini starts at $1,995.

This means that about 196.000 web sites, many of them belonging to very important Universities and other public bodies, are willing to pay for putting their data and their users at risk.

Last time I checked, putting up a self-hosted search engine was not a terribly hard task, no matter if you prefer Java, PHP or just plain CGI.
When you discover your own web site is broken, do you really want to depend on someone else for a fix?

GNUCITIZEN’s Petko D. Petkov (AKA pdp) just posted an interesting 0DAY disclosure about a Quicktime bug allowing JavaScript chrome privilege escalation on Gecko-based browsers — in other words, a full fledged remote arbitrary code execution vulnerability.

If you run one of those demos on Microsoft Windows, you’ll see pretty things happening, like calc.exe being launched behind your back.
Both Petko and I said this vulnerability is theoretically cross-platform, but as many reported it couldn’t actually be reproduced on Mac OS X.
It doesn’t come as a real surprise, though, since this is just another cross-application URI dispatching bug, and the Apple OS has already shown to manage this issue in a much saner way than its counterpart from Redmond.
At any rate, on Windows at least, this can be exploited to do anything the currently logged user can.
Scary, right?

However, thanks to Billy Rios, Thor Larholm and other “URI handler gangsters”, NoScript users are protected from this and similar possible exploits since 22-Jun-2007.

Even if gnucitizen.org is in your whitelist, nothing bad will happen thanks to the specific top-level chrome protection implemented almost 3 months ago.

Hmm… alert(Math.round((new Date(2007, 5, 22) - new Date(2007, 8, 12)) / 3600 / 24 / 1000)) ==> -82 ;)