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DNS Testing Image

As we are all trying to patch and upgrade our resolvers and NAT devices, I created a small image tag that automatically assesses the randomess of a visitor's resolver:

This is still in reference to the CERT Advisory on Multiple DNS implementations vulnerable to cache poisoning. You can place the image tag on your web page to test your visitors:
<center><a href=""><img src="" border=0></a></center>

The a href link can of course point to a more helpful web page and the image itself can also be changed according to need.

If you want to show this on your pages with different images, just let me know.

Categories: Hacking, Security
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DNS and Randomness

Over the last few days, we have heard a lot about DNS cache poisoning and how we need to get our recursive resolvers to use random source ports. We are being told that this is a flaw in the protocol, but no details are going to be available until a presentation at Blackhat in August. DNS cache poisoning of course has been around for a long time, most notably when the 16-bit query IDs were not randomized. Here are some good references:
Oarc in the meantime has made a port testing server available. A simple invocation of dig tells you if your recursive resolver is vulnerable:
dig +short TXT

The TXT record assesses a resolver's source port randomness as poor, fair or good. Unfortunately, on my network, I found this record constantly cached from other resolvers, so I wrote a small Python tool that analyzes the randomness of both your source port numbers as a well as your query IDs. The tool can be downloaded from:

Its usage is pretty simple:
Continue reading "DNS and Randomness"
Categories: Hacking
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HotSec is Hot!

This year, I have the pleasure of chairing the 3rd USENIX Workshop on Hot Topics in Security, an invitation-only workshop that provides a forum for leading security researchers to discuss current trends and new research ideas. At the program committee meeting in Mountain View, we selected 13 out of 37 papers for the final program. It's pretty hot. Here are some of the talks I am looking forward to:

  • Towards Application Security on Untrusted Operating Systems
  • Defeating Deniable File Systems: A TrueCrypt Case Study
  • Panic Passwords: Authenticating under Duress
  • Absence Makes the Heart Grow Fonder: New Directions for Implantable Medical Device Security

HotSec is taking place on July 29th, one day before the technical program of the USENIX Security Symposium. The keynote for USENIX Security is going to be exciting: Debra Bowen, the California Secretary of State, is speaking on Dr. Strangevote or: How I Learned to Stop Worrying and Love the Paper Ballot.

See you there,
Categories: News
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Anonymity, Tor and Your Browser

I often use Tor for anonymous web browsing; mostly when investigating malware distribution sites. Most people configure their browser so that it proxies HTTP via Privoxy to the Tor network. At that point, Tor is doing your DNS resolutions and also hides your TCP connections from preying eyes. Or at least, so one would think. There are many ways in which an adversary can trivially circumvent this setup. For example, if we configure the browser to proxy only HTTP, a malicious web page can easily open an HTTPS connection and reveal your IP address. Things get much worse when scripting languages such as Javascript, Flash or Java come into play. Flash can open raw sockets and learn a lot about your local environment.

To prevent information leakage, we ideally would run a virtual machine that tunnels all traffic via Tor, such as the VirtualPrivacyMachine. However, if you do not want to go through all that trouble, Systrace can come to the rescue. For investigations, I run Firefox under Systrace with a systrace policy that allows connections only to Privoxy. All other connections attempts are denied and logged. It is interesting to see how many connections Firefox tries to do all by itself that do not go via the proxy. There are update pings, and all kinds of other connections.

In this case, Systrace is not being used against an adversary but rather against an untrusted application. It works quite nicely at that, too.
Categories: Systrace
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The Name of the Wind

The Name of the Wind by Patrick Rothfuss is one of the best fantasy books that I have read lately. I literally spent a whole weekend reading the book from start to finish. The book tells the story of Kvothe, a musician and arcanist, who has achieved almost legendary status and mysteriously vanished. Kvothe is now a bar keeper in a little town of no particular importance. His story is being told as a biography. It is superbly written and I am really looking forward to the next two books!
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Libevent 1.4.5-stable released

I am happy to announce the release of libevent 1.4.5-stable. You can download the source here:
There have been a few bug fixes since 1.4.4-stable. Here's a brief summary:

  • Several HTTP fixes
  • Fixed the Windows port
  • correctly generates fixed length entries now

See the changelog for full details.

We would like to thank the people who have reported bugs including Forest Wilkinson, liusifan and others. To report a bug, make a feature request, or submit code, you can use our sourceforge interface here.
Categories: Libevent
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