It seems finally someone has found a flaw in the way Tor works, a way to beat it and find out who is using the system.

Perhaps an end to the most anonymous system on the Internet?

I got this info fresh from SANS.

One of our readers sent in a very worrying analysis of what appeared to be “traffic modification” (in his words) on the part of the Tor network.

The Tor (“The Onion Router”) network is an anonymizing peer-to-peer network of routers on the Internet which uses various techniques to bounce traffic around the Internet in such a way that traffic analysis becomes difficult if not impossible to perform. Tor is a perfect example of a dual-use technology: it can be used to avoid government-imposed Internet censorship or to protect the identity of a corporate whistleblower but at the same time it is sadly ideal for various nefarious uses.

It seems to point to traffic modification on an exit node, packetstorm in particular.

The key tenet of Tor is that it should protect anonymity and the reader’s analysis pointed not only to traffic modification on the part of a so-called “exit router” (the last hop in a Tor circuit before your packets reach the real destination) but also an attempt at tracking the true origin of the traffic (in a Tor network a hop only knows that the traffic comes from a previous hop but no futher back).

Both William Salusky and myself looked into the data and it seemed to implicate packetstormsecurity.org, an exit router in Denmark and, more curiously, a DNS tunnel to transmit data out (via obviously fake hosts under the t.packetstormsecurity.org domain). This last item was interesting because it replicated data which was apparently being submitted to the host via an HTTP cookie so it seemed that the idea was to have the cookie travel to the unwitting Tor user and be sent back via DNS tunnel to an external host to confirm the real identity of the host. As both of us were busy we looked a little deeper but ultimately we recommended that the reader report this to the Tor authors.

A quote from the actual paper.

Clearly Tor’s designers have done a pretty good job: I couldn’t find any weakness in Tor itself that violate the tenets set out at http://tor.eff.org/ (basically that end-to-end traffic analysis is always possible, but the traffic analysis should [be] difficult to everything but a global Echelon). So instead, I attacked the data which Tor carries the most of: web traffic.

Worrying indeed, you can download the paper here:

“Practical Onion Hacking” by Andrew Christensen

Source: SANS