The impact of the HeartBleed Bug on Tor Anonymity

Pierluigi Paganini April 18, 2014

The presence of nearly 380 servers in the Tor Network, 12 percent of the exit capacity, running the vulnerable version of OpenSSL could have compromised user’s anonymity.

The Heartbleed bug is the flaw in the popular OpenSSL library that is scaring the security communities, many security experts hiphotesized that Intelligence agencies, including NSA, have exploited the bug to spy on protected communications and to steal sensitive information from affected systems. No doubts, the Heartbleed bug has a significant impact on server infrastructure and also on mobile industry, but what it its impact on Tor network?
The Heartbleed bug has a serious impact also on the online anonymity of Tor users, to better understand how it is possible, we must take in mind that in order to preserve the user’s experience online is made untraceable distributing the connections on unpredictable channels through a network of nodes.
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When a user accesses any resource on the visible web through Tor network, his IP address is masqueraded, the connection appears as originating from a Tor exit relay.
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A Tor Relay receives traffic on the Tor network and pass it along, particular Tor Relay are the Exit nodes, an exit relay in fact is the final relay that Tor traffic passes through before it reaches its destination.
The Tor anonymity could be compromised if an attacker is able to grab encrypted information from the nodes and it it possible is they run a version of OpenSSL library affected by Heartbleed bug.
To avoid the exploitation of the Heartbleed bug on the affected nodes, and consequent disclosure of sensitive information, Tor Project leader Roger Dingledine, has identified and rejected 380 vulnerable exit nodes suggesting that the exit nodes running the vulnerable versions of OpenSSL should be blacklisted from the network. Roger invited to include again the node in the network only after that they will be upgraded.
If the other directory authority operators follow suit, we’ll lose about 12% of the exit capacity and 12% of the guard capacity,” he writes on the software’s mailing list.
The impact is critical, 380 nodes represent nearly 12 percent of the exit capacity, the Heartbleed bug could be exploited to compromise a vulnerable exit node and capture traffic data related to users anonymous connections.
I thought for a while about trying to keep my list of fingerprints up-to-date (i.e. removing the !reject line once they’ve upgraded their openssl), but on the other hand, if they were still vulnerable as of yesterday, I really don’t want this identity key on the Tor network even after they’ve upgraded their OpenSSL,” Dingledine wrote.
Anyone who had abilities to exploit the HeartBleed bug in the past months, has probably broken the cloak of anonymity which lie Tor users.

Pierluigi Paganini

(Security Affairs –  Tor, HeartBleed Bug)

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