It is interesting to observe, that Tor exit nodes with out-of-date OpenSSL implementations can themselves be affected by the Heartbleed bug.

Can Heartbleed expose a Tor user's IP address merely by exploiting the vulnerable Tor exit node, or would all relay servers in the chain have to be vulnerable as well (and simultaneously exploited), and the entire chain of requests 'decoded' piece by piece to unmask the original user's IP address?

In other words, how robust is Tor anonymity from the Heartbleed bug? (In terms of IP address)

2 Answers 2


The exit node does not know your IP address -- that's the whole point of onion routing. Rather, it knows which relay node to contact in order for the data to eventually get back to you. In order for your IP address to be revealed with certainty, the entire chain needs to be vulnerable; if the entry and exit nodes are both vulnerable, an attacker can make a reasonable guess as to your IP by correlating the use of relay nodes.


Tor recently started to reject all the servers which have not updated their SSL. There is also initiative to block any servers that come online with unpatched SSL in the future. These cuts result in ~12% network capacity drop for Tor. That resulted from blocking ~380 servers.

Below is an excerpt from the message on Tor's mailing list:

I thought for a while about taking away their Valid flag rather
than rejecting them outright, but this way they'll get notices
in their logs.

I also 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.

If the other directory authority operators follow suit, we'll lose about
12% of the exit capacity and 12% of the guard capacity.

I/we should add to this list as we discover other relays that come
online with vulnerable openssl versions.

Also these are just the relays with Guard and/or Exit flags, so we should
add the other 1000+ at some point soon.

More info on mailing list: https://lists.torproject.org/pipermail/tor-relays/2014-April/004336.html

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