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Heartbleed: (Almost) three years later


Shodan recently published a report on the state of Heartbleed which was picked up by lots of media outlets.

I took this as an opportunity to have a look at our statistics. Shodan performs its scan based on IP-addresses and makes the results searchable. also runs daily scans, but these are based on the list of domains under the Austrian ccTLD .at. We published a first report on these results in the summer of 2014. We're close to the three year mark now, which is a very long time the Internet. So how do our numbers look like in January 2017?

We start by a list of domains under .at and look for web and mail servers as found by MX and A records. For web servers, we use either the domain itself, or www.$domain. This gives the following frame for the rest of the graphs: the roughly 1.5 million domains under .at are served by 200 thousand web servers and 100 thousand mail servers.


Looking a the best TLS support these servers offer, we see that both for HTTPS (web) and SMTP (mail) about half of the servers support encrypted connections.


As the larger mail-servers are much more likely to support TLS than smaller ones, the percentage of domains who can receive emails over TLS is actually about 90%.

Testing all those servers for the Heartbleed vulnerability gives the following result:


The vulnerable server barely show on the graph, for both protocols they are about 0.12% of all servers and about 0.22% of all servers offering TLS.

Over time, the numbers have fallen in the usual long-tail drop-off curve. As the domain-list and domain to IP-address mappings are not refreshed daily, these refreshes show up as upward spikes in the graph. This implies that a part of the decline in vulnerable servers was caused by IP and domain churn.


What does this mean for Domains?

It's pointless to graph vulnerable vs. not-vulnerable domains, the bar for vulnerable servers is not visible. In numbers: 1557 domains (0.29% of all TLS-enabled ones) are still vulnerable on HTTPS, and 320 on SMTP (0.05%). Graphing the development yields:


This graph is a rough approximation as the historical domain to IP mappings are not kept in the system. Anyway, something weird is going on. Lets have a closer look with regards to how important single servers are for the overall domain score. For that we'll use a combined graph showing the contributions of each server to the total number as well as the cumulative distribution function showing how many servers you need to fix to achieve x% of the vulnerable domains (Excel calls it the "Pareto Line").

Let's start with the domains:


The largest mailserver contributes about a third of the vulnerable domains, take the first three and they cover half of the heartbleed-affected Domains. Those are run by a small ISP, a PR/web agency and a private person, respectively.

The same graph for HTTPS looks like this:


This is far more concentrated: The first server hosts 809 domains (about half of the total), the second one 480 and third one 11. About 100 server comprise the long tail of vulnerable servers hosting just one .at domain. Checking some of the domains on these servers shows that the first one is run by a local ISP/registrar and is used for domains that are not in use. The second one only serves "this domain is for sale".

Summary: While Shodan still found a good number of vulnerable servers on the Austrian Internet, these are mostly not the servers that host relevant content.

Author: Otmar Lendl

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