(Other content servers did require you to know the password.) A number of the unprotected content servers had copies of copyrighted ebooks, making them de facto pirate servers (essentially mini Internet Archives). They didn’t require a password or any other type of authentication. One thing I did notice is that a number of the calibre content servers that I could access were completely open. Or so the results suggest most of the data is behind a paywall. For examples, the IP addresses for these content servers are concentrated in the biggest ebook markets (US, UK, Germany, France), and the most commonly used OSes were Windows 7, Windows 8, and a really old version of Windows 7. We can see all sorts of interesting details from the Shodan results. (I say 'around' because some results are false positives.)

They did indeed find calibre content servers running on the open web according to the results page on Shodan, there are around 1,863 instances running right now. Using Shodan.io, we can search for the keyword Calibre in the server HTTP header. In it’s default configuration, Calibre does not require any authentication to access the web interface.

Knowing this and being a pentester by trade, I became quite curious if there was any notable presence of Calibre on the internet. It’s capable of running a server to allow remote users to browse and download books. Calibre is an open source e-book management application, and probably one of the most popular. They allow you to carry and travel with hundreds of books. I love reading, and I especially like my e-readers. But according to one computer security expert, around 1,800 other people aren’t as cautious. I’ve tested using calibre as an online content server a few times, but I never left it running because I didn’t want to find out the hard way that a hacker could exploit calibre and gain access to the rest of my files on my system. One of its lesser known features is the ability to act as a content server either on a local network or on the web. Calibre is Being Used to Run 1,800 Online Content Servers – including De Facto Pirate ServersĬalibre is a widely used ebook library tool that can convert ebooks to and from just about any format and help you load said ebook on to just about any device.

Calibre server