Saturday, May 2, 2009

Filtering What Goes Into Your History

When I tell people about ShellSink, many of them say, "hey, that's a great idea!" Then the little sysadmin perched on their shoulder crosses her arms and shakes her head. "Tsk, tsk. Storing your shell history on a remote server is not secure!", she says. This is absolutely true. Not only is your bash history passed via an insecure Http connection, but then it is stored unencrypted on Google's servers where a rogue Google employee, someone who hacked Google, or a rogue ShellSink admin could access them. Don't use shellsink on a system that needs to be ultimately secure!

However, Shellsink is safe to use. If you use Google for email, calendar, documents, etc. then you already trust them with information that is probably more sensitive than your shell history. And if you don't trust me you can download the ShellSink source code and spin up your own server using Google's AppEngine. In any case you should still take some basic precautions. Most importantly, never use inline passwords!! ShellSink will send anything your bash history captures.

Here are several ways to safeguard yourself against sending sensitive information to ShellSink. One technique is to add the following to your .bashrc:
Now any command you precede with a space will NOT be captured by the history, and thus will not be sent to the ShellSink server. Another technique is to add the following to your .bashrc:
In this example any command that starts with netstat or sqlplus will automatically be ignored by the shell history and ShellSink. Both these techniques give you different granularity control over what gets sent to ShellSink. The first technique works on a per command basis and the second covers all commands.

Finally, there is the nuclear option:
shellsink-client -d
This completely disables ShellSink for all terminals. I don't really have much use for this one, but when you start to do something that you are ultra paranoid about, this is one way to be sure nothing is leaving your computer via ShellSink. To re-enable ShellSink simply do this:
shellsink-client -e

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