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Re: security idea - bootable CD to check your system



Thanks for the encouragement. I've been looking into it a bit more, and I'm not sure that it would be possible for me to build this by myself, as it would need changes to the debian ftp archive to work. I.e. you would need there to be a retrievable list of filenames and checksums for every package in the debian 'pool' archive, which doesn't exist at present. E.g. for every '.deb' file, there would be a '.deb.sums' file in the same directory. So unless someone at debian thinks it's a good enough idea to justify adding this information to the archive, I don't think it's going to happen as I originally thought. Another way to do it is to keep all of the package files that have been used to build the system on the machine's hard disk, check them first using the checksums in 'Packages.gz', and then retrieve the md5sums for the individual files from the locally archived packages.

You could avoid the problem of people adding files by also generating a list of all the files in certain directories (/bin, /lib, /usr) which don't match an installed package. This list should hopefully be small and manageable enough that someone could scan through it quickly to see if anything odd has changed.

As I said in my first email, I'm not sure if I'm up for trying to do this all by myself, but I'll let you know if I do make a start on it.

cheers,

andy

Bernhard R. Link wrote:
* andy baxter <andy@earthsong.free-online.co.uk> [070624 18:19]:
I've tried using debsums - however it's not really a good check on your system because the program and the data it's using both come from the system you are trying to check, so could be compromised. Also, it seems to miss out many important packages - e.g. here's the standard error output from a recent run of debsums on my server:

I had someone in the past considered this, too. First of all debsums's
main advantage is looking for unintended changes (and its indeed a shame
so many of the important packages come without, that makes bad RAM or
unreliable controlers a much larger hassle than they needed to be).

To make anything security relevant out of them, the CD would need to
have checksums of the contents of those files (for the different
versions of the packages) and the missing md5sum files on it.

But even that would only make sure none of the official files are
changed, while it is more easy to cause harm by simply adding stuff.
(Even changing can happen by just uninstalling and puting the stuff
manually in there).

So the whole thing would have to be combined with something like a
security focused checker (perhaps similar to cruft).

That together with some code to automatically detect the system and
use the right partitions at the right place would surely be a nice tool,
but if would for sure be an enourmous amount of work before anything
halfly usefull comes out of it.

So good luck and let me know when it is finished. (Because I doubt
anyone else will find the time to do it).

Hochachtungsvoll,
	Bernhard R. Link





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