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Re: Announcement: Solaris loadable kernel module backdoor
From: pedward () WEBCOM COM (pedward () WEBCOM COM)
Date: Tue, 21 Dec 1999 14:33:50 -0800


With the proliferation of these types of backdoors, is there any way to
prevent your 'r00t3d' box from being backdoored?

A simple approach for Linux would be something like this:

At boot, compile the list of modules that are 'known good' (for the sake
of argument, it's the /lib/modules/x.y.z), then write the list, with
MD5 checksums, to a write once /proc interface to kmod.

kmod would check the MD5 sum before loading the requested module, if it didn't
match the in-kernel list, don't allow it.

For the write once, you'd have a 0600 /proc entry, that upon writing a
^D, it would change it to 0000.

For the really paranoid, at compile time you could tar up all the modules and
create the MD5 sum of that, store it in the kernel at some spot, and modify
the module utils to read tarfiles.  If the MD5 sum of the tarfile doesn't
match the compiled in list, you can't load the module.

Any other ideas on preventing untrusted modules from being loaded or replaced
and loaded as an existing 'trusted' module?

--Perry


I'd like to announce in addition to the two THC articles covering Linux
and FreeBSD loadable kernel module backdoors the first public loadable
kernel module backdoor for Solaris.

Regards,
Plasmoid / THC
http://www.infowar.co.uk/thc
http://www.pimmel.com



--
Perry Harrington                 Director of                   zelur xuniL  ()
perry () webcom com             System Architecture               Think Blue.  /\



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