Re: one of my servers has been compromized

[John Jacobs <flamdugen () hotmail com>]

> Sounds pretty neat to be honest. But one thing I'm wondering is that if  
> they have root, what's stopping them from turning that off? After all  
> they need root to load the modules in the first place, so if they are  
> in a position to want to do that, then they are in a position to turn  
> that off. Granted they probably wouldn't be able to load modules till  
> next boot(at least Id probably cry if that wasn't the case) but even  
> that can be a win scenario depending on how they want to execute the  

Hi Gage, thank you for your reply.  What you are missing is that by disabling kernel module loading you are applying a 
defense-in-depth strategy to prevent a *vulnerable* module from automatically loading in the first place resulting in 
root compromise.  I believe you may not be aware that some modules are loaded automatically if a corresponding special 
device is accessed.  Usually the userspace modprobe utility is executed though this can be controlled by the value of 
/proc/sys/kernel/modprobe

Preventing module loading has historically be a valuable way to prevent privilege escalation or further root 
compromise.  Such an example would be the 'ptrace' exploit, see 
http://www.sans.org/security-resources/malwarefaq/Ptrace.php

Historically there have been various kernel modules that are vulnerable that could be loaded by userland non-root 
programs or access.  Ubuntu likes to automatically load modules.

Removing CAP_SYS_MODULE or kernel.modules_disabled=1 make good security sense.  See 
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=3d43321b7015387cfebbe26436d0e9d299162ea1
 and 
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=25354c4fee169710fd9da15f3bb2abaa24dcf933
 and https://wiki.ubuntu.com/Security/Features#block-modules

The goal here is defense in depth.  Revocation of loading the kernel modules cannot be undone unless a system reboot is 
effected which should be highly suspicious.

The goal isn't about protecting ones boxens from a theoretical boogie-man it is to leverage all available and sane 
methods for properly securing ones box.  I see no point to to use these options.

Thanks,
John


                                          
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