Re: [cobalt-security] has my machine been hacked

[Michael Stauber <cobalt@xxxxxxxxxxxxxx>]

Hi Kelly,

> Checking `lkm'... You have     1 process hidden for readdir command
> You have     1 process hidden for ps command
> Warning: Possible LKM Trojan installed
>
> Can somebody tell me if i've been hacked and if so, what must i do.
> Thank you, all help is greatly appreciated.

The hidden process check in chkrootkit can and will sometimes report hidden 
processes when there are none. Please be aware of these *false* alarms which 
will happen mostly when you're running many dynamic processes. Like Apache, 
MySQL or ASP. 

Why does it happen? Chkrootkit compares the processes in the /proc/ directory 
with those shown by the command "ps". If both outputs don't match, then it'll 
give alert. However, the comparision takes a few moments and if a process 
ends (naturally or forced) during the comparision, then that will cause an 
false alarm.

You shouldn't trust the LKM test in chkrootkit fully and should run some 
manual checks to see what's up if you're warned about a possible LKM.

How to run the test manually for cross checking:

As root:

 cd /home/security/chkrootkit/ (or to wherever your chkrootkit is installed)
 ./chkrootkit -x lkm

That will show a detailed listing of the suspicious processes in question and 
can help you to look further into the issue. If the listing comes up empty 
(see example below), then there is nothing to worry about.

[root admin]# cd /home/security/chkrootkit/
[root chkrootkit]# ./chkrootkit -x lkm
ROOTDIR is `/'
###
### Output of: ./chkproc -v
###

However, if it returns a couple of numbers, then those are the process IDs of 
the hidden processes. If repeated runs of "chkrootkit -x lkm" report such 
process IDs, then you should indeed be worried.

-- 

With best regards,

Michael Stauber
mstauber@xxxxxxxxxxxxxx
Unix/Linux Support Engineer