Re: [gentoo-user] Re: chkrootkit LKM trojan ?

[Dave S]

On Sunday 16 July 2006 21:52, dnlt0hn5ntzhbqkv51 wrote:
> On Sun, 16 Jul 2006 15:54:18 -0400, Dave S <gentoo@××××××××.net> wrote:
> > On Sunday 16 July 2006 19:54, Hemmann, Volker Armin wrote:
> >> On Sunday 16 July 2006 20:25, Dave S wrote:
> >> > HI, I have a potential security problem ...
> >> >
> >> > and err its not on gentoo, its on ubuntu but I am not getting any
> >> > response there & you guys are the most tech bunch I know  - Thought I
> >> > would lay it on the table :)
> >> >
> >> > I just had an email from chkrootkit last night -
> >> >
> >> > ---
> >> >
> >> > The following suspicious files and directories were found:
> >> >
> >> > You have     3 process hidden for readdir command
> >> > You have     3 process hidden for ps command
> >> > chkproc: Warning: Possible LKM Trojan installed
> >> >
> >> > ---
> >> >
> >> > Running chkrootkit now and all is OK
> >> >
> >> > root@dave-comp:~#
> >> > root@dave-comp:~# chkrootkit | grep chkproc
> >> > Checking `lkm'... chkproc: nothing detected
> >> > root@dave-comp:~#
> >> >
> >> > I have even 'sudo install --reinstall chkrootkit' in case its binarys
> >> > have been modified (paranoid)
> >>
> >> if you installed using the tools of the system, it could be worthless,
> >> because compromised. Boot from a cd and check from the cd.
> >
> > I understand. Booted from knoppix 5.0.1, executed a
> >
> > 'chroot /mnt/hda1 chkrootkit' and a
> > 'chroot /mnt/hda1 rkhunter -c'
> >
> > - both scans brought back nothing. From what I have read the chkrootkit &
> > rkhunter binarys would have been from the CD and therefore untainted ?
> > Am I
> > correct ?
> >
> > Are there any other checks I can do - re-installing the system is not my
> > preferred option :)
> >
> > Dave
>
> I'm a newbie, so discount this appropriately.
>
> 1. IIUC, running rkhunter/chkrootkit from knoppix simply checks the
> knoppix cd.
> 2. You want second/third opinions. IIWU,
>        i. I'd scan the box with a Trojan signature scanner - e.g. fprotect,
> AntiVir, etc.
>        from Knoppix - first assuring that you have current signatures.
>        ii. I'd reemerge/recompile the kernel WITHOUT modules or module
> support, and clear out your usr/lib/modules         (though IIUC, this
>         can be foiled).
>        iii. I'd try zeppoo.
> 3. Try to figure out how you got it. e.g. you installed software from an
> unreliable source; your privileges are screwed up; you have an unpatched
> server(s) running; etc.

I am pretty picky about my software - have not messed with permissions & its a 
desktop machine not running any external services.

>
> Maybe.... you could find the both the vector and the lkm  -  but
> understanding that the only real solution to a
> rootkit is restoring from a clean backup, or rebuilding :-(

... gulp ... On digging around and listening to you guys I am going to go with 
a false +ve. My clue came when I discovered how chkrootkit detected the 
problem ...

How accurate is chkproc? 
 If you run chkproc on a server that runs lots of short time processes it 
could report some false positives. chkproc compares the ps output with 
the /proc contents. If processes are created/killed during this operation 
chkproc could point out these PIDs as suspicious.

That fits in with the fact that chkrootkit & rkhunter now report clean (& also 
fits in with someone tinkering from the inside !)

I will keep a slightly suspicious eye on the box from now on :)

Cheers

Dave 




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