OSEC

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Re: Trojan modifying ntdll.dll and cmd.exe

From: Harlan Carvey (keydet89yahoo.com)
Date: Fri May 16 2003 - 05:57:21 CDT


Eric,

I'd like to ask a couple of questions, to get some
clarification.

> We have encountered a trojan that has modified both
> cmd.exe and
> ntdll.dll on a Windows 2000 machine. The files
> failed our CRC check
> (TDS was used for this, these out of 29 CRC-checked
> files were flagged
> as modified and Windows also flagged it).

What is "TDS"? It sounds as if it might be Tripwire,
but I'm not familiar w/ the acronym.

What were the other 27 files that were "modified"?

How did Windows flag this?

> It was installed on a well
> protected machine (behind a firewall, zone alarm,
> Norton anti-virus,
> locked-down) and believe the application installing
> it was either a
> vendor-installed patch this morning (we have
> notified the vendor and
> are getting their feedback and verifying) or through
> a web-based IE
> exploit on a fully patched IE installation.

Interesting. Were there any other installations,
perhaps a patch?

Also, what leads you to think that an IE-based exploit
is involved? Is this speculation, or do you have hard
evidence that points to this? If you have evidence,
can you share it? It might point out the signature
you're looking for.

> Has anyone on this list encountered a trojan
> specifically targetting BOTH of
> these files? Clearly many target cmd.exe and both
> (cmd.exe and
> ntdll.dll) are great candidates for modification by
> a hacker. Cmd.exe
> has of course been swapped-out since the beginning
> of time. We'd like to
> learn more about the signature of this particular
> one.

I'm not entirely clear on a couple of things. First,
you're right that a recent exploit does target
ntdll.dll, but not for modification...the exploit is a
buffer overflow. Second, I'm not clear on what you
mean by cmd.exe being a "great candidate for
modification" or having been "swapped-out since the
beginning of time".

To be quite honest, there isn't anything in the post,
other than the subject line, to suggest that a Trojan
was involved.

I think that there's a much simpler explanation to
this, one that can be found through the collection and
analysis of hard data...process list, installed
services and drivers, port-to-process mapping, etc.

Hope that helps...I'd really appreciate any
information you can provide to clear this up a bit.

Thanks,

Harlan

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