Re: Signature for CVE ID: CVE-2008-1151 (CISCO PPTP memory leak - DoS)

["Secure Scorp" <securescorp () gmail com>]

This vulnerablity as described by Cisco occurs when the PPTP session
is terminated. Please note it states 'terminated'. If terminates means
log off then it means that a legitimate active connective has logged
off etc. For this vulnerablity to be exploited the user should be a
legitimate user.I think it is difficult to write a signature for such
legitimate users.Even if we write any signatures, we are bound to get
false positives as you correctly mentioned. There is no possible work
around in the Cisco configuration as well.

 I don't think so that anyone can carry out DoS to exploit this
vulnerablity.If we still want to write some signatures then we should
write it for TCP 1723 and GRE (protocol 47) with higher rate OR only
on TCP 1723 as it is the connection channel.

 Cisco has released a software to address this issue. The best and
fastest way to go about this vulnerablity is to patch the router than
spending resources on writing signatures which are bound to give false
positives.

Note: PPTP initiates/terminates the connections on TCP 1723 and the
data is sent using/encapsulating GRE (protocol 47).

Thanks,
Aditya Govind Mukadam

On Fri, Jul 4, 2008 at 9:33 PM, Ravi Chunduru
<ravi.is.chunduru () gmail com> wrote:
> Please see these links for more information on vulnerability:
>
> http://nvd.nist.gov/nvd.cfm?cvename=CVE-2008-1151
> http://www.cisco.com/en/US/products/products_security_advisory09186a0080969862.shtml
>
> According to this vulnerability report,  PPTP process in CISCO routers
> leak memory upon every PPTP termination. Eventually memory is used up
> and no other PPTP connections are entertained.
>
> How does one go about writing signatures for detecting exploits
> targeting this vulnerability?
> Only possibility I can think of, based on capabilities of signature
> language, is to check for the rate at which these PPTP connections are
> made. If it checks for higher rate, there could be false negatives
> where attacker makes the connections at very slow rate.  If it checks
> for lower rate,  then there is possibility of false positives. What is
> the right way of writing signatures?
>
>
> thanks
> Ravi
>
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