Full Disclosure mailing list archives
Re: Bypassing "smart" IDSes with misdirected frames?
From: Michal Zalewski <lcamtuf () coredump cx>
Date: Fri, 28 May 2004 01:48:21 +0200 (CEST)
On Thu, 27 May 2004, Alexander E. Cuttergo wrote:
If the attacker is on the same LAN as your IDS, you have many problems more severe than the attack you have described.
In a sufficiently complex network, you are going to face internal threats. Simply, if you have 1000 or 10000 employees, it is foolish to assume they are all going to play nice. Installing internal IDSes, firewalls and whatnots is a way of mitigating and managing the risk. Most of IDS vendors have solutions that can be plugged internally. I would not even bother to post if IDSes were not commonly used in such a setup.
More generally, if you can send a packet which is accepted by the IDS and not by the target host, you can bypass IDS. Another example is sending packets with low ttl; this even does not require access to the same LAN.
You won't be able to do this in a reasonable IDS setup (span port or bridge mode).
A packet which is not accepted by the recipient will not elicit an ACK frame.
One that is does not have to do this, either. Window size, etc. -- ------------------------- bash$ :(){ :|:&};: -- Michal Zalewski * [http://lcamtuf.coredump.cx] Did you know that clones never use mirrors? --------------------------- 2004-05-28 00:04 -- http://lcamtuf.coredump.cx/photo/current/ _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html
Current thread:
- Bypassing "smart" IDSes with misdirected frames? Alexander E. Cuttergo (May 27)
- Re: Bypassing "smart" IDSes with misdirected frames? Jason (May 27)
- <Possible follow-ups>
- Re: Bypassing "smart" IDSes with misdirected frames? Michal Zalewski (May 27)