IDS mailing list archives
Re: Active response... some thoughts.
From: "mb_lima" <mb_lima () uol com br>
Date: Fri, 31 Jan 2003 14:34:34 -0200
Hi Paul, It is perfect your explanation, but an attacker can create ways to keep a sensor busy enough so that "if the sensor is fast enough" is not true. But I agree with you. TCP RST works fine for me. Best Regards, Marcelo
Actually, TCP RST is more than just a marketing solution. In practice, if the sensor is fast enough, a TCP RST can and often will prevent even single packet attacks. Here is why... A TCP RST does not cause orderly connection termination. It causes immediate connection termination. That is, the protocol stack is not required to deliver pending data and typically does not. If you also take into consideration that on most operating systems, applications are not dispatched immediately upon arrival of new data, there is a window of opportunity for the protocol stack to receive and process the RST even before the application can read the previously received data from the single packet attack! On most operating systems, when a process is moved from a wait queue to the run queue, it is not given immediate control of the CPU unless it has a "realtime" priority or the run queue is completely empty. Therefore, it will on average have to wait half a time slice before it can read its data. A typical time slice is 10ms. If the IDS can get the RST sent in under 5ms, it can often stop a single packet attack. The odds go up if the IDS is faster or the server is busy.On Tuesday, January 28, 2003, at 08:31 AM, Garbrecht,Frederick wrote:ummmm, just a technical quibble, but a TCP resetwouldn't work with theSapphire worm because it propagates using UDP astransport, notTCP.....It is just a minor quibble because the point is thatthe attack wascompletely contained in a single packet. The samewould have held trueif it was over a TCP/IP connection. Once the attackhas beencompleted, a TCP RST would provide no value. It isthe proverbialclosing the barn doors after the horse is alreadyout.RST is largely a marketing solution, not a technicalsolution.Todd__________________________________________________ Do you Yahoo!? Yahoo! Mail Plus - Powerful. Affordable. Sign up now. http://mailplus.yahoo.com
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Current thread:
- RE: Active response... some thoughts., (continued)
- RE: Active response... some thoughts. Ralph Los (Jan 26)
- RE: Active response... some thoughts. Christopher Lyon (Jan 26)
- RE: Active response... some thoughts. Alan Shimel (Jan 26)
- RE: Active response... some thoughts. Kohlenberg, Toby (Jan 28)
- RE: Active response... some thoughts. Garbrecht, Frederick (Jan 28)
- Message not available
- Re: Active response... some thoughts. Stone Cold (Jan 31)
- Message not available
- RE: Active response... some thoughts. Kohlenberg, Toby (Jan 28)
- RE: Active response... some thoughts. mb_lima (Jan 28)
- Re: Active response... some thoughts. Paul Palmer (Jan 31)
- RE: Active response... some thoughts. Rob Shein (Jan 31)
- Re: Active response... some thoughts. mb_lima (Jan 31)