IDS mailing list archives
Re: Announcement: Alert Verification for Snort
From: Martin Roesch <roesch () sourcefire com>
Date: Wed, 22 Oct 2003 23:22:05 -0400
Hi Chris,Just to make a point of semantics, I'd like to comment on the "reduce the large number of false positives produced by intrusion detection systems such as Snort" quote from your post.
I spent some time a couple months ago talking about the misconceptions of "false positives" in Snort on this very list and I think there's a valid point to be made here. Let me enumerate the cases you can have as I see it:
1) Detect, Attack Present, Vulnerable: True Positive2) Detect, Attack Present, Not Vulnerable: Nontextual (i.e. detect requiring contextual data to resolve)
3) Detect, No Attack, [vuln|not vuln]: false positive 4) No Detect, Attack Present, Vulnerable: False Negative 5) No Detect, Attack Present, Not Vulnerable: ? 6) No Detect, No Attack, [vuln|not vuln]: Don't care (true negative?)In case 2 the "nontextual" isn't a false positive but I think that most people are calling it an FP these days. I *personally* think that's a misconception. What we have in that case is a *real attack* that your IDS is detecting exactly as it was asked to. Just because it doesn't have the additional information about the context or relevance of the event isn't a problem with the IDS, it's a side effect of the way that NIDS have been built for the past 10 years.
Case 3 is where we have the true false positives, the NIDS is detecting attacks that aren't occuring on the network. I think that case 2 happens far more than case 3 with systems like Snort, which is why I think it's important to make the distinction between "real" false positives (i.e. the IDS screwed up) and nontextuals where the IDS has done its job, it just needs more information to properly evaluate the reality and priority of the event.
I hope this is making sense to everyone here, please let me know if you have any questions. Looks like a neat tool Chris!
-Marty On Oct 21, 2003, at 9:16 PM, Christopher Kruegel wrote:
[Please excuse multiple copies of this message]Alert Verification is a technique to reduce the large number of false positives produced by intrusion detection systems such as Snort. The idea is to actively probe for the vulnerability that is exploited by a certain detected attack. When the victim is not vulnerable, the alert can be simply discarded or tagged with a low priority.William Robertson has implemented an extension for Snort that implements Alert Verification. Patches for the current version of Snort (2.0.2) and additional information are available underhttp://www.cs.ucsb.edu/~wkr/projects/ids_alert_verification/ Please send any comments or bug reports to snort-av () cs ucsb edu----------------------------------------------------------------------- ----FREE Whitepaper: Better Management for Network Security Looking for a better way to manage your IP security? Learn how Solsoft can help you: - Ensure robust IP security through policy-based management - Make firewall, VPN, and NAT rules interoperable across heterogeneous networks - Quickly respond to network events from a central console Download our FREE whitepaper at:http://www.securityfocus.com/sponsor/Solsoft_focus-ids_031015 ----------------------------------------------------------------------- ----
-- Martin Roesch - Founder/CTO, Sourcefire Inc. - (410)290-1616 Sourcefire: Snort-based Enterprise Intrusion Detection Infrastructure roesch () sourcefire com - http://www.sourcefire.com Snort: Open Source Network IDS - http://www.snort.org --------------------------------------------------------------------------- FREE Whitepaper: Better Management for Network Security Looking for a better way to manage your IP security? Learn how Solsoft can help you: - Ensure robust IP security through policy-based management - Make firewall, VPN, and NAT rules interoperable across heterogeneous networks - Quickly respond to network events from a central console Download our FREE whitepaper at:http://www.securityfocus.com/sponsor/Solsoft_focus-ids_031015 ---------------------------------------------------------------------------
Current thread:
- Announcement: Alert Verification for Snort Christopher Kruegel (Oct 21)
- Re: Announcement: Alert Verification for Snort Martin Roesch (Oct 22)
- Re: Announcement: Alert Verification for Snort Aaron Temin (Oct 23)
- Re: Announcement: Alert Verification for Snort Michael Stone (Oct 23)
- Re: Announcement: Alert Verification for Snort Martin Roesch (Oct 23)
- Re: Announcement: Alert Verification for Snort Sam f. Stover (Oct 23)
- Re: Announcement: Alert Verification for Snort Christopher Kruegel (Oct 23)
- Re: Announcement: Alert Verification for Snort Sam f. Stover (Oct 23)
- Re: Announcement: Alert Verification for Snort Martin Roesch (Oct 24)
- Re: Announcement: Alert Verification for Snort Martin Roesch (Oct 23)
- Re: Announcement: Alert Verification for Snort Randy Taylor (Oct 23)
- Re: Announcement: Alert Verification for Snort Aaron Temin (Oct 23)
- Re: Announcement: Alert Verification for Snort Michael Stone (Oct 24)
- Re: Announcement: Alert Verification for Snort Martin Roesch (Oct 22)