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Advanced Intrusion Defense
Joel SnyderOpus One
Acknowledgements
http://infosecuritymag.techtarget.com/
Massive Support from Marty Roesch, Ron Gula, Robert Graham
Products from ISS, Cisco, and Tenable
Cash and Prizes from Andy Briney and Neil Roiter
This is an IDS alert…
• IDS saw a packet aimed at a protected system
• IDS magic decoder technology correctly identifies this as “Back Orifice!”
This IDS alert ain’t no good
• Last time I checked, FreeBSD 4.9 was not one of the supported platforms for BackOrifice…
Please don’t call that a False Positive
• IDS developers will jump down your throat
• “False Positive” means the IDS cried wolf when there was no such attack Usually the result of
poorly written signatures
• Instead, let’s invent a complex multisyllable term:“non-contextual alert”
The IDS lacks “context”
• IF the IDS knew that the destination system was not running Windows…
• IF the IDS knew that the destination system was not running Back Orifice…
• IF the IDS knew that there was no such destination system…
• IF the IDS knew that the destination system was more hops away then TTL allowed…
IF IF IF the IDS knew more…
• THEN the IDS could tell the IDS operator more about this attack
• Ron Gula (Tenable) says that alerts are “raw intelligence.” They are data, but are not information yet. We need to turn them into “well-qualified intelligence” to start a war.
Roesch: “Target-Based IDS”
• Target-based IDS Sensor The sensor has
knowledge about the network
The sensor has knowledge about the hosts
• Target-based Event Correlation The output of the
sensor is compared to knowledge of vulnerabilities
Target-based IDS has two components
Target-based IDS sensor
• Network Flight Recorder (NFR) and Internet Security Systems (ISS) claim to be shipping IDS sensors that have target-based IDS technology in them
• Sourcefire is working on putting this into its sensor
• Other vendors may be including this technology (but I don’t know about them)
Target-based IDS Consoles
• Information Security asked me to look at three “Target-based IDS” consoles
Internet Security Systems “Fusion” Cisco “Cisco Threat Response” Tenable Security “Lightning Console”
Start with a normal IDS…
1. IDS sensors generate enormous dinosaur-sized piles of alerts;alerts are sent to the IDS console
2. Operator gets enormous dinosaur-sized headache looking at hundreds of thousands of alerts … and add
brains!
Brains=knowledge + process
Knowledge
• Somehow figure out lots of information about What systems are
out there What software they
are running What attacks they
are vulnerable to
Process
• Evaluate each alert with the additional contextual knowledge and decide To promote the
alert To demote the alert That we don’t know
Approach 1: ISS Fusion
1. NetMgr schedules scanning using ISS Scanner
2. Scan info, including ports & vulnerabilities, flow into SiteProtector
3. Sensor alerts also flow into SiteProtector
4. Fusion reads alerts and assigns priorities for the operator
Variation 2: Tenable Lightning
1. NetMgr schedules “active scans” using Nessus or NeWT
2. Results are sent to Lightning Console
3. Passive scan results are collected by NeVO
4. Passive results are sent to Lightning
What is “Passive Scanning?”
By simply watching the traffic fly by, you can learn a great deal
• TCP connections have “fingerprints” Fingerprints are useful for identifying the TCP
stack (hence: the O/S) involved Existence proof
• Applications (client & server) have “banners” Banners can reveal application names, version
numbers, and patch levels
Tenable (continued)
5. IDS sensors send alerts to console (Bro, Snort, ISS, Enterasys, NAI)
6. Lightning compares every alert to the known vulnerability database, rejecting all that don’t match an identified vulnerability
Approach 3: Cisco CTR
1. IDS sensors send alerts to their native console
2. Copies of alerts also go to CTR
3. CTR investigates alerts4. Alerts plus
investigation are available to operator
Scan before vs after
• If you scan before… You can’t verify that
an attack actually succeeded
Your scan will always be out of date
• If you scan/verify after… You can verify that
an attack did something
You might be a day late (and a dollar short) to catch things
You potentially can create a DoS condition
Do they work?
• Yes, but… Be careful what you
wish for
• All products had a significant reduction in IDS alerts
• Caveats CTR - rolling
window of only 1000 events!
Lightning - only shows events with matched vulnerabilities!
What about scanning?
• When you scan is important
• How you scan is important
• Where you scan is important
• Caveats Scanning after the
fact can be a problem
Scanning before the fact can be a problem
Passive scanning can miss things
Active scanning can miss things
Can this quiet my IDS down?
• It could…
• But none of the products I looked at have a feedback loop to the IDS!
• Why don’t the scanners tell the IDS what ports to look on?
• Why don’t the scanners tell the IDS what signatures to ignore?
Is this right for you?
YES!• “I already have an IDS
and I care about the alerts and I need some way to help prioritize them because I am drowning in alerts!”
• “I need to get an IDS for alerts but don’t have the manpower to analyze the alerts.”
NO!• “If I get this, my IDS
will be a self-tuning smooth-running no-maintenance machine.”
• “I have no network security policy that says what to do when an alert occurs.”
Questions?
Submit your questions to Joel by clicking on the Ask A
Question link on the lower left corner of your screen.
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