- •Network Intrusion Detection, Third Edition
- •Table of Contents
- •Copyright
- •About the Authors
- •About the Technical Reviewers
- •Acknowledgments
- •Tell Us What You Think
- •Introduction
- •Chapter 1. IP Concepts
- •Layers
- •Data Flow
- •Packaging (Beyond Paper or Plastic)
- •Bits, Bytes, and Packets
- •Encapsulation Revisited
- •Interpretation of the Layers
- •Addresses
- •Physical Addresses, Media Access Controller Addresses
- •Logical Addresses, IP Addresses
- •Subnet Masks
- •Service Ports
- •IP Protocols
- •Domain Name System
- •Routing: How You Get There from Here
- •Summary
- •Chapter 2. Introduction to TCPdump and TCP
- •TCPdump
- •TCPdump Behavior
- •Filters
- •Binary Collection
- •TCPdump Output
- •Absolute and Relative Sequence Numbers
- •Dumping in Hexadecimal
- •Introduction to TCP
- •Establishing a TCP Connection
- •Server and Client Ports
- •Connection Termination
- •The Graceful Method
- •The Abrupt Method
- •Data Transfer
- •What's the Bottom Line?
- •TCP Gone Awry
- •An ACK Scan
- •A Telnet Scan?
- •TCP Session Hijacking
- •Summary
- •Chapter 3. Fragmentation
- •Theory of Fragmentation
- •All Aboard the Fragment Train
- •The Fragment Dining Car
- •The Fragment Caboose
- •Viewing Fragmentation Using TCPdump
- •Fragmentation and Packet-Filtering Devices
- •The Don't Fragment Flag
- •Malicious Fragmentation
- •TCP Header Fragments
- •Teardrop
- •Summary
- •Chapter 4. ICMP
- •ICMP Theory
- •Why Do You Need ICMP?
- •Where Does ICMP Fit In?
- •Understanding ICMP
- •Summary of ICMP Theory
- •Mapping Techniques
- •Tireless Mapper
- •Efficient Mapper
- •Clever Mapper
- •Cerebral Mapper
- •Summary of Mapping
- •Normal ICMP Activity
- •Host Unreachable
- •Port Unreachable
- •Admin Prohibited
- •Need to Frag
- •Time Exceeded In-Transit
- •Embedded Information in ICMP Error Messages
- •Summary of Normal ICMP
- •Malicious ICMP Activity
- •Smurf Attack
- •Tribe Flood Network
- •WinFreeze
- •Loki
- •Unsolicited ICMP Echo Replies
- •Theory 1: Spoofing
- •Theory 2: TFN
- •Theory 3: Loki
- •Summary of Malicious ICMP Traffic
- •To Block or Not to Block
- •Unrequited ICMP Echo Requests
- •Kiss traceroute Goodbye
- •Silence of the LANs
- •Broken Path MTU Discovery
- •Summary
- •Chapter 5. Stimulus and Response
- •The Expected
- •Request for Comments
- •TCP Stimulus-Response
- •Destination Host Listens on Requested Port
- •Destination Host Not Listening on Requested Port
- •Destination Host Doesn't Exist
- •Destination Port Blocked
- •Destination Port Blocked, Router Doesn't Respond
- •UDP Stimulus-Response
- •Destination Host Listening on Requested Port
- •Destination Host Not Listening on Requested Port
- •Windows tracert
- •TCPdump of tracert
- •Protocol Benders
- •Active FTP
- •Passive FTP
- •UNIX Traceroute
- •Summary of Expected Behavior and Protocol Benders
- •Abnormal Stimuli
- •Evasion Stimulus, Lack of Response
- •Evil Stimulus, Fatal Response
- •No Stimulus, All Response
- •Unconventional Stimulus, Operating System Identifying Response
- •Bogus "Reserved" TCP Flags
- •Anomalous TCP Flag Combinations
- •No TCP Flags
- •Summary of Abnormal Stimuli
- •Summary
- •Chapter 6. DNS
- •Back to Basics: DNS Theory
- •The Structure of DNS
- •Steppin' Out on the Internet
- •DNS Resolution Process
- •TCPdump Output of Resolution
- •Strange TCPdump Notation
- •Caching: Been There, Done That
- •Reverse Lookups
- •Master and Slave Name Servers
- •Zone Transfers
- •Summary of DNS Theory
- •Using DNS for Reconnaissance
- •The nslookup Command
- •Name That Name Server
- •HINFO: Snooping for Details
- •List Zone Map Information
- •Tainting DNS Responses
- •A Weak Link
- •Cache Poisoning
- •Summary
- •Part II: Traffic Analysis
- •Chapter 7. Packet Dissection Using TCPdump
- •Why Learn to Do Packet Dissection?
- •Sidestep DNS Queries
- •Normal Query
- •Evasive Query
- •Introduction to Packet Dissection Using TCPdump
- •Where Does the IP Stop and the Embedded Protocol Begin?
- •Other Length Fields
- •The IP Datagram Length
- •Increasing the Snaplen
- •Dissecting the Whole Packet
- •Freeware Tools for Packet Dissection
- •Ethereal
- •tcpshow
- •Summary
- •Chapter 8. Examining IP Header Fields
- •Insertion and Evasion Attacks
- •Insertion Attacks
- •Evasion Attacks
- •IP Header Fields
- •IP Version Number
- •Protocol Number
- •The Don't Fragment (DF) Flag
- •The More Fragments (MF) Flag
- •Mapping Using Incomplete Fragments
- •IP Numbers
- •IP Identification Number
- •Time to Live (TTL)
- •Looking at the IP ID and TTL Values Together to Discover Spoofing
- •IP Checksums
- •Summary
- •Chapter 9. Examining Embedded Protocol Header Fields
- •Ports
- •TCP Checksums
- •TCP Sequence Numbers
- •Acknowledgement Numbers
- •TCP Flags
- •TCP Corruption
- •ECN Flag Bits
- •Operating System Fingerprinting
- •Retransmissions
- •Using Retransmissions Against a Hostile Host—LaBrea Tarpit Version 1
- •TCP Window Size
- •LaBrea Version 2
- •Ports
- •UDP Port Scanning
- •UDP Length Field
- •ICMP
- •Type and Code
- •Identification and Sequence Numbers
- •Misuse of ICMP Identification and Sequence Numbers
- •Summary
- •Chapter 10. Real-World Analysis
- •You've Been Hacked!
- •Netbus Scan
- •How Slow Can you Go?
- •RingZero Worm
- •Summary
- •Chapter 11. Mystery Traffic
- •The Event in a Nutshell
- •The Traffic
- •DDoS or Scan
- •Source Hosts
- •Destination Hosts
- •Scanning Rates
- •Fingerprinting Participant Hosts
- •Arriving TTL Values
- •TCP Window Size
- •TCP Options
- •TCP Retries
- •Summary
- •Part III: Filters/Rules for Network Monitoring
- •Chapter 12. Writing TCPdump Filters
- •The Mechanics of Writing TCPdump Filters
- •Bit Masking
- •Preserving and Discarding Individual Bits
- •Creating the Mask
- •Putting It All Together
- •TCPdump IP Filters
- •Detecting Traffic to the Broadcast Addresses
- •Detecting Fragmentation
- •TCPdump UDP Filters
- •TCPdump TCP Filters
- •Filters for Examining TCP Flags
- •Detecting Data on SYN Connections
- •Summary
- •Chapter 13. Introduction to Snort and Snort Rules
- •An Overview of Running Snort
- •Snort Rules
- •Snort Rule Anatomy
- •Rule Header Fields
- •The Action Field
- •The Protocol Field
- •The Source and Destination IP Address Fields
- •The Source and Destination Port Field
- •Direction Indicator
- •Summary
- •Chapter 14. Snort Rules - Part II
- •Format of Snort Options
- •Rule Options
- •Msg Option
- •Logto Option
- •Ttl Option
- •Id Option
- •Dsize Option
- •Sequence Option
- •Acknowledgement Option
- •Itype and Icode Options
- •Flags Option
- •Content Option
- •Offset Option
- •Depth Option
- •Nocase Option
- •Regex Option
- •Session Option
- •Resp Option
- •Tag Option
- •Putting It All Together
- •Summary
- •Part IV: Intrusion Infrastructure
- •Chapter 15. Mitnick Attack
- •Exploiting TCP
- •IP Weaknesses
- •SYN Flooding
- •Covering His Tracks
- •Identifying Trust Relationships
- •Examining Network Traces
- •Setting Up the System Compromise?
- •Detecting the Mitnick Attack
- •Trust Relationship
- •Port Scan
- •Host Scan
- •Connections to Dangerous Ports
- •TCP Wrappers
- •Tripwire
- •Preventing the Mitnick Attack
- •Summary
- •Chapter 16. Architectural Issues
- •Events of Interest
- •Limits to Observation
- •Human Factors Limit Detects
- •Limitations Caused by the Analyst
- •Limitations Caused by the CIRTs
- •Severity
- •Criticality
- •Lethality
- •Countermeasures
- •Calculating Severity
- •Scanning for Trojans
- •Analysis
- •Severity
- •Host Scan Against FTP
- •Analysis
- •Severity
- •Sensor Placement
- •Outside Firewall
- •Sensors Inside Firewall
- •Both Inside and Outside Firewall
- •Analyst Console
- •Faster Console
- •False Positive Management
- •Display Filters
- •Mark as Analyzed
- •Drill Down
- •Correlation
- •Better Reporting
- •Event-Detection Reports
- •Weekly/Monthly Summary Reports
- •Summary
- •Chapter 17. Organizational Issues
- •Organizational Security Model
- •Security Policy
- •Industry Practice for Due Care
- •Security Infrastructure
- •Implementing Priority Countermeasures
- •Periodic Reviews
- •Implementing Incident Handling
- •Defining Risk
- •Risk
- •Accepting the Risk
- •Trojan Version
- •Malicious Connections
- •Mitigating or Reducing the Risk
- •Network Attack
- •Snatch and Run
- •Transferring the Risk
- •Defining the Threat
- •Recognition of Uncertainty
- •Risk Management Is Dollar Driven
- •How Risky Is a Risk?
- •Quantitative Risk Assessment
- •Qualitative Risk Assessments
- •Why They Don't Work
- •Summary
- •Chapter 18. Automated and Manual Response
- •Automated Response
- •Architectural Issues
- •Response at the Internet Connection
- •Internal Firewalls
- •Host-Based Defenses
- •Throttling
- •Drop Connection
- •Shun
- •Proactive Shunning
- •Islanding
- •Reset
- •Honeypot
- •Proxy System
- •Empty System
- •Honeypot Summary
- •Manual Response
- •Containment
- •Freeze the Scene
- •Sample Fax Form
- •On-Site Containment
- •Site Survey
- •System Containment
- •Hot Search
- •Eradication
- •Recovery
- •Lessons Learned
- •Summary
- •Chapter 19. Business Case for Intrusion Detection
- •Part One: Management Issues
- •Bang for the Buck
- •The Expenditure Is Finite
- •Technology Used to Destabilize
- •Network Impacts
- •IDS Behavioral Modification
- •The Policy
- •Part of a Larger Strategy
- •Part Two: Threats and Vulnerabilities
- •Threat Assessment and Analysis
- •Threat Vectors
- •Threat Determination
- •Asset Identification
- •Valuation
- •Vulnerability Analysis
- •Risk Evaluation
- •Part Three: Tradeoffs and Recommended Solution
- •Identify What Is in Place
- •Identify Your Recommendations
- •Identify Options for Countermeasures
- •Cost-Benefit Analysis
- •Follow-On Steps
- •Repeat the Executive Summary
- •Summary
- •Chapter 20. Future Directions
- •Increasing Threat
- •Improved Targeting
- •How the Threat Will Be Manifested
- •Defending Against the Threat
- •Skills Versus Tools
- •Analysts Skill Set
- •Improved Tools
- •Defense in Depth
- •Emerging Techniques
- •Virus Industry Revisited
- •Smart Auditors
- •Summary
- •Part V: Appendixes
- •Appendix A. Exploits and Scans to Apply Exploits
- •False Positives
- •All Response, No Stimulus
- •Scan or Response?
- •SYN Floods
- •Valid SYN Flood
- •False Positive SYN Flood
- •Back Orifice?
- •IMAP Exploits
- •10143 Signature Source Port IMAP
- •111 Signature IMAP
- •Source Port 0, SYN and FIN Set
- •Source Port 65535 and SYN FIN Set
- •DNS Zone Followed by 0, SYN FIN Targeting NFS
- •Scans to Apply Exploits
- •mscan
- •Son of mscan
- •Access Builder?
- •Single Exploit, Portmap
- •rexec
- •Targeting SGI Systems?
- •Discard
- •Weird Web Scans
- •IP-Proto-191
- •Summary
- •Appendix B. Denial of Service
- •Brute-Force Denial-of-Service Traces
- •Smurf
- •Directed Broadcast
- •Echo-Chargen
- •Elegant Kills
- •Teardrop
- •Land Attack
- •We're Doomed
- •nmap
- •Distributed Denial-of-Service Attacks
- •Intro to DDoS
- •DDoS Software
- •Trinoo
- •Stacheldraht
- •Summary
- •Appendix C. Detection of Intelligence Gathering
- •Network and Host Mapping
- •Host Scan Using UDP Echo Requests
- •Netmask-Based Broadcasts
- •Port Scan
- •Scanning for a Particular Port
- •Complex Script, Possible Compromise
- •"Random" Port Scan
- •Database Correlation Report
- •SNMP/ICMP
- •FTP Bounce
- •NetBIOS-Specific Traces
- •A Visit from a Web Server
- •Null Session
- •Stealth Attacks
- •Explicit Stealth Mapping Techniques
- •FIN Scan
- •Inverse Mapping
- •Answers to Domain Queries
- •Answers to Domain Queries, Part 2
- •Fragments, Just Fragments
- •Measuring Response Time
- •Echo Requests
- •Actual DNS Queries
- •Probe on UDP Port 33434
- •3DNS to TCP Port 53
- •Worms as Information Gatherers
- •Pretty Park Worm
- •RingZero
- •Summary
threat. Vulnerabilities are the gateways by which threats manifest themselves.
Defining the Threat
"Umm, I wouldn't go there if I were you". "Why not?"
"Bad things will happen to you if you go there." "What bad things?"
"Bad things."
This is not a compelling scenario, true? Most of us would not be persuaded by it. Imagine giving a similar pitch to management: If you don't fund an intrusion-detection system, bad things will happen to us.
We need to define and quantify bad things:
●What things?
●How bad?
●How likely they are to occur or repeat?
●How do you know?
●What support do you have for your answer?
So for each threat we can define and enumerate, we need to answer these questions.
How Bad—Impact of Threat
In the end, risk is evaluated in terms of money. This is true even if life is lost; in the case of loss of life, it might be a lot of money. For any threat we have defined, we take the value of the assets at risk and multiply that by how exposed they are. This yields the expected loss if we were to get clobbered by the threat. This is called the single loss expectancy (SLE) and the
formula to calculate SLE is as follows:
Asset value x exposure factor = SLE
The exposure factor is an estimate, ranging from 0 percent to 100 percent of our loss of the asset. Consider the following calculation, the threat of a nuclear bomb exploding just above a
small town whose total assets are worth 90 million dollars:
Example Nuclear bomb/small town ($90M x 100% = $90M)
Now let's bring it home. I have already mentioned that when I have conducted vulnerability scans of sites with UNIX computers I have found a number of systems with the tooltalk vulnerability. Can we apply this formula to these? First, we have to define the threat. Suppose we are a Class C site. The threat is a malicious attacker who gains root, exploits any trust models, encrypts the file systems, and holds the computers ransom for $250,000. The attacker scans the net and finds six vulnerable systems. The buffer-overflow attack quickly yields root. After exploiting the trust models of these systems, our attacker is able to root compromise four additional systems and therefore encrypt the disks of 10 UNIX workstations. So when the CEO of your organization comes in to work on Monday, his secretary finds the following in his email
box:
To: John Smith, CEO From: Dark Haqr Subject: Rans0m
I 0wN U L^m3r It wi11 c0st u a kwart3r Mi11i0n t0 g3t ur dAtA b^k.
What is our SLE at this point? We could say $250,000, but it might not be quite that simple. If there were backups, we might be able to restore from backups and just lose a day or two of work. If there aren't backups (please, please ensure there are always backups), we have a
more interesting problem. At this point, we don't actually know if we will ever get the encryption key. The threat is that we will not. So, the value of the assets is the value of the data on these systems, plus the time to rebuild them from scratch, plus the loss from the downtime. How do we calculate the value of the data?
The value of data can be approximated by the burdened labor rate of the people who have been working on the system for the life of the project(s) on the system. To keep the numbers simple, we will consider each of the UNIX systems to be a professional's desktop. They are working on a single project that is two years along and they each make $60k, but their burdened rate (benefits, office space, and so on) is $100k. Ten people at $100k, for two years is $2 million dollars. What is our degree of exposure? It's 100 percent; the files are already encrypted. So, we quickly see that paying the quarter million and keeping our big mouths shut and not involving law enforcement is probably in our best interest. So in this scenario, we pay the money, get the key, and get back to work and everyone is happy. Now, what happens if we
don't fix the vulnerability?
Frequency of Threat—Annualized
Annualized loss expectancy (ALE) occurs when a threat/vulnerability pairing can reasonably be expected to be consummated more than once in a given year. In a brief given to the Joint Computer Security Conference in March 2000, Dr. Gene Schultz postulated this might be an inadequate measurement. Given the nuclear bomb example in our small town, this can't happen; indeed, we drop as many bombs as we want on the town, but we aren't likely to cause any further damage. ALEs fit very well into models such as shoplifting, returns in the mail-order business, and defaults on loans. In a competitive environment (e-business, for example), however, how many ALEs events can you survive? Consider the case of distributed denial of service. If your web storefront is shut down four or five times in a month, some of that business goes to your competition. How do you recover from that? How do ALEs factor into information assurance and intrusion detection?
I mentioned earlier that intrusion-detection technology is easily applied to unauthorized use detection. I also think that this can be a waste of skilled intrusion-detection analysts. But, there is a powerful business argument that says this is a very wise use of the system and personnel. As we work through the following example, note that even though I kept the numbers ridiculously low, we still ended up with some serious money, enough to pay the burdened rate of those entry-level professionals the organization says it can't afford. Use the following formula
to calculate ALE:
SLE x Annualized rate occurrence = Annual loss expectancy
This is nothing more than our SLE times the number of times it could be expected to occur in a year. This is why we ended the encrypted file system example with the question, "What happens if we don't fix the tooltalk vulnerability?" Dark Haqr takes our money, goes out and buys a Beamer, his friends inquire of the means of his sudden fortune, and we get to play the game again.
Let's do a common example: Web surfing on the job rather than working. First, we need to calculate an SLE. Say we have 1,000 employees, 25 percent of which waste an hour per week
surfing:
$50/hr x 250 = $12,500
To calculate the ALE we observe, they do it every week except when on vacation: $12,500 x 50 = $625,000
You can see why an organization might want to leverage its investment in intrusion-detection equipment and personnel to curb unauthorized use. Again, I kept the numbers much lower than what I have observed to be the case at many sites. Also, in the real world, the waste doesn't tend to be spread evenly across employees, but rather is localized in a small number of employees. If these employees can be identified and canned (after all, if they weren't working, they probably aren't really needed), there are a number of potential savings for the organization.