Art of Computer Virus Research and Defense, The

Peter Szor is security architect for Symantec Security Response, where he has been designing and building antivirus technologies for the Norton AntiVirus product line since 1999. From 1990 to 1995, Szor wrote and maintained his own antivirus program, Pasteur. A renowned computer virus and security researcher, Szor speaks frequently at the Virus Bulletin, EICAR, ICSA, and RSA conferences, as well as the USENIX Security Symposium. He currently serves on the advisory board of Virus Bulletin magazine, and is a founding member of the AVED (AntiVirus Emergency Discussion) network. © Copyright Pearson Education. All rights reserved.

About the Author.

Preface.

Acknowledgments.

I. STRATEGIES OF THE ATTACKER.

1. Introduction to the Games of Nature.

    Early Models of Self-Replicating Structures

      John von Neumann: Theory of Self-Reproducing Automata

      Fredkin: Reproducing Structures

      Conway: Game of Life

      Core War: The Fighting Programs

    Genesis of Computer Viruses

    Automated Replicating Code: The Theory and Definition of Computer Viruses

    References

2. The Fascination of Malicious Code Analysis.

    Common Patterns of Virus Research

    Antivirus Defense Development

    Terminology of Malicious Programs

      Viruses

      Worms

      Logic Bombs

      Trojan Horses

      Germs

      Exploits

      Downloaders

      Dialers

      Droppers

      Injectors

      Auto-Rooters

      Kits (Virus Generators)

      Spammer Programs

      Flooders

      Keyloggers

      Rootkits

    Other Categories

      Joke Programs

      Hoaxes: Chain Letters

      Other Pests: Adware and Spyware

    Computer Malware Naming Scheme

     

      ://

      /

      .

     

     

      []

     

      :

      #

      @m or @mm

      !

    Annotated List of Officially Recognized Platform Names

    References

3. Malicious Code Environments.

    Computer Architecture Dependency

    CPU Dependency

    Operating System Dependency

    Operating System Version Dependency

    File System Dependency

      Cluster Viruses

      NTFS Stream Viruses

      NTFS Compression Viruses

      ISO Image Infection

    File Format Dependency

      COM Viruses on DOS

      EXE Viruses on DOS

      NE (New Executable) Viruses on 16-bit Windows and OS/2

      LX Viruses on OS/2

      PE (Portable Executable) Viruses on 32-bit Windows

      ELF (Executable and Linking Format) Viruses on UNIX

      Device Driver Viruses

      Object Code and LIB Viruses

    Interpreted Environment Dependency

      Macro Viruses in Microsoft Products

      REXX Viruses on IBM Systems

      DCL (DEC Command Language) Viruses on DEC/VMS

      Shell Scripts on UNIX (csh, ksh, and bash)

      VBScript (Visual Basic Script) Viruses on Windows Systems

      BATCH Viruses

      Instant Messaging Viruses in mIRC, PIRCH scripts

      SuperLogo Viruses

      JScript Viruses

      Perl Viruses

      WebTV Worms in JellyScript Embedded in HTML Mail

      Python Viruses

      VIM Viruses

      EMACS Viruses

      TCL Viruses

      PHP Viruses

      MapInfo Viruses

      ABAP Viruses on SAP

      Help File Viruses on Windows–When You Press F1…

      JScript Threats in Adobe PDF

      AppleScript Dependency

      ANSI Dependency

      Macromedia Flash ActionScript Threats

      HyperTalk Script Threats

      AutoLisp Script Viruses

      Registry Dependency

      PIF and LNK Dependency

      Lotus Word Pro Macro Viruses

      AmiPro Document Viruses

      Corel Script Viruses

      Lotus 1-2-3 Macro Dependency

      Windows Installation Script Dependency

      AUTORUN.INF and Windows INI File Dependency

      HTML (Hypertext Markup Language) Dependency

    Vulnerability Dependency

    Date and Time Dependency

    JIT Dependency: Microsoft .NET Viruses

    Archive Format Dependency

    File Format Dependency Based on Extension

    Network Protocol Dependency

    Source Code Dependency

      Source Code Trojans

    Resource Dependency on Mac and Palm Platforms

    Host Size Dependency

    Debugger Dependency

      Intended Threats that Rely on a Debugger

    Compiler and Linker Dependency

    Device Translator Layer Dependency

    Embedded Object Insertion Dependency

    Self-Contained Environment Dependency

    Multipartite Viruses

    Conclusion

    References

4. Classification of Infection Strategies.

    Boot Viruses

      Master Boot Record (MBR) Infection Techniques

      DOS BOOT Record (DBR) - Infection Techniques

      Boot Viruses That Work While Windows 95 Is Active

      Possible Boot Image Attacks in Network Environments

    File Infection Techniques

      Overwriting Viruses

      Random Overwriting Viruses

      Appending Viruses

      Prepending Viruses

      Classic Parasitic Viruses

      Cavity Viruses

      Fractionated Cavity Viruses

      Compressing Viruses

      Amoeba Infection Technique

      Embedded Decryptor Technique

      Embedded Decryptor and Virus Body Technique

      Obfuscated Tricky Jump Technique

      Entry-Point Obscuring (EPO) Viruses

      Possible Future Infection Techniques: Code Builders

    An In-Depth Look at Win32 Viruses

      The Win32 API and Platforms That Support It

      Infection Techniques on 32-Bit Windows

      Win32 and Win64 Viruses: Designed for Microsoft Windows?

    Conclusion

    References

5. Classification of In-Memory Strategies.

    Direct-Action Viruses

    Memory-Resident Viruses

      Interrupt Handling and Hooking

      Hook Routines on INT 13h (Boot Viruses)

      Hook Routines on INT 21h (File Viruses)

      Common Memory Installation Techniques Under DOS

      Stealth Viruses

      Disk Cache and System Buffer Infection

    Temporary Memory-Resident Viruses

    Swapping Viruses

    Viruses in Processes (in User Mode)

    Viruses in Kernel Mode (Windows 9x/Me)

    Viruses in Kernel Mode (Windows NT/2000/XP)

    In-Memory Injectors over Networks

    References

6. Basic Self-Protection Strategies.

    Tunneling Viruses

      Memory Scanning for Original Handler

      Tracing with Debug Interfaces

      Code Emulation—Based Tunneling

      Accessing the Disk Using Port I/O

      Using Undocumented Functions

    Armored Viruses

      Antidisassembly

      Encrypted Data

      Code Confusion to Avoid Analysis

      Opcode Mixing—Based Code Confusion

      Using Checksum

      Compressed, Obfuscated Code

      Antidebugging

      Antiheuristics

      Antiemulation Techniques

      Antigoat Viruses

    Aggressive Retroviruses

    References

7. Advanced Code Evolution Techniques and Computer Virus Generator Kits.

    Introduction

    Evolution of Code

    Encrypted Viruses

    Oligomorphic Viruses

    Polymorphic Viruses

      The 1260 Virus

      The Dark Avenger Mutation Engine (MtE)

      32-Bit Polymorphic Viruses

    Metamorphic Viruses

      What Is a Metamorphic Virus?

      Simple Metamorphic Viruses

      More Complex Metamorphic Viruses and Permutation Techniques

      Mutating Other Applications: The Ultimate Virus Generator?

      Advanced Metamorphic Viruses: Zmist

      {W32, Linux}/Simile: A Metamorphic Engine Across Systems

      The Dark Future–MSIL Metamorphic Viruses

    Virus Construction Kits

      VCS (Virus Construction Set)

      GenVir

      VCL (Virus Creation Laboratory)

      PS-MPC (Phalcon-Skism Mass-Produced Code Generator)

      NGVCK (Next Generation Virus Creation Kit)

      Other Kits and Mutators

      How to Test a Virus Construction Tool?

    References

8. Classification According to Payload.

    No-Payload

    Accidentally Destructive Payload

    Nondestructive Payload

    Somewhat Destructive Payload

    Highly Destructive Payload

      Viruses That Overwrite Data

      Data Diddlers

      Viruses That Encrypt Data: The “Good,” the Bad, and the Ugly

      Hardware Destroyers

    DoS (Denial of Service) Attacks

    Data Stealers: Making Money with Viruses

      Phishing Attacks

      Backdoor Features

    Conclusion

    References

9. Strategies of Computer Worms.

    Introduction

    The Generic Structure of Computer Worms

      Target Locator

      Infection Propagator

      Remote Control and Update Interface

      Life-Cycle Manager

      Payload

      Self-Tracking

    Target Locator

      E-Mail Address Harvesting

      Network Share Enumeration Attacks

      Network Scanning and Target Fingerprinting

    Infection Propagators

      Attacking Backdoor-Compromised Systems

      Peer-to-Peer Network Attacks

      Instant Messaging Attacks

      E-Mail Worm Attacks and Deception Techniques

      E-Mail Attachment Inserters

      SMTP Proxy—Based Attacks

      SMTP Attacks

      SMTP Propagation on Steroids Using MX Queries

      NNTP (Network News Transfer Protocol) Attacks

    Common Worm Code Transfer and Execution Techniques

      Executable Code—Based Attacks

      Links to Web Sites or Web Proxies

      HTML-Based Mail

      Remote Login-Based Attacks

      Code Injection Attacks

      Shell Code—Based Attacks

    Update Strategies of Computer Worms

      Authenticated Updates on the Web or Newsgroups

      Backdoor-Based Updates

    Remote Control via Signaling

      Peer-to-Peer Network Control

    Intentional and Accidental Interactions

      Cooperation

      Competition

      The Future: A Simple Worm Communication Protocol?

    Wireless Mobile Worms

    References

10. Exploits, Vulnerabilities, and Buffer Overflow Attacks.

    Introduction

      Definition of Blended Attack

      The Threat

    Background

    Types of Vulnerabilities

      Buffer Overflows

      First-Generation Attacks

      Second-Generation Attacks

      Third-Generation Attacks

    Current and Previous Threats

      The Morris Internet Worm, 1988 (Stack Overflow to Run

 - Shellcode)

      Linux/ADM, 1998 (“Copycatting” the Morris Worm)

      The CodeRed Outbreak, 2001 (The Code Injection Attack)

      Linux/Slapper Worm, 2002 (A Heap Overflow Example)

      W32/Slammer Worm, January 2003 (The Mini Worm)

      Blaster Worm, August 2003 (Shellcode-Based Attack on Win32)

      Generic Buffer Overflow Usage in Computer Viruses

      Description of W32/Badtrans.B@mm

      Exploits in W32/Nimda.A@mm

      Description of W32/Bolzano

      Description of VBS/Bubbleboy

      Description of W32/Blebla

    Summary

    References

II. STRATEGIES OF THE DEFENDER.

11. Antivirus Defense Techniques.

    First-Generation Scanners

      String Scanning

      Wildcards

      Mismatches

      Generic Detection

      Hashing

      Bookmarks

      Top-and-Tail Scanning

      Entry-Point and Fixed-Point Scanning

      Hyperfast Disk Access

    Second-Generation Scanners

      Smart Scanning

      Skeleton Detection

      Nearly Exact Identification

      Exact Identification

    Algorithmic Scanning Methods

      Filtering

      Static Decryptor Detection

      The X-RAY Method

    Code Emulation

      Encrypted and Polymorphic Virus Detection Using Emulation

      Dynamic Decryptor Detection

    Metamorphic Virus Detection Examples

      Geometric Detection

      Disassembling Techniques

      Using Emulators for Tracing

    Heuristic Analysis of 32-Bit Windows Viruses

      Code Execution Starts in the Last Section

      Suspicious Section Characteristics

      Virtual Size Is Incorrect in PE Header

      Possible “Gap” Between Sections

      Suspicious Code Redirection

      Suspicious Code Section Name

      Possible Header Infection

      Suspicious Imports from KERNEL32.DLL by Ordinal

      Import Address Table Is Patched

      Multiple PE Headers

      Multiple Windows Headers and Suspicious KERNEL32.DLL Imports

      Suspicious Relocations

      Kernel Look-Up

      Kernel Inconsistency

      Loading a Section into the VMM Address Space

      Incorrect Size of Code in Header

      Examples of Suspicious Flag Combinations

    Heuristic Analysis Using Neural Networks

    Regular and Generic Disinfection Methods

      Standard Disinfection

      Generic Decryptors

      How Does a Generic Disinfector Work?

      How Can the Disinfector Be Sure That the File Is Infected?

      Where Is the Original End of the Host File?

      How Many Virus Types Can We Handle This Way?

      Examples of Heuristics for Generic Repair

      Generic Disinfection Examples

    Inoculation

    Access Control Systems

    Integrity Checking

      False Positives

      Clean Initial State

      Speed

      Special Objects

      Necessity of Changed Objects

      Possible Solutions

    Behavior Blocking

    Sand-Boxing

    Conclusion

    References

12. Memory Scanning and Disinfection.

    Introduction

    The Windows NT Virtual Memory System

    Virtual Address Spaces

    Memory Scanning in User Mode

      The Secrets of NtQuerySystemInform-ation()

      Common Processes and Special System Rights

      Viruses in the Win32 Subsystem

      Win32 Viruses That Allocate Private Pages

      Native Windows NT Service Viruses

      Win32 Viruses That Use a Hidden Window Procedure

      Win32 Viruses That Are Part of the Executed Image Itself

    Memory Scanning and Paging

      Enumerating Processes and Scanning File Images

    Memory Disinfection

      Terminating a Particular Process That Contains Virus Code

      Detecting and Terminating Virus Threads

      Patching the Virus Code in the Active Pages

      How to Disinfect Loaded DLLs and Running Applications

    Memory Scanning in Kernel Mode

      Scanning the User Address Space of Processes

      Determining NT Service API Entry Points

      Important NT Functions for Kernel-Mode Memory Scanning

      Process Context

      Scanning the Upper 2GB of Address Space

      How Can You Deactivate a Filter Driver Virus?

      Dealing with Read-Only Kernel Memory

      Kernel-Mode Memory Scanning on 64-Bit Platforms

    Possible Attacks Against Memory Scanning

    Conclusion and Future Work

    References

13. Worm-Blocking Techniques and Host-Based Intrusion Prevention.

    Introduction

      Script Blocking and SMTP Worm Blocking

      New Attacks to Block: CodeRed, Slammer

    Techniques to Block Buffer Overflow Attacks

      Code Reviews

      Compiler-Level Solutions

      Operating System-Level Solutions and Run-Time Extensions

      Subsystem Extensions–Libsafe

      Kernel Mode Extensions

      Program Shepherding

    Worm-Blocking Techniques

      Injected Code Detection

      Send Blocking: An Example of Blocking Self-Sending Code

      Exception Handler Validation

      Other Return-to-LIBC Attack Mitigation Techniques

      “GOT” and “IAT” Page Attributes

      High Number of Connections and Connection Errors

    Possible Future Worm Attacks

      A Possible Increase of Retroworms

      “Slow” Worms Below the Radar

      Polymorphic and Metamorphic Worms

      Largescale Damage

      Automated Exploit Discovery–Learning from the Environment

    Conclusion

    References

14. Network-Level Defense Strategies.

    Introduction

    Using Router Access Lists

    Firewall Protection

    Network-Intrusion Detection Systems

    Honeypot Systems

    Counterattacks

    Early Warning Systems

    Worm Behavior Patterns on the Network

      Capturing the Blaster Worm

      Capturing the Linux/Slapper Worm

      Capturing the W32/Sasser.D Worm

      Capturing the Ping Requests of the W32/Welchia Worm

      Detecting W32/Slammer and Related Exploits

    Conclusion

    References

15. Malicious Code Analysis Techniques.

    Your Personal Virus Analysis Laboratory

      How to Get the Software?

    Information, Information, Information

      Architecture Guides

      Knowledge Base

    Dedicated Virus Analysis on VMWARE

    The Process of Computer Virus Analysis

      Preparation

      Unpacking

      Disassembling and Decryption

      Dynamic Analysis Techniques

    Maintaining a Malicious Code Collection

    Automated Analysis: The Digital Immune System

    References

16. Conclusion.

    Further Reading

      Information on Security and Early Warnings

      Security Updates

      Computer Worm Outbreak Statistics

      Computer Virus Research Papers

      Contact Information for Antivirus Vendors

      Antivirus Testers and Related Sites

Index.