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Virus Analysis

This research paper explores various virus analysis methods, tools, and research issues such as malware detection techniques, anti-detection strategies, and common forms of malware. It delves into integrity checking, static and dynamic AV scanning, and the challenges of detecting polymorphic and metamorphic viruses. The study also covers attacking strategies against integrity checkers, signature-based scanners, behavior monitors, and more.

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Virus Analysis

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  1. Virus Analysis Techniques, Tools, and Research Issues Part I: Introduction Michael Venable Arun Lakhotia University of Louisiana at Lafayette, USA

  2. Introduction to Malware Common Forms of Malware Detection Techniques Anti-Detection Techniques

  3. Common Forms of Malware • Virus • Needs a vector for propagation • Worm • No vector needed • Can spread by: network shares, email, security holes • Trojan horse • Performs unstated and undesirable function • Spyware, adware, logic bomb, backdoors, rootkits

  4. Detection Technologies • Integrity Checking • Static Anti-Virus (AV) Scanners • Signature-based • Strings • Regular expressions • Static behavior analyzer • Dynamic AV Scanners • Behavior Monitors

  5. AV Detection Process ANALYSIS LAB Sample Malicious: yes/no Removal Instructions DESKTOP Clean File Disinfector Infected File Signature File/Message Malicious: yes/no Scanner

  6. Integrity Checking • Compute cryptographic checksums of files • Periodically compare checksum with current checksum • If mismatch, file has been modified

  7. AV Scanners: Static Analysis • Static Analysis • Analyze behavior of program without execution • Detects Properties true for all executions of a program • Examples • Approximation of values • Analyze patterns of system calls

  8. AV Scanners: Signature-based • Extract byte sequences from malware • Search for byte sequence within files • If found, file is infected • Byte sequences may contain wildcards

  9. Signature-Based Scanning • Hex strings from virus variants • 67 33 74 20 73 38 6D 35 20 76 37 61 • 67 36 74 20 73 32 6D 37 20 76 38 61 • 67 39 74 20 73 37 6D 33 20 76 36 61 • Hex string for detecting virus • 67 ?? 74 20 73 ?? 6D ?? 20 76 ?? 61 • ?? = wildcard

  10. AV Scanners: Dynamic Analysis • Monitor a running program to detect malicious behavior • Examples • Intercepting system calls • Analyzing audit trails • Looking at patterns of system calls • Allows examination of only selected testcases

  11. Anti-Detection Techniques • Attacking Integrity Checkers • Attacking Signature-Based Scanners • Polymorphism • Metamorphism • Attacking Static Behavior Analyzer • Obfuscating Calls • Attacking Behavior Monitors • Non-Deterministic behavior • Change behavior when being monitored

  12. Attacking Integrity Checkers • Intercept open() system call • Open a non-infected backup of the file instead • Restore system to original state after attack • Infect system before checksums are computed

  13. Attacking Signature Scanners: Polymorphism • Virus body is encrypted • Decryptor is propagated with virus • Use different encryption keys • Morph decryptor code • Swap registers • Insert garbage instructions • Replace instruction with equivalents • Reorder subroutines

  14. Polymorphism • Detecting polymorphic viruses • Run suspect program in an emulator • Wait until it decrypts • Decrypted code will be identical for various copies • Use signature scanning on decrypted virus body • Challenges • Determining when decryption is complete • Decryptor can determine whether its running in an emulator

  15. Polymorphic Virus • W32.Bugbear.B • Released in June 2003 • Encrypted body with polymorphic decryptor • Spreads via email & shared network drives • Disarms popular anti-virus and firewall applications • Installs key-logger • Installs backdoor for remote access

  16. Attacking Signature Scanners: Metamorphism • Does not have a decryptor • Morph code of the entire virus body • No constant body • signature scanning will not work

  17. Metamorphism • Detecting metamorphic viruses • Run suspect program in an emulator • Analyze behavior while running • Look for changes in file structure • Some viruses modify files in a consistent way • Disassemble and look for virus-like instructions

  18. Metamorphic Virus • Win32.Evol • The Win32.Evol virus appeared in early July, 2000 • Polymorphic operations: • Swaps instructions with equivalents • Inserts junk code between essential instructions

  19. Metamorphic Virus [Szor, 2001] • An early generationc7060F000055 mov dword ptr [esi], 550000Fhc746048BBC5151 mov dword ptr [esi+0004], 5151BCBBh • A later generationBF0F000055 mov edi, 550000Fh893E mov [esi], edi5F pop edi52 push edxB640 mov dh, 40BA8BEC5151 mov edx, 5151EC8Bh53 push ebx8BDA mov ebx, ebx895E04 mov [esi+0004], ebx

  20. Attacking Behavior Monitors • Bypass higher-level system calls • AKA tunneling • Act benign if running in emulator

  21. Summary • Types of malware • Virus, worms, Trojans, adware, spyware, etc. • AV Technologies • Integrity checkers • AV Scanners – Static Dynamic • AV Process • Analyze and extract signatures in lab • Distribute signatures to desktops • Analyze files/messages on desktops • All AV technologies can be attacked

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