Practical Malware Analysis: Ch 0: Malware Analysis Primer & 1: Basic Static Techniques
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This document provides an overview of basic static malware analysis techniques. It discusses using antivirus scanners, hashing files, and finding strings to identify malware without executing it. It also covers analyzing the Portable Executable (PE) file format used in Windows executables, including examining the PE header, imported and exported functions, linked libraries, and sections like .text and .rsrc. The document demonstrates various tools for these static analysis tasks like HashCalc, strings, PEview, Dependency Walker, and Resource Hacker.
Practical Malware Analysis: Ch 0: Malware Analysis Primer & 1: Basic Static Techniques
- 1. Practical Malware Analysis Ch 1: Malware Analysis Primer
- 2. The Goals of Malware Analysis
- 3. Incident Response • Case history – A medical clinic with 10 offices found malware on one of their workstations – Hired a consultant to clean & re-image that machine • All done—case closed?
- 4. Incident Response • After malware is found, you need to know – Did an attacker implant a rootkit or trojan on your systems? – Is the attacker really gone? – What did the attacker steal or add? – How did the attack get in • Root-cause analysis
- 5. • Link Ch 1a
- 6. Malware Analysis • Dissecting malware to understand – How it works – How to identify it – How to defeat or eliminate it • A critical part of incident response
- 7. The Goals of Malware Analysis • Information required to respond to a network intrusion – Exactly what happened – Ensure you’ve located all infected machines and files – How to measure and contain the damage – Find signatures for intrusion detection systems
- 8. Signatures • Host-based signatures – Identify files or registry keys on a victim computer that indicate an infection – Focus on what the malware did to the system, not the malware itself • Different from antivirus signature • Network signatures – Detect malware by analyzing network traffic – More effective when made using malware analysis
- 11. Static v. Dynamic Analysis • Static Analysis – Examines malware without running it – Tools: VirusTotal, strings, a disassembler like IDA Pro • Dynamic Analysis – Run the malware and monitor its effect – Use a virtual machine and take snapshots – Tools: RegShot, Process Monitor, Process Hacker, CaptureBAT – RAM Analysis: Mandant Redline and Volatility
- 12. Basic Analysis • Basic static analysis – View malware without looking at instructions – Tools: VirusTotal, strings – Quick and easy but fails for advanced malware and can miss important behavior • Basic dynamic analysis – Easy but requires a safe test environment – Not effective on all malware
- 13. Advanced Analysis • Advanced static analysis – Reverse-engineering with a disassembler – Complex, requires understanding of assembly code • Advanced Dynamic Analysis – Run code in a debugger – Examines internal state of a running malicious executable
- 14. Types of Malware
- 15. Types of Malware • Backdoor – Allows attacker to control the system • Botnet – All infected computers receive instructions from the same Command-and-Control (C&C) server • Downloader – Malicious code that exists only to download other malicious code – Used when attacker first gains access
- 16. Types of Malware • Information-stealing malware – Sniffers, keyloggers, password hash grabbers • Launcher – Malicious program used to launch other malicious programs – Often uses nontraditional techniques to ensure stealth or greater access to a system • Rootkit – Malware that conceals the existence of other code – Usually paired with a backdoor
- 17. Types of Malware • Scareware – Frightens user into buying something – Link Ch 1b
- 18. Types of Malware • Spam-sending malware – Attacker rents machine to spammers • Worms or viruses – Malicious code that can copy itself and infect additional computers
- 19. Mass v. Targeted Malware • Mass malware – Intended to infect as many machines as possible – Most common type • Targeted malware – Tailored to a specific target – Very difficult to detect, prevent, and remove – Requires advanced analysis – Ex: Stuxnet
- 20. General Rules for Malware Analysis
- 21. General Rules for Malware Analysis • Don’t Get Caught in Details – You don’t need to understand 100% of the code – Focus on key features • Try Several Tools – If one tool fails, try another – Don’t get stuck on a hard issue, move along • Malware authors are constantly raising the bar
- 22. Ch 2: Basic Static Analysis
- 23. Techniques • Antivirus scanning • Hashes • A file’s strings, functions, and headers
- 25. Only a First Step • Malware can easily change its signature and fool the antivirus • VirusTotal is convenient, but using it may alert attackers that they’ve been caught – Link Ch 2a
- 26. Hashing A fingerprint for malware
- 27. Hashes • MD5 or SHA-1 • Condenses a file of any size down to a fixed- length fingerprint • Uniquely identifies a file well in practice – There are MD5 collisions but they are not common – Collision: two different files with the same hash
- 28. HashCalc
- 29. Hash Uses • Label a malware file • Share the hash with other analysts to identify malware • Search the hash online to see if someone else has already identified the file
- 30. Finding Strings
- 31. Strings • Any sequence of printable characters is a string • Strings are terminated by a null (0x00) • ASCII characters are 8 bits long – Now called ANSI • Unicode characters are 16 bits long – Microsoft calls them "wide characters"
- 33. The strings Command • Native in Linux, also available for Windows • Finds all strings in a file 3 or more characters long
- 34. The strings Command • Bold items can be ignored • GetLayout and SetLayout are Windows functions • GDI32.DLL is a Dynamic Link Library
- 35. Packed and Obfuscated Malware
- 36. Packing Files • The code is compressed, like a Zip file • This makes the strings and instructions unreadable • All you'll see is the wrapper – small code that unpacks the file when it is run
- 37. Detecting Packers with PEiD
- 38. Demo: UPX
- 41. Portable Executable File Format EXE Files
- 42. PE Files • Used by Windows executable files, object code, and DLLs • A data structure that contains the information necessary for Windows to load the file • Almost every file executed on Windows is in PE format
- 43. PE Header • Information about the code • Type of application • Required library functions • Space requirements
- 44. LordPE Demo
- 45. Main Sections
- 46. There are a lot more sections • But the main ones are enough for now • Link Ch 2c
- 47. Linked Libraries and Functions
- 48. Imports • Functions used by a program that are stored in a different program, such as library • Connected to the main EXE by Linking • Can be linked three ways – Statically – At Runtime – Dynamically
- 49. Static Linking • Rarely used for Windows executables • Common in Unix and Linux • All code from the library is copied into the executable • Makes executable large in size
- 50. Runtime Linking • Unpopular in friendly programs • Common in malware, especially packed or obfuscated malware • Connect to libraries only when needed, not when the program starts • Most commonly done with the LoadLibrary and GetProcAddress functions
- 51. Dynamic Linking • Most common method • Host OS searches for necessary libraries when the program is loaded
- 52. Clues in Libraries • The PE header lists every library and function that will be loaded • Their names can reveal what the program does • URLDownloadToFile indicates that the program downloads something
- 54. Shows Dynamically Linked Functions • Normal programs have a lot of DLLs • Malware often has very few DLLs
- 55. Services.exe
- 60. Exports • DLLs export functions • EXEs import functions • Both exports and imports are listed in the PE header • The book says exports are rare in EXEs, but I see a ton of exports in innocent EXEs
- 61. Example: Keylogger • Imports User32.dll and uses the function SetWindowsHookEx which is a popular way keyloggers receive keyboard inputs • It exports LowLevelKeyboardProc and LowLevelMouseProc to send the data elsewhere • It uses RegisterHotKey to define a special keystroke like Ctrl+Shift+P to harvest the collected data
- 62. Ex: A Packed Program • Very few functions • All you see is the unpacker
- 63. The PE File Headers and Sections
- 64. Important PE Sections • .text -- instructions for the CPU to execute • .rdata -- imports & exports • .data – global data • .rsrc – strings, icons, images, menus
- 65. PEView (Link Ch 2e)
- 66. Time Date Stamp • Shows when this executable was compiled • Older programs are more likely to be known to antivirus software • But sometimes the date is wrong – All Delphi programs show June 19, 1992 – Date can also be faked
- 67. IMAGE_SECTION_HEADER • Virtual Size – RAM • Size of Raw Data – DISK • For .text section, normally equal, or nearly equal • Packed executables show Virtual Size much larger than Size of Raw Data for .text section
- 68. Not Packed
- 70. Resource Hacker • Lets you browse the .rsrc section • Strings, icons, and menus • Link Ch 2f
- 71. Resource Hacker in Windows XP
- 72. Resource Hacker in Windows 7