LibraryImport/Export Table Analysis

Import/Export Table Analysis

Learn about Import/Export Table Analysis as part of SANS GIAC Security Expert (GSE) Certification

Import/Export Table Analysis: Unveiling Malware Functionality

In the realm of malware analysis and reverse engineering, understanding the Import and Export tables of Portable Executable (PE) files is crucial. These tables act as a roadmap, revealing the functions a program relies on (imports) and the functions it makes available to other programs (exports). For advanced certifications like SANS GIAC Security Expert (GSE), mastering this analysis is a fundamental skill.

Understanding PE File Structure

Before diving into import/export tables, it's essential to grasp the basics of the Portable Executable (PE) file format. This format is used for executables, DLLs, and other files on Windows. Key components include the DOS header, PE header, section table, and various data directories, one of which points to the Import Directory.

The Export Table: What a Program Offers

While most malware analysis focuses on imports, understanding exports is equally important, especially for libraries or components designed to be used by other processes. The Export Table details the functions that a PE file makes available to other executables or DLLs.

Tools for Analysis

Several powerful tools can assist in analyzing import and export tables. These tools parse the PE structure and present the information in a human-readable format, saving significant manual effort.

ToolPrimary UseKey Features for Imports/Exports
PEviewPE File ViewerDisplays detailed information about PE headers, sections, and import/export tables.
Detect It Easy (DIE)Malware Scanner & Packer DetectorIdentifies packers and provides PE information, including imports and exports.
IDA ProDisassembler & DebuggerProvides comprehensive analysis of imports and exports, along with disassembly of the code that uses them.
x64dbg/x32dbgDebuggerAllows dynamic analysis, showing resolved imports and function calls during runtime.

Practical Application in Malware Analysis

When encountering a new malware sample, the first step is often to examine its import table. This provides immediate clues about its capabilities. For example:

A malware sample that imports functions like InternetOpen, HttpSendRequest, and CreateProcess strongly suggests network communication capabilities and the ability to launch other processes, potentially for downloading additional payloads or spreading.

Similarly, analyzing the export table of a suspicious DLL can reveal its intended role. If a DLL exports functions that perform system modifications or data exfiltration, it's a significant indicator of malicious design.

Advanced Considerations for GSE

For the GSE certification, simply listing imports and exports is insufficient. Advanced analysis involves:

  • Resolving IAT (Import Address Table) entries: Understanding how the loader populates the IAT and how malware might manipulate it.
  • Identifying API hashing: Malware often obfuscates API calls by hashing function names and looking them up at runtime. Recognizing these patterns is key.
  • Analyzing delayed imports: Some malware uses delayed imports to evade static analysis.
  • Understanding ordinal imports: Recognizing when functions are imported by ordinal rather than by name, which can be a sign of packing or obfuscation.
  • Correlating imports with code: Linking imported functions to the actual code that calls them within the disassembled binary.
What is the primary purpose of the Import Table in a PE file?

To list the functions and libraries a program requires to execute.

What does the Export Table of a DLL indicate?

The functions and data that the DLL makes available for other programs to use.

Conclusion

Mastering import and export table analysis is a cornerstone of effective malware reverse engineering. It provides a high-level understanding of a program's functionality and dependencies, guiding deeper analysis and aiding in the identification of malicious activities. For aspiring GSEs, this skill is not just beneficial, but essential.

Learning Resources

Portable Executable (PE) File Format - Wikipedia(wikipedia)

Provides a comprehensive overview of the PE file format, including its structure and key components like import and export tables.

Understanding the PE File Format - Microsoft Docs(documentation)

Official Microsoft documentation detailing the Portable Executable file format, essential for understanding its internal structure.

Malware Analysis: PE File Structure - MalwareTech(blog)

A practical blog post explaining the PE file structure with a focus on malware analysis, including import/export tables.

Reverse Engineering Malware: PE File Analysis - SANS Institute(blog)

A SANS Institute blog post that delves into PE file analysis for malware reverse engineering, touching upon import and export tables.

Practical Malware Analysis - Chapter 3: Portable Executable (PE) Files(book_chapter)

This chapter from the renowned 'Practical Malware Analysis' book provides in-depth coverage of PE file structure, including detailed explanations of import and export tables.

Analyzing PE Files with PEview - YouTube(video)

A video tutorial demonstrating how to use the PEview tool to examine the import and export tables of PE files.

Detect It Easy (DIE) - GitHub(documentation)

The official GitHub repository for Detect It Easy (DIE), a popular tool for analyzing PE files, including their import and export sections.

IDA Pro Book: Chapter 2 - The PE File Format(book_chapter)

While a book, this chapter excerpt or related online content often covers PE file structure and analysis techniques relevant to IDA Pro users.

Understanding Windows API Imports - Malwarebytes Labs(blog)

An article from Malwarebytes Labs that explains how malware uses Windows API imports and how to analyze them.

Export Table - Malware Analysis Wiki(blog)

A concise explanation of the export table in the context of malware analysis, highlighting its significance.