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.
Tool | Primary Use | Key Features for Imports/Exports |
---|---|---|
PEview | PE File Viewer | Displays detailed information about PE headers, sections, and import/export tables. |
Detect It Easy (DIE) | Malware Scanner & Packer Detector | Identifies packers and provides PE information, including imports and exports. |
IDA Pro | Disassembler & Debugger | Provides comprehensive analysis of imports and exports, along with disassembly of the code that uses them. |
x64dbg/x32dbg | Debugger | Allows 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.
To list the functions and libraries a program requires to execute.
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
Provides a comprehensive overview of the PE file format, including its structure and key components like import and export tables.
Official Microsoft documentation detailing the Portable Executable file format, essential for understanding its internal structure.
A practical blog post explaining the PE file structure with a focus on malware analysis, including import/export tables.
A SANS Institute blog post that delves into PE file analysis for malware reverse engineering, touching upon import and export tables.
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.
A video tutorial demonstrating how to use the PEview tool to examine the import and export tables of PE files.
The official GitHub repository for Detect It Easy (DIE), a popular tool for analyzing PE files, including their import and export sections.
While a book, this chapter excerpt or related online content often covers PE file structure and analysis techniques relevant to IDA Pro users.
An article from Malwarebytes Labs that explains how malware uses Windows API imports and how to analyze them.
A concise explanation of the export table in the context of malware analysis, highlighting its significance.