Advanced Malware Analysis: String Analysis and Resource Extraction

In the realm of advanced malware analysis, understanding the internal components of a malicious executable is paramount. String analysis and resource extraction are foundational techniques that provide crucial insights into a malware's functionality, communication methods, and potential targets. This module delves into these techniques, essential for professionals aiming for certifications like the SANS GIAC Security Expert (GSE).

String Analysis: Unveiling Hidden Clues

Strings are sequences of characters embedded within an executable file. They can represent a wide array of information, including file paths, URLs, IP addresses, registry keys, error messages, configuration parameters, and even embedded commands or scripts. Analyzing these strings can quickly reveal a malware's intent and operational characteristics without needing to delve into complex disassembly.

What are some common types of information that can be found within strings in a malware executable?

File paths, URLs, IP addresses, registry keys, error messages, configuration parameters, embedded commands, and scripts.

Tools for String Analysis

Several powerful tools are available to perform string analysis. The choice of tool often depends on the operating system and the specific requirements of the analysis.

Tool	Platform	Key Features
Strings (Sysinternals)	Windows	Extracts ASCII and Unicode strings, customizable search.
FLOSS (FireEye Labs Obfuscated String Solver)	Windows, Linux, macOS	Identifies and decodes obfuscated strings, supports various decoding algorithms.
radare2/rizin	Cross-platform	Powerful reverse engineering framework with robust string extraction capabilities.
objdump	Linux/Unix	Part of GNU Binutils, can display section contents, including strings.

Resource Extraction: Accessing Embedded Components

Many executables, especially those developed for Windows, embed additional resources. These resources can include icons, dialog boxes, cursors, menus, and importantly for malware analysis, embedded files or DLLs. Extracting these resources can reveal secondary payloads, configuration files, or components that the malware dynamically loads.

The Portable Executable (PE) file format, common on Windows, organizes data into sections. One of these sections is the 'Resource Section'. This section contains a hierarchical structure of resources, each identified by a type (e.g., 'RT_RCDATA', 'RT_ICON'), an ID (or name), and a language. Malware often stores encrypted configuration data or secondary payloads within this section, typically under the 'RT_RCDATA' type. Extracting these resources involves parsing the PE header to locate the resource directory table, navigating through the directory entries to find the desired resource, and then extracting its raw data. This process is analogous to opening a nested set of boxes to find a hidden item.

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Text-based content

Library pages focus on text content

Tools for Resource Extraction

Specialized tools are designed to efficiently extract resources from PE files.

When analyzing embedded resources, always consider the possibility of them being encrypted or packed. Further analysis might be required to decrypt or unpack them before they can be understood.

Tool	Platform	Key Features
Resource Hacker	Windows	View, extract, and modify resources. Supports many resource types.
PE Explorer	Windows	Advanced PE file editor with robust resource extraction capabilities.
Exeinfo PE	Windows	Identifies packers, compilers, and can often extract embedded resources.
pestudio	Windows	Comprehensive PE analysis tool that includes resource extraction and analysis.

Advanced Considerations and Next Steps

While string and resource analysis provide a quick overview, advanced malware often employs obfuscation techniques to hide these clues. Understanding these obfuscation methods, such as string encryption, packing, and anti-analysis tricks, is crucial for a thorough analysis. The extracted strings or resources might also require further dynamic analysis or deobfuscation to reveal their true nature.

What is a common resource type used by malware authors to embed encrypted configuration data or secondary payloads?

RT_RCDATA

Learning Resources

Strings (Sysinternals) - Microsoft Docs(documentation)

Official documentation for the Sysinternals Strings utility, a powerful tool for extracting strings from binary files on Windows.

FLOSS (FireEye Labs Obfuscated String Solver)(documentation)

The GitHub repository for FLOSS, which helps reverse engineers discover and decode obfuscated strings in malware.

Resource Hacker(documentation)

A freeware utility to view, extract, modify, and recompile resources for 32-bit and 64-bit Windows executables.

PE Explorer - Resource Editor(documentation)

Information about PE Explorer's resource editor, a comprehensive tool for analyzing and manipulating PE file resources.

Malware Analysis: Strings and Resources - Malwarebytes Labs(blog)

A blog post from Malwarebytes Labs discussing the importance and techniques of analyzing strings and resources in malware.

Reverse Engineering Malware: String Analysis(video)

A YouTube video tutorial demonstrating string analysis techniques in the context of malware reverse engineering.

Understanding the PE File Format - Microsoft Docs(documentation)

Detailed documentation on the Portable Executable (PE) file format, crucial for understanding resource structures.

radare2 Book - Strings(documentation)

Documentation on how to use radare2, a powerful reverse engineering framework, for string analysis.

pestudio - Malware Analysis Tool(documentation)

Information about pestudio, a tool that performs static analysis of executables, including resource extraction and analysis.

Practical Malware Analysis - Chapter 3: Strings(paper)

While a book, Chapter 3 of 'Practical Malware Analysis' is a seminal resource on string analysis in malware, often cited and foundational for this topic.