Understanding VBScript Malware

VBScript, a scripting language developed by Microsoft, is widely used for automating tasks in Windows. It’s not inherently malicious, but its capabilities make it an attractive tool for cyber attackers to develop malware scripts that can manipulate files, access networks, and steal data without detection.

Why VBScript?

• Integration with Windows: VBScript can interact deeply with the Windows environment, accessing the filesystem, registry, and network resources.
• Ease of Execution: VBScript files can be executed directly on any Windows machine without the need for compilation, making them easy to deploy.
• Deception and Obfuscation: VBScript can be obfuscated to hide its true intent from casual observation and automated analysis tools, making it harder to detect and analyze.

The Challenge of Decoding and Deobfuscating

Malware authors commonly employ obfuscation techniques to mask the true purpose of their VBScript code. This makes the task of malware analysis significantly more challenging but not impossible. Decoding and deobfuscating VBScript malware involves peeling back the layers of obfuscation to reveal the original code, which can then be analyzed to understand its functionality and impact.

Step 1: Initial Assessment and Static Analysis

Static analysis is the first line of defense in the malware analysis process. It involves scrutinizing the VBScript code without executing it, looking for patterns and constructs that are commonly used in malicious scripts.

Key Areas of Focus

• String Concatenation and Encoding: Malicious scripts often contain obfuscated code where the actual harmful payload is hidden within long, convoluted strings of concatenated or encoded data. Look for unusual patterns of string concatenation and methods like Base64, XOR, or custom encoding schemes.
• Suspicious VBScript Functions: Certain VBScript functions are red flags when found in scripts due to their potential for misuse. Functions like ExecuteGlobal, Eval, CreateObject (especially with arguments like "WScript.Shell" or "MSXML2.XMLHTTP"), and obfuscated calls to Run methods indicate potentially harmful intent.
• Commented Code and Junk Code: Malicious scripts may contain large blocks of commented-out code or nonsensical, irrelevant code snippets designed to confuse analysts and automated analysis tools.

Tools and Techniques

Syntax Highlighting Editors

Why Use Them: Syntax highlighting editors make it easier to read the code by coloring different parts of the VBScript syntax. This visual differentiation helps in quickly spotting string literals, function calls, and comments, which could be hiding malicious code.

Recommended Tools:

• Notepad++: A free source code editor which supports VBScript syntax highlighting. It's lightweight and has a plugin ecosystem for extended functionality.
• Visual Studio Code (VS Code): Offers extensive support for various languages, including VBScript, through extensions. It provides advanced code navigation and debugging features.

How to Use:

1. Open the VBScript file in the editor.
2. Use the search feature to find suspicious functions and string patterns.
3. Utilize plugins or extensions that can format or beautify the script for better readability.

Regular Expressions

Why Use Them: Regular expressions (regex) are powerful for searching through text for patterns that match encoded strings, suspicious function calls, and obfuscated code snippets.

Recommended Application:

• Regex101: An online regex testing tool that allows you to write and test your regular expressions against any text. It's useful for crafting expressions that match obfuscated code patterns.
• Built-in Features in Editors: Most advanced text editors and IDEs have built-in support for regex search, allowing you to apply your patterns directly within the tool.

How to Use:

1. Craft a regex pattern that matches common encoding schemes (like Base64) or suspicious VBScript functions.
2. Apply the regex in your editor’s search box or on a site like Regex101 to test it against your script.
3. Iterate on your pattern as needed to improve match accuracy.

Static Analysis Tools

Why Use Them: Static analysis tools can automate the detection of malicious patterns, encoded strings, and suspicious API calls within the VBScript, saving time and improving accuracy.

Recommended Tools:

• FlareVM: A fully customizable, Windows-based security distribution for malware analysis, incident response, and penetration testing. It includes tools capable of static analysis.
• PeStudio: While not specific to VBScript, PeStudio can analyze executables that VBScript might interact with or generate. It highlights suspicious indicators useful in malware analysis.

How to Use:

1. For FlareVM and similar environments, set up your analysis environment following the provided documentation.
2. Use PeStudio to analyze executable files associated with the VBScript malware. Open PeStudio, load the executable, and review the indicators and reports generated.
3. Look for unusual activity or flagged indicators that could relate back to the VBScript’s behavior.

Tips for Effective Use:

• Combine Tools for Comprehensive Analysis: Use a combination of syntax editors, regex, and static analysis tools to cover different aspects of the VBScript. Each tool can reveal different facets of the malware.
• Automate Routine Checks: Where possible, automate the search for common malicious patterns or encoded data to speed up the initial analysis.
• Stay Updated on Malware Trends: Malware techniques evolve, so regularly update your patterns, regexes, and toolsets to match the latest threats.

These tools and techniques provide a solid foundation for the initial assessment and static analysis phase of VBScript malware analysis, aiding in the early detection of potentially malicious scripts.

Step 2: Dynamic Analysis and Execution Monitoring

Dynamic analysis complements static analysis by executing the VBScript in a controlled, isolated environment to observe its behavior. This step is crucial for uncovering the script's actual activities, such as file manipulation, network communication, and registry changes.

Execution in a Sandbox

• Use of Virtual Machines: Run the VBScript in a virtual machine (VM) that mimics a standard user's environment but is isolated from the main network and systems to prevent accidental spread or execution of the malware.
• Sandbox Environments: Utilize sandbox environments designed for malware analysis, which can provide detailed logs of the script's actions, including attempted network connections, changes to the file system, and registry modifications.

Monitoring Tools

Process Monitor (ProcMon)

Why Use It: Process Monitor is an advanced monitoring tool for Windows that shows real-time file system, Registry, and process/thread activity. It's invaluable for understanding how malware interacts with the system.

How to Use:

1. Download and Run: Download ProcMon from the Sysinternals website and run it. No installation is required.
2. Filter Configuration: Upon starting, ProcMon can be overwhelming due to the amount of data it captures. Set up filters to exclude irrelevant processes and focus on the VBScript's actions. For example, you can filter by process name if you know the script’s execution process or by path if you know where the malware operates.
3. Capture Data: Let the VBScript run while ProcMon captures the system calls. Pay attention to file creation, deletion, and registry modifications.
4. Analysis: Use the collected data to analyze the behavior of the script. Look for suspicious activity like unusual file access patterns, modifications to startup registry keys, or creation of unknown files.

Wireshark

Why Use It: Wireshark is a network protocol analyzer that can capture and display the data traveling back and forth on a network in real-time. It's essential for identifying any network-based communication performed by the VBScript malware.

How to Use:

1. Setup and Start Capture: Install Wireshark and start a capture on the network interface connected to the internet. If you’re in a virtual environment, ensure that it’s configured to allow network traffic to pass through to the host machine.
2. Run the Malware: Execute the VBScript malware in your controlled environment while Wireshark is capturing.
3. Filter Traffic: Use Wireshark’s powerful filtering capabilities to isolate traffic generated by the malware. This might involve filtering by IP addresses, protocol types, or port numbers known to be used by the VBScript.
4. Analyze Packets: Examine the captured packets for any data being sent out or received by the malware. Look for DNS queries, HTTP requests, or any other protocol traffic that might indicate C2 communication or data exfiltration.

TCPView

Why Use It: TCPView is a Windows program that shows detailed listings of all TCP and UDP endpoints on your system, including the local and remote addresses and state of TCP connections. It's simpler than Wireshark and useful for quickly spotting unexpected network connections.

How to Use:

1. Download and Open: Like ProcMon, TCPView is part of the Sysinternals suite and doesn’t require installation. Open TCPView before running the malware.
2. Monitor Connections: As the VBScript executes, monitor the TCPView window for new connections. Pay attention to unfamiliar remote addresses or processes that shouldn’t be making network connections.
3. Investigate Suspicious Activity: Use the information from TCPView to investigate suspicious connections further. You can cross-reference with Wireshark captures for more detailed analysis.

Tips for Effective Monitoring:

• Isolate Your Environment: Always run malicious scripts in an isolated environment to prevent accidental network spread or data leakage.
• Document Your Findings: Keep detailed notes of your observations and findings. Screenshots, logs, and exported captures are valuable for documentation and further analysis.
• Cross-Reference Tools: Use the insights gained from one tool to enhance your analysis with another. For example, use process names identified in ProcMon to filter network traffic in Wireshark more effectively.

By leveraging these monitoring tools during the dynamic analysis of VBScript malware, you can gain a comprehensive understanding of its behavior, network communications, and impact on the system.

Step 3: Decoding and Deobfuscating the Code

Decoding and deobfuscating the VBScript involves reversing the techniques used by malware authors to hide their code's true purpose. This step requires a mix of automated tools and manual inspection.

Deobfuscation Techniques

• Automated Deobfuscation Tools: Utilize tools specifically designed for VBScript deobfuscation. These can automatically identify and reverse common encoding and obfuscation techniques.
• Manual Code Analysis: In many cases, manual inspection and modification of the code are necessary. This might involve rewriting the script to replace obfuscated function calls with their plain-text equivalents or manually decoding encoded strings.

Example Deobfuscation Code Snippet

1
2    Dim encodedString, decodedString
3    encodedString = "SGVsbG8sIFdvcmxkIQ==" ' Base64-encoded "Hello, World!"
4    decodedString = DecodeBase64(encodedString)
5    WScript.Echo decodedString
6    
7    Function DecodeBase64(base64String)
8        Dim DM, EL
9        Set DM = CreateObject("Microsoft.XMLDOM")
10        Set EL = DM.createElement("tmp")
11        EL.DataType = "bin.base64"
12        EL.Text = base64String
13        DecodeBase64 = BytesToStr(EL.NodeTypedValue)
14    End Function
15    
16    Function BytesToStr(bytes)
17        Set Stream = CreateObject("ADODB.Stream")
18        Stream.Type = 1 'Binary
19        Stream.Open
20        Stream.Write bytes
21        Stream.Position = 0
22        Stream.Type = 2 'Text
23        Stream.Charset = "utf-8"
24        BytesToStr = Stream.ReadText
25        Stream.Close
26    End Function 
27

This snippet illustrates decoding a Base64-encoded string, a common task in unraveling obfuscated VBScript malware.

Tools for Deobfuscation Techniques

Automated Deobfuscation Tools

Why Use Them: Automated tools can save significant time and effort in the deobfuscation process. They are designed to recognize and reverse common obfuscation patterns automatically.

Recommended Tools:

• ViperMonkey: A VBA macro deobfuscation tool that can also handle some VBScript obfuscations. It simulates the execution of VBScript and VBA macros to reveal the underlying actions without running the actual malicious script.

• De4dot: Primarily a .NET deobfuscator, De4dot can be useful for dealing with VBScript that interacts with or generates .NET assemblies as part of its payload or execution process.

How to Use ViperMonkey:

1. Install ViperMonkey following the instructions on its GitHub page.
2. Run ViperMonkey against the obfuscated VBScript file: vipermonkey yourscript.vbs. The tool attempts to simulate the script’s execution and outputs the deobfuscated actions.
3. Analyze the output for insights into the script’s intended actions and further areas for manual analysis.

Manual Code Analysis

Why Do It: Not all obfuscation techniques can be automatically reversed, especially those that are novel or highly customized. Manual analysis allows for the discovery and understanding of such techniques.

Techniques to Employ:

• Pattern Recognition: Become familiar with common obfuscation patterns (such as string reversal, character substitution, or splitting strings across variables) to quickly identify them in scripts.

• Script Debugging: Use the Windows Script Host’s debugger or editors like VS Code with debugging capabilities to step through the script line by line, watching how variables and functions evolve.

How to Debug with VS Code:

1. Set up your VS Code environment with the appropriate extensions for VBScript.
2. Open the obfuscated VBScript file and set breakpoints on suspicious lines or functions.
3. Use the debugger to step through the execution, paying close attention to variable values and function calls. This process can help identify the real purpose behind obfuscated code segments.

Understanding the Malware Logic

After applying automated tools and manual techniques to deobfuscate the VBScript, it’s crucial to piece together the script’s logic to understand its intent and capabilities.

How to Proceed:

1. Code Mapping: Outline the flow of the deobfuscated script, noting key operations like network calls, file manipulations, and registry changes.
2. Function Analysis: Focus on custom functions and their calls throughout the script. These often encapsulate the core malicious activities.
3. External Interactions: Pay special attention to interactions with the external system or network resources, as these can indicate data exfiltration, command and control communication, or further malware downloads.

By combining automated deobfuscation tools with meticulous manual analysis, analysts can peel away the layers of obfuscation in VBScript malware. This process reveals the underlying malicious intent, guiding the development of effective detection and mitigation strategies.

Step 4: Understanding the Malware’s Intent

Analyzing the deobfuscated script allows security professionals to determine the malware's objectives and mechanisms. This understanding is vital for developing detection signatures, crafting incident response strategies, and mitigating the malware's effects.

Analyzing Network Behavior

Examine any code related to network communications to understand how the malware communicates back to its control server, what data it exfiltrates, and how it receives updates or commands.

Tools to Use:

• Wireshark: A network protocol analyzer that can capture and interactively browse the traffic running on a computer network.

• Fiddler: A free web debugging proxy that logs all HTTP(S) traffic between your computer and the Internet, allowing for the inspection of traffic from malware.

File and Registry Operations

Identify and understand the script's file and registry operations to gauge the malware's impact on the infected system. This includes looking for routines that modify system settings, install additional malicious software, or manipulate user data.

Tools to Use:

• Process Monitor (ProcMon): Part of the Sysinternals Suite, it monitors and logs file system, Registry, and process/thread activity in real-time.

• Regshot: An open-source registry compare utility that takes "before" and "after" snapshots of the system registry and then compares them, showing any changes made.

Persistence Mechanisms

Many VBScript malware scripts include mechanisms to ensure they remain active on the infected system after a reboot. Identifying these mechanisms is crucial for fully removing the malware and restoring system integrity.

Persistence Mechanisms

Many malware scripts are designed to ensure they continue to run after system reboots, often by creating or modifying system startup locations.

Tools to Use:

• Autoruns: Also part of the Sysinternals Suite, it shows you what programs are configured to run during system bootup or login, and when you start various built-in Windows applications.

• Malwarebytes StartupLite: Provides a safe, easy, and efficient way to identify and disable unnecessary startup entries.

How to Use Autoruns:

1. Run Autoruns on a snapshot of the infected system before and after the malware execution.
2. Look for new or suspicious entries in the logon tabs, scheduled tasks, services, and other persistence points.
3. Investigate any unknown or suspicious entries by researching the names and file paths online or analyzing the files in a safe environment.

FAQ Section

Q1: What is VBScript malware? A1: VBScript (Visual Basic Scripting Edition) malware refers to malicious scripts written in VBScript, a scripting language developed by Microsoft. These scripts are designed to execute unauthorized actions on a Windows system, such as spreading viruses, stealing data, or gaining unauthorized access.

Q2: Why is VBScript a popular choice for malware? A2: VBScript is popular among cybercriminals due to its deep integration with the Windows operating system, ease of execution, and ability to be obfuscated. Its capability to automate tasks and manipulate system settings and files makes it a powerful tool for creating malware.

Q3: How can VBScript malware be identified? A3: VBScript malware can often be identified through static analysis, looking for suspicious patterns such as string concatenation, encoded strings, and the use of specific functions like Execute, Eval, and WScript.Shell. Dynamic analysis in a controlled environment can also reveal malicious behaviors.

Q4: What are the main steps in analyzing VBScript malware? A4: The main steps include initial assessment and static analysis, dynamic analysis and execution monitoring, decoding and deobfuscating the code, and understanding the malware's intent through detailed examination of its network behavior, file operations, and registry modifications.

Q5: What tools are essential for VBScript malware analysis? A5: Essential tools include syntax highlighting editors (e.g., Notepad++, VS Code) for static analysis, sandbox environments and network monitoring tools (e.g., Wireshark) for dynamic analysis, and specialized deobfuscation tools (e.g., ViperMonkey) along with debuggers for decoding obfuscated scripts.

Q6: How can one safely analyze VBScript malware? A6: Safe analysis requires conducting the examination within an isolated environment, such as a virtual machine or a dedicated analysis machine, to prevent the malware from affecting the host system or network. Employing sandboxes and using up-to-date analysis tools also contribute to safety.

Q7: What is obfuscation in the context of VBScript malware? A7: Obfuscation refers to techniques used by malware authors to conceal their code’s true purpose. This can include encoding strings, using complex and misleading variable names, and splitting executable code across various parts of the script to evade detection and analysis.

Q8: Can VBScript malware be automatically deobfuscated? A8: While some automated tools can deobfuscate common patterns and techniques, not all obfuscated scripts can be fully decoded automatically due to the variety and complexity of obfuscation methods. Manual analysis often plays a crucial role in understanding deeply obfuscated malware.

Conclusion

Decoding and deobfuscating VBScript malware is a meticulous process that unveils the mechanisms and intents of cyber threats. Through a structured approach and a commitment to cybersecurity, infosec professionals can demystify complex malicious scripts, contributing to the collective defense against digital threats. This guide underscores the importance of expertise, vigilance, and collaboration in the ongoing battle against malware.