Full Report
Written by: Lakshya Mathur Excel-based malware has been around for decades and has been in the limelight in recent years. During the second half of 2020, we saw... The post XLSM Malware with MacroSheets appeared first on McAfee Blog.
Analysis Summary
The provided article describes the nature of XLSM files containing **MacroSheets** used for malware distribution, but it is heavily truncated and mainly consists of navigation links and product information from the McAfee website, rather than detailed technical analysis of a specific malware sample, tool, or TTPs.
Therefore, the summary will focus on the *threat vector* implied by the title: **XLSM Malware utilizing MacroSheets**.
# Tool/Technique: XLSM Malware utilizing MacroSheets
## Overview
This refers to malicious documents utilizing the `.XLSM` (Macro-Enabled Excel Spreadsheet) file format. The key feature exploited is the presence of "MacroSheets," which contain embedded VBA (Visual Basic for Applications) code or macros intended to execute malicious payloads upon the document being opened and macros enabled by the user. This falls under the category of weaponized documents.
## Technical Details
- Type: Attack Vector / Malware Delivery Mechanism
- Platform: Microsoft Office Suite (Primarily Windows/macOS running Excel)
- Capabilities: Execution of embedded, potentially obfuscated code upon user enablement of macros.
- First Seen: While macro-based threats are old, the specific proliferation via XLSM formats is continuous within phishing campaigns.
## MITRE ATT&CK Mapping
This vector primarily covers the initial access and execution phases.
- **TA0001 - Initial Access**
- T1566 - Phishing
- T1566.001 - Spearphishing Attachment (When delivered via email)
- **TA0002 - Execution**
- T1204 - User Execution
- T1204.002 - Malicious File
## Functionality
### Core Capabilities
- **Document Deception:** Using common spreadsheet formats (.XLSM) to appear benign to end-users.
- **Macro Execution:** Encapsulating malicious VBA code within macro functions that trigger on document open events (e.g., `Workbook_Open`).
- **Payload Delivery:** The embedded VBA code typically downloads secondary stages, establishes persistence, or executes system commands.
### Advanced Features
*The provided text does not detail advanced evasion techniques, but typical XLSM malware often employs:*
- **Obfuscation:** Heavily obfuscating VBA code to bypass static analysis.
- **Bypassing Protections:** Checking for sandboxing environments or disabling security software before execution.
## Indicators of Compromise
*Since the article is a general discussion, specific file hashes or C2s are not provided. Indicators are based on the file type and behavior:*
- File Hashes: N/A (Varies per campaign)
- File Names: Documents leveraging social engineering themes (e.g., "Invoice," "Order Confirmation," "Salary Details") ending in `.xlsm`.
- Registry Keys: N/A (Focuses on file execution rather than persistence mechanism in this context)
- Network Indicators: Execution of PowerShell or MSHTA to fetch secondary payloads (Defanged examples: `hxxp://malicious[.]site/payload[.]exe`)
- Behavioral Indicators: Microsoft Excel spawning suspicious child processes like `cmd.exe`, `powershell.exe`, or `wscript.exe`.
## Associated Threat Actors
Threat actors across various Tiers utilize weaponized Office documents, including Ransomware groups, Information Stealers, and state-sponsored APTs.
## Detection Methods
- Signature-based detection: Signatures for known malicious VBA macros or specific VBA functions known to be used in malware development.
- Behavioral detection: Monitoring for suspicious process creation stemming from Office applications (`winword.exe`, `excel.exe`).
- YARA rules: Rules targeting characteristic VBA headers, strings, or function calls indicative of malicious macros.
## Mitigation Strategies
- Prevention measures: Disabling macro execution by default via Group Policy Objects (GPO) or Microsoft Office Trust Center settings.
- Hardening recommendations: Implementing Application Control (e.g., Windows Defender Application Control or AppLocker) to restrict VBA from executing unintended code. Only enabling macros for truly trusted sources.
## Related Tools/Techniques
- DOCM/DOCX files utilizing VBA macros
- Office Document Phishing
- Macroshell (A common technique used within VBA)