CVE-2021-28453
📋 TL;DR
CVE-2021-28453 is a remote code execution vulnerability in Microsoft Word that allows attackers to execute arbitrary code by tricking users into opening specially crafted documents. This affects users of Microsoft Word on Windows systems. Successful exploitation requires user interaction but can lead to full system compromise.
💻 Affected Systems
- Microsoft Word
- Microsoft Office
📦 What is this software?
365 Apps by Microsoft
Office by Microsoft
Office by Microsoft
Office Web Apps by Microsoft
Word by Microsoft
Word by Microsoft
Word by Microsoft
Word by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete system takeover with attacker gaining the same privileges as the logged-in user, potentially leading to data theft, ransomware deployment, or lateral movement within the network.
Likely Case
Malware installation leading to data exfiltration, credential theft, or persistence mechanisms being established on the compromised system.
If Mitigated
Limited impact with proper application sandboxing and user privilege restrictions, potentially resulting in application crash but no code execution.
🎯 Exploit Status
Exploitation requires user interaction to open malicious document. Proof-of-concept code has been publicly disclosed. The vulnerability has been actively exploited in targeted attacks.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security updates released in May 2021 (KB5001342 for Office 2016, KB5001347 for Office 2019)
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-28453
Restart Required: Yes
Instructions:
1. Open Microsoft Word. 2. Go to File > Account > Update Options > Update Now. 3. Alternatively, download and install the May 2021 security updates from Microsoft Update Catalog. 4. Restart the system after installation.
🔧 Temporary Workarounds
Disable Protected View for Internet files
windowsConfigure Word to open files from the Internet in Protected View to prevent automatic code execution
Set-ItemProperty -Path "HKCU:\Software\Microsoft\Office\16.0\Word\Security" -Name "ProtectedView" -Value 1
Block Office macros from the Internet
windowsPrevent Office from running macros in documents downloaded from the Internet
Set-ItemProperty -Path "HKCU:\Software\Microsoft\Office\16.0\Word\Security" -Name "BlockInternetMacros" -Value 1
🧯 If You Can't Patch
- Implement application whitelisting to prevent unauthorized executables from running
- Use Microsoft Office Viewer or web-based Office applications to open untrusted documents
🔍 How to Verify
Check if Vulnerable:
Check Word version in File > Account > About Word. If version is older than May 2021 updates, system is vulnerable.Check Version:
powershell "Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*' | Where-Object {$_.DisplayName -like '*Word*'} | Select-Object DisplayName, DisplayVersion"Verify Fix Applied:
Verify Word version shows May 2021 or later updates installed. Check Windows Update history for KB5001342 or KB5001347.📡 Detection & Monitoring
Log Indicators:
- Word process spawning unexpected child processes
- Unusual Office document opening events from untrusted sources
- Windows Event Log ID 4688 with Word as parent process
Network Indicators:
- Outbound connections from Word process to suspicious IPs
- DNS queries for command and control domains from Office processes
SIEM Query:
source="windows" (process_name="WINWORD.EXE" AND child_process!="explorer.exe") OR (event_id=4688 AND parent_process_name="WINWORD.EXE")