CVE-2022-21840
📋 TL;DR
CVE-2022-21840 is a remote code execution vulnerability in Microsoft Office that allows attackers to execute arbitrary code by tricking users into opening specially crafted documents. This affects users of Microsoft Office on Windows systems. Successful exploitation requires user interaction but can lead to full system compromise.
💻 Affected Systems
- Microsoft Office
- Microsoft 365 Apps
- Microsoft Office LTSC 2021
- Microsoft Office 2019
- Microsoft Office 2016
📦 What is this software?
Excel by Microsoft
Excel by Microsoft
Excel by Microsoft
Excel by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office by Microsoft
Office Web Apps by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Attacker gains full control of the victim's system, installs malware, steals credentials, and moves laterally through the network.
Likely Case
Attacker executes malicious code with the victim's privileges, potentially installing ransomware, spyware, or backdoors.
If Mitigated
With proper controls, exploitation is blocked at the perimeter or detected before significant damage occurs.
🎯 Exploit Status
Exploitation requires social engineering to get user to open malicious document. No authentication bypass required beyond user interaction.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: January 2022 security updates
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2022-21840
Restart Required: Yes
Instructions:
1. Open Windows Update settings. 2. Check for updates. 3. Install January 2022 security updates for Microsoft Office. 4. Restart computer if prompted. 5. Verify Office version is updated.
🔧 Temporary Workarounds
Block Office documents from untrusted sources
windowsConfigure Group Policy or registry to block Office documents from untrusted locations
reg add "HKCU\Software\Microsoft\Office\16.0\Word\Security\Trusted Locations" /v "AllowNetworkLocations" /t REG_DWORD /d 0 /f
Enable Protected View
windowsEnsure Protected View is enabled for documents from the internet
🧯 If You Can't Patch
- Implement application whitelisting to block unauthorized Office document execution
- Deploy email filtering to block malicious attachments and enable macro blocking
🔍 How to Verify
Check if Vulnerable:
Check Office version and compare with patched versions from Microsoft advisoryCheck Version:
Open any Office application > File > Account > About [Application]Verify Fix Applied:
Verify Office version is at or above January 2022 security update level📡 Detection & Monitoring
Log Indicators:
- Office application crashes with unusual error codes
- Suspicious child processes spawned from Office applications
- Unusual Office document opening from network locations
Network Indicators:
- Outbound connections from Office processes to suspicious IPs
- DNS requests for known malicious domains from Office processes
SIEM Query:
source="windows" AND (process_name="winword.exe" OR process_name="excel.exe" OR process_name="powerpnt.exe") AND (event_id=1000 OR event_id=1001) AND message="*faulting*"