CVE-2021-1713
📋 TL;DR
This vulnerability allows remote code execution when Microsoft Excel opens a specially crafted file. Attackers could exploit this to run arbitrary code with the privileges of the current user. Users of affected Microsoft Excel versions are at risk.
💻 Affected Systems
- Microsoft Excel
📦 What is this software?
365 Apps by Microsoft
Excel by Microsoft
Excel by Microsoft
Excel by Microsoft
Office by Microsoft
Office by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise via arbitrary code execution with user privileges, potentially leading to data theft, ransomware deployment, or lateral movement.
Likely Case
Malicious Excel document delivered via phishing leads to malware installation or credential theft on the victim's machine.
If Mitigated
Limited impact due to application sandboxing, user awareness preventing malicious file execution, and network segmentation.
🎯 Exploit Status
Exploitation requires user interaction to open malicious Excel file. No public exploit code available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security updates released January 2021
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-1713
Restart Required: Yes
Instructions:
1. Open Microsoft Excel. 2. Go to File > Account > Update Options > Update Now. 3. Install available updates. 4. Restart computer if prompted.
🔧 Temporary Workarounds
Block Office file types via email filtering
allConfigure email gateways to block or quarantine Excel files from untrusted sources.
Enable Protected View
windowsEnsure Protected View is enabled for files from the internet to prevent automatic macro execution.
🧯 If You Can't Patch
- Implement application whitelisting to prevent unauthorized Excel execution
- Use network segmentation to limit Excel usage to isolated workstations
🔍 How to Verify
Check if Vulnerable:
Check Excel version via File > Account > About Excel. If version is older than January 2021 updates, likely vulnerable.Check Version:
In Excel: File > Account > About ExcelVerify Fix Applied:
Verify Excel has installed January 2021 security updates via File > Account > Update Options > View Updates.📡 Detection & Monitoring
Log Indicators:
- Excel crash logs with memory corruption errors
- Windows Event Logs showing unexpected Excel process termination
Network Indicators:
- Unusual outbound connections from Excel process
- SMB/NTLM authentication attempts from Excel
SIEM Query:
source="windows" AND process="EXCEL.EXE" AND (event_id=1000 OR event_id=1001)