CVE-2020-16851
📋 TL;DR
This CVE describes a local privilege escalation vulnerability in OneDrive for Windows Desktop where improper symbolic link handling allows an attacker to overwrite files with elevated privileges. Attackers must first gain local access to the system. This affects Windows users running vulnerable versions of OneDrive.
💻 Affected Systems
- Microsoft OneDrive for Windows Desktop
📦 What is this software?
Onedrive by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
An attacker could delete or overwrite critical system files, potentially leading to system instability, data loss, or persistence mechanisms.
Likely Case
Local attackers could escalate privileges to modify files they shouldn't have access to, potentially compromising user data or system integrity.
If Mitigated
With proper patching and least privilege principles, the impact is limited as attackers would need local access and the vulnerability would be closed.
🎯 Exploit Status
Exploitation requires local access and specially crafted symbolic links. No public exploit code has been disclosed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security update released in October 2020
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-16851
Restart Required: Yes
Instructions:
1. Open OneDrive settings. 2. Check for updates. 3. Install available updates. 4. Restart the system if prompted. 5. Verify OneDrive is running the latest version.
🔧 Temporary Workarounds
Disable OneDrive
windowsTemporarily disable OneDrive to prevent exploitation while awaiting patch
Right-click OneDrive icon in system tray > Settings > Unlink this PC
🧯 If You Can't Patch
- Implement strict access controls to limit local user privileges
- Monitor for unusual file modification activities in OneDrive directories
🔍 How to Verify
Check if Vulnerable:
Check OneDrive version in settings. If version predates October 2020 security update, system is vulnerable.Check Version:
Check OneDrive version via: Right-click OneDrive system tray icon > Help & Settings > AboutVerify Fix Applied:
Verify OneDrive version is updated to post-October 2020 release and check Windows Update history for the security patch.📡 Detection & Monitoring
Log Indicators:
- Unusual file modification events in OneDrive directories
- Symbolic link creation in OneDrive paths
Network Indicators:
- No network indicators as this is a local vulnerability
SIEM Query:
EventID 4663 (File system audit) with target OneDrive directories and suspicious user accounts