CVE-2021-27064
📋 TL;DR
This vulnerability allows an attacker to elevate privileges on a system by exploiting a flaw in the Visual Studio Installer. Attackers could gain SYSTEM-level access by tricking a user into running a malicious installer. This affects users running vulnerable versions of Visual Studio Installer on Windows systems.
💻 Affected Systems
- Microsoft Visual Studio Installer
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with SYSTEM-level privileges, allowing installation of malware, data theft, and persistence mechanisms.
Likely Case
Local privilege escalation leading to unauthorized software installation, configuration changes, and lateral movement within the network.
If Mitigated
Limited impact if users have restricted privileges and don't run untrusted installers, though the vulnerability still exists.
🎯 Exploit Status
Exploitation requires user to execute a malicious installer. Proof-of-concept code has been published.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update through Visual Studio Installer or Windows Update
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-27064
Restart Required: Yes
Instructions:
1. Open Visual Studio Installer. 2. Click 'Update' or 'Modify'. 3. Follow prompts to install latest version. 4. Alternatively, apply Windows Update patches for Visual Studio components. 5. Restart system if prompted.
🔧 Temporary Workarounds
Restrict Installer Execution
windowsConfigure AppLocker or Software Restriction Policies to block untrusted installer execution
# Use Group Policy: Computer Configuration > Windows Settings > Security Settings > Application Control Policies > AppLocker
User Privilege Reduction
windowsEnsure users run with standard user privileges, not administrative rights
# Use Group Policy: Computer Configuration > Windows Settings > Security Settings > Local Policies > User Rights Assignment
🧯 If You Can't Patch
- Implement strict application whitelisting to prevent unauthorized installer execution
- Educate users about the risks of running untrusted installer packages and implement phishing awareness training
🔍 How to Verify
Check if Vulnerable:
Check Visual Studio version and compare against patched versions in Microsoft advisory. Vulnerable if running outdated Visual Studio Installer.Check Version:
Open Visual Studio Installer and check version in Help > About, or check installed programs in Control PanelVerify Fix Applied:
Verify Visual Studio Installer has been updated to latest version and no longer exhibits the vulnerability behavior.📡 Detection & Monitoring
Log Indicators:
- Windows Event Logs showing unexpected installer processes running with elevated privileges
- Security logs showing privilege escalation attempts
Network Indicators:
- Unusual outbound connections from systems after installer execution
- Download of suspicious installer packages
SIEM Query:
EventID=4688 AND ProcessName LIKE '%vs_installer%' AND NewProcessName LIKE '%system%' OR ParentProcessName LIKE '%vs_installer%'