CVE-2021-27049
📋 TL;DR
CVE-2021-27049 is a remote code execution vulnerability in Microsoft's HEVC Video Extensions that allows attackers to execute arbitrary code by tricking users into opening specially crafted media files. This affects Windows systems with the HEVC Video Extensions installed. Attackers could gain the same user rights as the current user.
💻 Affected Systems
- Microsoft HEVC Video Extensions
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining SYSTEM privileges, installing malware, stealing data, and creating persistent backdoors.
Likely Case
Attacker gains user-level privileges to execute code, install ransomware, or steal sensitive files accessible to the user account.
If Mitigated
Limited impact due to patched systems, restricted user privileges, and application whitelisting preventing malicious code execution.
🎯 Exploit Status
Requires user interaction to open malicious media file. No publicly available exploit code as of analysis.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: HEVC Video Extensions version 1.0.41881.0 or later
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-27049
Restart Required: No
Instructions:
1. Open Microsoft Store. 2. Click on 'Library' or 'Downloads and updates'. 3. Check for updates for HEVC Video Extensions. 4. Install available updates. 5. Alternatively, update through Windows Update for systems with automatic updates enabled.
🔧 Temporary Workarounds
Uninstall HEVC Video Extensions
windowsRemove the vulnerable component entirely if not needed for business operations
Get-AppxPackage *HEVCVideoExtension* | Remove-AppxPackage
Restrict media file execution
windowsUse application control policies to block execution of media files from untrusted sources
🧯 If You Can't Patch
- Implement application whitelisting to prevent execution of unauthorized code
- Restrict user privileges to standard user accounts (not administrator)
🔍 How to Verify
Check if Vulnerable:
Check HEVC Video Extensions version in Microsoft Store or via PowerShell: Get-AppxPackage *HEVCVideoExtension* | Select VersionCheck Version:
Get-AppxPackage *HEVCVideoExtension* | Select Name, VersionVerify Fix Applied:
Verify version is 1.0.41881.0 or higher using same PowerShell command📡 Detection & Monitoring
Log Indicators:
- Windows Event Logs showing crashes in HEVCVideoExtension.exe
- Application logs showing unexpected media file processing
Network Indicators:
- Unusual outbound connections after media file processing
- Downloads of suspicious media files
SIEM Query:
EventID=1000 AND Source='Application Error' AND ProcessName='HEVCVideoExtension.exe'