CVE-2021-27051
📋 TL;DR
CVE-2021-27051 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, typically through the Microsoft Store. Successful exploitation could give attackers control over the affected system.
💻 Affected Systems
- Microsoft HEVC Video Extensions
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining SYSTEM-level privileges, enabling data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Limited user-level compromise on individual workstations, potentially leading to credential theft, lateral movement, or data exfiltration from the affected machine.
If Mitigated
No impact if systems are fully patched or the vulnerable component is removed/disabled.
🎯 Exploit Status
Exploitation requires user interaction to open malicious media files. No publicly available exploit code was identified at disclosure.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Update through Microsoft Store (version varies by release)
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-27051
Restart Required: No
Instructions:
1. Open Microsoft Store. 2. Click 'Library' in bottom left. 3. Click 'Get updates' to update all apps. 4. Alternatively, search for 'HEVC Video Extensions' and update directly. 5. Verify update completed successfully.
🔧 Temporary Workarounds
Uninstall HEVC Video Extensions
windowsRemove the vulnerable component entirely if HEVC video playback is not required
Start > Settings > Apps > Apps & features > Search 'HEVC' > Select 'HEVC Video Extensions' > Uninstall
Disable automatic media file handling
windowsConfigure systems to prompt before opening media files from untrusted sources
🧯 If You Can't Patch
- Implement application whitelisting to prevent execution of unauthorized code
- Deploy email/web filtering to block malicious media files and educate users about suspicious attachments
🔍 How to Verify
Check if Vulnerable:
Check Microsoft Store for HEVC Video Extensions version - vulnerable if not updated after February 2021Check Version:
Get-AppxPackage -Name Microsoft.HEVCVideoExtension* | Select-Object Version, InstallLocationVerify Fix Applied:
Verify HEVC Video Extensions shows as updated in Microsoft Store with recent update date📡 Detection & Monitoring
Log Indicators:
- Windows Event Logs showing HEVC Video Extensions crashes or unexpected process creation
- Microsoft Defender alerts for suspicious media file execution
Network Indicators:
- Outbound connections from media player processes to unexpected destinations
- DNS requests for known malicious domains following media file opening
SIEM Query:
EventID=1000 OR EventID=1001 Source='Application Error' AND ProcessName contains 'HEVC' OR 'VideoExtension'