CVE-2021-28465
📋 TL;DR
CVE-2021-28465 is a remote code execution vulnerability in Microsoft Web Media Extensions that allows attackers to execute arbitrary code on affected systems by tricking users into opening specially crafted media files. This affects Windows systems with the Web Media Extensions component installed, primarily impacting media playback applications. Attackers could gain the same user rights as the current user, potentially leading to system compromise.
💻 Affected Systems
- Microsoft Web Media Extensions
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining SYSTEM privileges, installing malware, stealing data, and creating persistent backdoors.
Likely Case
Attacker gains user-level privileges, executes malicious code, and potentially escalates privileges to compromise the entire system.
If Mitigated
Limited impact due to application sandboxing, user account control, and network segmentation preventing lateral movement.
🎯 Exploit Status
Exploitation requires user interaction to open malicious media file. Multiple proof-of-concepts exist in security research community.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security updates released in May 2021
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-28465
Restart Required: Yes
Instructions:
1. Apply May 2021 Windows security updates via Windows Update. 2. For enterprise: Deploy through WSUS or Microsoft Endpoint Configuration Manager. 3. Verify update KB5003173 or later is installed.
🔧 Temporary Workarounds
Disable Web Media Extensions
windowsRemove or disable the Web Media Extensions component to prevent exploitation
Remove-AppxPackage Microsoft.WebMediaExtensions
Restrict media file execution
windowsConfigure application control policies to block untrusted media files
🧯 If You Can't Patch
- Implement application whitelisting to prevent execution of unauthorized media players
- Use network segmentation to isolate systems and limit lateral movement potential
🔍 How to Verify
Check if Vulnerable:
Check if Web Media Extensions is installed and if May 2021 security updates are missingCheck Version:
Get-AppxPackage Microsoft.WebMediaExtensions | Select VersionVerify Fix Applied:
Verify KB5003173 or later security update is installed via 'wmic qfe list' or Settings > Update & Security📡 Detection & Monitoring
Log Indicators:
- Unexpected media file execution events
- Process creation from media players with suspicious parameters
- Windows Event Logs showing Web Media Extensions crashes
Network Indicators:
- Outbound connections from media players to suspicious IPs
- Unusual network traffic following media file execution
SIEM Query:
EventID=4688 AND (ProcessName LIKE '%wmplayer%' OR ProcessName LIKE '%WebMediaExtensions%') AND CommandLine CONTAINS suspicious_parameters🔗 References
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-28465
- https://www.zerodayinitiative.com/advisories/ZDI-21-572/
- https://www.zerodayinitiative.com/advisories/ZDI-21-579/
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-28465
- https://www.zerodayinitiative.com/advisories/ZDI-21-572/
- https://www.zerodayinitiative.com/advisories/ZDI-21-579/
