CVE-2021-26419
📋 TL;DR
CVE-2021-26419 is a memory corruption vulnerability in Internet Explorer's scripting engine (jscript9.dll) that allows remote code execution. Attackers can exploit this by tricking users into visiting malicious websites, potentially taking control of affected systems. This primarily impacts users running vulnerable versions of Internet Explorer on Windows systems.
💻 Affected Systems
- Internet Explorer
- Microsoft Edge (IE mode)
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with attacker gaining full control, data theft, ransomware deployment, and lateral movement across networks.
Likely Case
Malware installation, credential theft, and system compromise when users visit malicious websites with Internet Explorer.
If Mitigated
Limited impact with proper patching, browser restrictions, and security controls preventing exploitation.
🎯 Exploit Status
Proof-of-concept code is publicly available, making exploitation feasible for attackers with moderate skills.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: March 2021 security updates or later
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26419
Restart Required: Yes
Instructions:
1. Apply March 2021 Windows security updates. 2. For Windows 10: Install KB5000802. 3. For Windows 8.1/Server 2012 R2: Install KB5000803. 4. Restart system after installation.
🔧 Temporary Workarounds
Disable Internet Explorer
windowsDisable Internet Explorer browser to prevent exploitation via malicious websites.
Disable-WindowsOptionalFeature -Online -FeatureName Internet-Explorer-Optional-amd64
Restrict Internet Explorer via Group Policy
windowsConfigure Group Policy to restrict Internet Explorer usage and prevent access to untrusted sites.
🧯 If You Can't Patch
- Disable Internet Explorer completely and use alternative browsers
- Implement application whitelisting to prevent execution of unauthorized code
🔍 How to Verify
Check if Vulnerable:
Check if Internet Explorer is installed and if March 2021 security updates are not applied.Check Version:
wmic qfe list | findstr KB5000802Verify Fix Applied:
Verify that March 2021 security updates (KB5000802 for Win10, KB5000803 for Win8.1/2012 R2) are installed.📡 Detection & Monitoring
Log Indicators:
- Internet Explorer crash logs, unexpected process creation from iexplore.exe
Network Indicators:
- Unusual outbound connections from systems using Internet Explorer
SIEM Query:
Process Creation where Image contains 'iexplore.exe' AND ParentImage contains 'explorer.exe' AND CommandLine contains suspicious patterns🔗 References
- http://packetstormsecurity.com/files/162570/Internet-Explorer-jscript9.dll-Memory-Corruption.html
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26419
- http://packetstormsecurity.com/files/162570/Internet-Explorer-jscript9.dll-Memory-Corruption.html
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26419
