Microsoft Internet Explorer jscript9.dll Memory Corruption Remote Code Execution Vulnerability (CVE-2020-1380)
Executive & SecOps Summary
SECOPS ASSESSMENTInternet Explorer 11 and Windows systems utilizing the jscript9.dll scripting engine
Attackers can execute arbitrary code with the privileges of the current user, potentially gaining full control of the affected system
Apply official Microsoft cumulative security updates immediately and transition to modern browsers
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Apply the latest cumulative security updates provided by Microsoft. You can force the installation of security updates using PowerShell.
# Install and import PSWindowsUpdate module to apply cumulative patches
Install-Module PSWindowsUpdate -Force -Verbose
Get-WindowsUpdate -AcceptAll -Install -AutoReboot2. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, restrict access to jscript.dll to prevent the scripting engine from executing.
:: Restrict access to jscript.dll for both 32-bit and 64-bit architectures
takeown /f %windir%\system32\jscript.dll
icacls %windir%\system32\jscript.dll /deny everyone:(F)
takeown /f %windir%\syswow64\jscript.dll
icacls %windir%\syswow64\jscript.dll /deny everyone:(F)3. Log Audit & IoC Verification Commands
Use the following PowerShell script to verify the file version of jscript9.dll on the system to determine patch status.
# Check the file version of jscript9.dll
$dllPath = '${env:windir}\system32\jscript9.dll'
if (Test-Path $dllPath) {
$fileVersion = (Get-Item $dllPath).VersionInfo.FileVersion
Write-Host 'Current jscript9.dll Version:' $fileVersion
} else {
Write-Host 'jscript9.dll is not present on this system.'
}Block Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
Protect unpatched Windows, Linux, and macOS workloads against in-memory exploitation and lateral movement with autonomous EDR.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2020-1380) is an Out-of-Bounds Write (CWE-787) memory corruption vulnerability in the jscript9.dll scripting engine of Microsoft Internet Explorer. The root cause lies in how the Just-In-Time (JIT) compiler optimizes specific array structures and object types, leading to Type Confusion. This allows an attacker to access freed memory or reference invalid pointers, enabling arbitrary memory writes.
2. Exploitation Mechanics & Attack Scenario
In a web-based attack scenario, an attacker hosts a specially crafted website designed to exploit this vulnerability through Internet Explorer and lures a user to visit it. Alternatively, the attacker can embed an ActiveX control marked 'safe for initialization' inside an application or Microsoft Office document that hosts the IE rendering engine. Once the victim opens the document or visits the site, the JIT compiler's flawed optimization routine is triggered, bypassing memory protections (DEP/ASLR) to execute shellcode under the context of the current user.
3. Infrastructure & Business Impact
This vulnerability is actively exploited in the wild and is listed in the CISA KEV catalog. If successfully exploited by an attacker targeting a user with administrative privileges, the attacker can take complete control of the system. This includes installing unauthorized programs, viewing, altering, or deleting sensitive data, and creating new accounts with full administrative rights to move laterally within the corporate network.
Official Vendor Advisories & References
A remote code execution vulnerability exists in the way that the scripting engine handles objects in memory in Internet Explorer. The vulnerability could corrupt memory in such a way that an attacker could execute arbitrary code in the context of the current user. An attacker who successfully exploited the vulnerability could gain the same user rights as the current user. If the current user is logged on with administrative user rights, an attacker who successfully exploited the vulnerability could take control of an affected system. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. In a web-based attack scenario, an attacker could host a specially crafted website that is designed to exploit the vulnerability through Internet Explorer and then convince a user to view the website. An attacker could also embed an ActiveX control marked "safe for initialization" in an application or Microsoft Office document that hosts the IE rendering engine. The attacker could also take advantage of compromised websites and websites that accept or host user-provided content or advertisements. These websites could contain specially crafted content that could exploit the vulnerability. The security update addresses the vulnerability by modifying how the scripting engine handles objects in memory.
Frequently Asked SecOps Questions (CVE-2020-1380)
FAQQ1. How critical is CVE-2020-1380 and is it actively exploited in the wild?
CVE-2020-1380 is rated CVSS 7.8 (HIGH) with a 30-day EPSS exploitation probability of 24.2%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2020-1380?
Primary impacted vendors include microsoft across internet explorer, windows. Scope summary: All Windows operating systems (including Windows 7, 8.1, 10, and Windows Server 2008/2012/2016/2019) running Internet Explorer 11
Q3. What temporary mitigations or workarounds exist for CVE-2020-1380 before patching?
[Mitigation] Apply official Microsoft cumulative security updates immediately and transition to modern browsers Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2020-1380
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