CVE-2020-1380: Microsoft Internet Explorer RCE Vulnerability

CVE-2020-1380 Overview

CVE-2020-1380 is a critical remote code execution vulnerability affecting Microsoft Internet Explorer's scripting engine (jscript9.dll). The vulnerability exists in the way that the scripting engine handles objects in memory, allowing attackers to corrupt memory and execute arbitrary code in the context of the current user. This vulnerability has been confirmed as actively exploited in the wild and is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog.

Critical Impact

Successful exploitation allows attackers to execute arbitrary code with the same privileges as the current user. If the user has administrative rights, an attacker could take complete control of the affected system, install programs, view/change/delete data, or create new accounts with full user rights.

Affected Products

• Microsoft Internet Explorer 11
• Microsoft Windows 10 (versions 1507, 1607, 1709, 1803, 1809, 1903, 1909, 2004)
• Microsoft Windows 7 SP1
• Microsoft Windows 8.1
• Microsoft Windows RT 8.1
• Microsoft Windows Server 2008 R2 SP1
• Microsoft Windows Server 2012 / 2012 R2
• Microsoft Windows Server 2016
• Microsoft Windows Server 2019

Discovery Timeline

• 2020-08-17 - CVE-2020-1380 published to NVD
• 2026-02-23 - Last updated in NVD database

Technical Details for CVE-2020-1380

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write), a memory corruption flaw in Internet Explorer's JavaScript engine (jscript9.dll). The scripting engine fails to properly handle objects in memory during JavaScript execution, leading to memory corruption that can be exploited for arbitrary code execution.

The attack surface is particularly concerning because Internet Explorer's rendering engine can be invoked through multiple vectors beyond the browser itself. ActiveX controls marked as "safe for initialization" can be embedded in Microsoft Office documents or other applications that host the IE rendering engine, significantly expanding the potential attack paths.

Root Cause

The root cause lies in improper memory handling within the JScript9 scripting engine. When processing certain JavaScript objects, the engine fails to properly validate or manage memory operations, resulting in an out-of-bounds write condition. This memory corruption can be leveraged by attackers to overwrite critical memory structures and gain control of program execution flow.

Attack Vector

Exploitation requires user interaction, typically convincing a victim to visit a malicious website or open a specially crafted document. Attack scenarios include:

Web-Based Attack: An attacker hosts a specially crafted website designed to exploit the vulnerability through Internet Explorer and convinces the user to visit the site through phishing or social engineering techniques.

Document-Based Attack: An attacker embeds a malicious ActiveX control in a Microsoft Office document that invokes the IE rendering engine when opened.

Compromised Website Attack: Attackers inject malicious content into compromised websites or websites that accept user-provided content or advertisements.

The network-based attack vector with low complexity and no privilege requirements makes this vulnerability particularly dangerous, especially given its confirmed exploitation in targeted attacks.

Detection Methods for CVE-2020-1380

Indicators of Compromise

• Suspicious JavaScript execution patterns in Internet Explorer or IE-based rendering contexts
• Anomalous memory access patterns or crashes in jscript9.dll
• Unexpected process spawning from iexplore.exe or Office applications hosting IE rendering engine
• Network connections to known malicious domains following document or webpage access

Detection Strategies

• Monitor for exploitation attempts using endpoint detection and response (EDR) solutions that track JavaScript engine behavior
• Implement network-based intrusion detection rules for known exploitation patterns targeting CVE-2020-1380
• Deploy behavioral analysis to detect memory corruption attacks in browser processes
• Review Windows Event Logs for application crashes related to Internet Explorer or jscript9.dll

Monitoring Recommendations

• Enable detailed logging for Internet Explorer and related processes
• Configure security information and event management (SIEM) systems to alert on Internet Explorer exploitation indicators
• Monitor for unusual child process creation from browser or Office application processes
• Track network traffic for connections to domains associated with exploitation campaigns

How to Mitigate CVE-2020-1380

Immediate Actions Required

• Apply the Microsoft security update for CVE-2020-1380 immediately as this vulnerability is actively exploited
• Restrict Internet Explorer usage and migrate to modern browsers where possible
• Disable JScript execution through Group Policy if not required for business operations
• Implement application whitelisting to prevent execution of malicious payloads
• Ensure users operate with least-privilege accounts to limit exploitation impact

Patch Information

Microsoft has released security updates to address this vulnerability. The patch modifies how the scripting engine handles objects in memory, correcting the out-of-bounds write condition. Organizations should apply the security update available through the Microsoft Security Advisory and Windows Update.

For systems that cannot be immediately patched, administrators should consider restricting access to jscript9.dll or implementing additional compensating controls.

Workarounds

• Restrict ActiveX controls in Office documents by configuring Protected View settings
• Disable the JScript scripting engine in Internet Explorer through registry modifications or Group Policy
• Block external content in Office applications to prevent exploitation via embedded ActiveX controls
• Implement network segmentation to limit the impact of potential compromises

# Restrict JScript execution via Registry (run as Administrator)
# WARNING: This may affect legitimate functionality - test before deployment
reg add "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_RESTRICT_LEGACY_JSCRIPT_PER_SECURITY_ZONE" /v "iexplore.exe" /t REG_DWORD /d 1 /f