CVE-2020-0640: Internet Explorer RCE Vulnerability

CVE-2020-0640 Overview

A remote code execution vulnerability exists when Internet Explorer improperly accesses objects in memory. This memory corruption vulnerability, classified as CWE-787 (Out-of-Bounds Write), allows attackers to execute arbitrary code in the context of the current user when a victim visits a specially crafted malicious webpage. Successful exploitation could grant attackers the same user rights as the current user, potentially leading to full system compromise if the user has administrative privileges.

Critical Impact

Remote attackers can execute arbitrary code on vulnerable systems by convincing users to visit malicious websites, potentially gaining complete control over affected Windows systems running Internet Explorer.

Affected Products

• Microsoft Internet Explorer 9, 10, and 11
• Microsoft Windows 7 SP1
• Microsoft Windows 8.1 and Windows RT 8.1
• Microsoft Windows 10 (all versions through 1909)
• Microsoft Windows Server 2008 SP2 and R2 SP1
• Microsoft Windows Server 2012 and R2
• Microsoft Windows Server 2016
• Microsoft Windows Server 2019

Discovery Timeline

• 2020-01-14 - CVE-2020-0640 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-0640

Vulnerability Analysis

This vulnerability stems from improper memory handling within Internet Explorer's rendering engine. When processing certain objects in memory, Internet Explorer fails to properly validate or handle memory access operations, resulting in an out-of-bounds write condition. This type of memory corruption can be leveraged by attackers to overwrite critical memory regions, manipulate program execution flow, and ultimately achieve arbitrary code execution.

The attack requires user interaction—specifically, the victim must navigate to a malicious webpage crafted by the attacker. The high attack complexity indicates that successful exploitation may require specific conditions or additional attack preparation. However, no privileges are required on the target system to initiate the attack, making this a significant threat for organizations with users browsing the internet using Internet Explorer.

Root Cause

The root cause of CVE-2020-0640 is an out-of-bounds write vulnerability (CWE-787) in Internet Explorer's memory access routines. When the browser processes specially crafted content, it fails to properly validate memory boundaries before writing data, allowing an attacker to corrupt adjacent memory locations. This improper memory access can lead to heap corruption, potentially allowing attackers to hijack execution flow and run malicious code.

Attack Vector

The attack vector for this vulnerability is network-based, requiring a victim to visit an attacker-controlled website or view malicious content embedded in a compromised legitimate site. Attackers could deliver the exploit through:

• Phishing emails containing links to malicious websites
• Compromised advertising networks (malvertising)
• Watering hole attacks targeting specific user groups
• Embedded malicious content in legitimate websites

The vulnerability affects Internet Explorer's core rendering functionality, meaning any method of loading malicious web content could potentially trigger the exploit. Once the victim visits the malicious page, the carefully crafted content triggers the memory corruption, allowing the attacker to execute code with the privileges of the logged-in user.

Detection Methods for CVE-2020-0640

Indicators of Compromise

• Unexpected Internet Explorer crashes or hangs when browsing specific websites
• Unusual child processes spawned by iexplore.exe
• Suspicious network connections originating from Internet Explorer processes
• Memory access violations or heap corruption events in Windows Event logs related to Internet Explorer

Detection Strategies

• Monitor for anomalous behavior from iexplore.exe processes, including unusual memory allocation patterns or process spawning
• Implement network-based intrusion detection to identify known exploit delivery mechanisms targeting browser vulnerabilities
• Deploy endpoint detection solutions capable of identifying memory corruption exploitation techniques
• Enable Windows Defender Exploit Guard or similar memory protection mechanisms to detect and block exploitation attempts

Monitoring Recommendations

• Configure application event logging to capture Internet Explorer crashes and exceptions
• Monitor process creation events for suspicious child processes of iexplore.exe
• Implement browser telemetry collection to identify visits to known malicious domains
• Review security logs for evidence of exploitation attempts, including DEP and ASLR bypass attempts

How to Mitigate CVE-2020-0640

Immediate Actions Required

• Apply Microsoft's January 2020 security updates immediately to all affected systems
• Consider migrating users from Internet Explorer to modern browsers such as Microsoft Edge, Chrome, or Firefox
• Restrict Internet Explorer usage through Group Policy if patching is not immediately possible
• Implement network segmentation to limit exposure of unpatched systems

Patch Information

Microsoft released security updates addressing CVE-2020-0640 as part of the January 2020 Patch Tuesday release. Organizations should apply the appropriate cumulative security update for their Windows version and Internet Explorer installation. For detailed patch information and download links, refer to the Microsoft Security Advisory for CVE-2020-0640.

Workarounds

• Disable Active Scripting in Internet Explorer through Internet Options security settings to reduce exploitation risk
• Configure Internet Explorer to prompt before running scripts by adjusting security zone settings
• Use Enhanced Protected Mode in Internet Explorer 11 where available to provide additional sandboxing
• Implement application whitelisting to prevent execution of unauthorized code even if exploitation succeeds
• Consider using Microsoft's Attack Surface Reduction rules to block exploitation techniques

# Disable Active Scripting via Registry (requires administrator privileges)
reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3" /v 1400 /t REG_DWORD /d 3 /f
# Value 3 = Disable, Value 1 = Enable, Value 0 = Prompt

# Enable Enhanced Protected Mode for Internet Explorer 11
reg add "HKCU\Software\Microsoft\Internet Explorer\Main" /v Isolation /t REG_SZ /d "PMEM" /f