CVE-2020-0878 Overview
A remote code execution vulnerability exists in the way that Microsoft browsers access objects in memory. This memory corruption vulnerability could allow an attacker to execute arbitrary code in the context of the current user by corrupting memory through a specially crafted website. If the current user is logged on with administrative user rights, the attacker could take complete control of an affected system, including the ability to install programs, view, change, or delete data, or create new accounts with full user rights.
This vulnerability affects multiple Microsoft browser technologies including Internet Explorer 9 and 11, Microsoft Edge (EdgeHTML), and the ChakraCore JavaScript engine. The attack requires user interaction—an attacker must convince a user to visit a malicious website through social engineering tactics such as phishing emails, instant messages, or malicious email attachments.
Critical Impact
This vulnerability is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, indicating confirmed active exploitation in the wild. Successful exploitation grants attackers the same privileges as the current user, potentially enabling full system compromise with administrative access.
Affected Products
- Microsoft Internet Explorer 9 and 11
- Microsoft Edge (EdgeHTML-based)
- Microsoft ChakraCore JavaScript Engine
- Microsoft Windows 7 SP1
- Microsoft Windows 8.1 and Windows RT 8.1
- Microsoft Windows 10 (versions 1507, 1607, 1709, 1803, 1809, 1903, 1909, 2004)
- Microsoft Windows Server 2008 SP2 and R2 SP1
- Microsoft Windows Server 2012 and R2
- Microsoft Windows Server 2016
- Microsoft Windows Server 2019
Discovery Timeline
- September 11, 2020 - CVE-2020-0878 published to NVD
- February 23, 2026 - Last updated in NVD database
Technical Details for CVE-2020-0878
Vulnerability Analysis
This vulnerability is classified as CWE-787 (Out-of-Bounds Write), a memory corruption flaw in Microsoft browser scripting engines. The vulnerability occurs when Microsoft browsers improperly handle objects in memory during JavaScript execution. When processing specially crafted web content, the browser's scripting engine fails to properly validate memory boundaries, allowing an attacker to write data outside the intended buffer boundaries.
The exploitation scenario requires an attacker to host malicious content on a website or compromise a legitimate website that accepts user-provided content. When a victim navigates to the malicious page, the crafted JavaScript triggers the out-of-bounds write condition, corrupting critical memory structures. This memory corruption can be leveraged to hijack program execution flow and execute attacker-controlled code.
The vulnerability's confirmed exploitation in the wild, as indicated by its CISA KEV listing, demonstrates that threat actors have developed reliable exploitation techniques for this flaw. The attack does not require authentication but does require user interaction to visit the malicious website.
Root Cause
The root cause of CVE-2020-0878 lies in improper memory handling within the Microsoft browser scripting engines. Specifically, when the JavaScript engine processes certain object operations, it fails to properly validate memory boundaries before writing data. This lack of bounds checking allows an attacker to craft JavaScript that triggers an out-of-bounds write operation, enabling memory corruption beyond the allocated buffer space. The affected components include the JScript engine in Internet Explorer and the Chakra JavaScript engine used in Microsoft Edge (EdgeHTML) and available as the standalone ChakraCore library.
Attack Vector
The attack vector for CVE-2020-0878 is network-based and requires user interaction. An attacker can exploit this vulnerability through several methods:
Malicious Website Hosting: The attacker hosts a specially crafted website containing JavaScript designed to trigger the memory corruption vulnerability. The attacker then uses social engineering tactics to convince users to visit the site.
Website Compromise: The attacker compromises legitimate websites or injects malicious content into websites that accept user-provided content or advertisements.
Phishing Campaigns: The attacker distributes links to the malicious content via phishing emails, instant messages, or by convincing users to open malicious email attachments that load web content.
When a vulnerable browser renders the attacker's crafted page, the malicious JavaScript executes and triggers the out-of-bounds write condition. The attacker can leverage this primitive to overwrite critical memory structures and ultimately achieve arbitrary code execution with the privileges of the browser process. If the user has administrative privileges, the attacker gains full control of the affected system.
Detection Methods for CVE-2020-0878
Indicators of Compromise
- Unexpected browser crashes or unusual browser behavior when visiting unfamiliar websites
- Detection of obfuscated JavaScript payloads in web traffic or browser cache
- Unusual process spawning from iexplore.exe, MicrosoftEdge.exe, or MicrosoftEdgeCP.exe processes
- Memory corruption artifacts or heap spray patterns in browser process memory dumps
Detection Strategies
- Deploy endpoint detection and response (EDR) solutions capable of monitoring browser process behavior and detecting exploitation attempts
- Implement network monitoring to identify traffic to known malicious domains associated with exploitation campaigns
- Enable browser-level telemetry and security features such as Windows Defender Application Guard
- Monitor for suspicious JavaScript execution patterns using browser developer tools or security extensions
- Review Windows Event Logs for application crashes in browser processes with memory corruption indicators
Monitoring Recommendations
- Enable Enhanced Security Configuration on Internet Explorer for server environments
- Configure web proxies to log and inspect JavaScript content for known exploitation patterns
- Implement security information and event management (SIEM) rules to alert on browser process anomalies
- Monitor CISA alerts and threat intelligence feeds for updated indicators related to CVE-2020-0878 exploitation
How to Mitigate CVE-2020-0878
Immediate Actions Required
- Apply Microsoft's September 2020 security updates immediately to all affected systems
- Prioritize patching systems where users have administrative privileges, as exploitation impact is highest on these systems
- Consider migrating from Internet Explorer and legacy Edge to Microsoft Edge (Chromium-based), which is not affected by this vulnerability
- Implement network segmentation to limit lateral movement potential if exploitation occurs
- Enable Windows Defender Exploit Guard and other exploit mitigation features on affected systems
Patch Information
Microsoft released security updates addressing this vulnerability as part of the September 2020 Patch Tuesday release. The patch modifies how Microsoft browsers handle objects in memory, properly implementing bounds checking to prevent the out-of-bounds write condition. Organizations should apply the appropriate cumulative update for their Windows version and ensure both the operating system and browser components are updated.
Detailed patch information is available in the Microsoft Security Advisory for CVE-2020-0878. Additional information about this vulnerability's active exploitation status is available in the CISA Known Exploited Vulnerabilities Catalog.
Workarounds
- Restrict access to websites known to host malicious content using web filtering solutions
- Run Internet Explorer in Enhanced Protected Mode to limit the impact of successful exploitation
- Configure users to operate with standard (non-administrative) privileges to limit the impact of successful exploitation
- Disable JavaScript execution in Internet Explorer for untrusted zones if feasible for your environment
- Consider using Windows Defender Application Guard to isolate browser sessions from the host operating system
# Verify Internet Explorer version and patch status
wmic product where "name like 'Internet Explorer%%'" get name,version
# Enable Enhanced Protected Mode in Internet Explorer via registry
reg add "HKCU\Software\Microsoft\Internet Explorer\Main" /v Isolation /t REG_SZ /d PMEM /f
# Check Windows Update installation status for September 2020 updates
wmic qfe list brief | findstr "2020-09"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
