CVE-2020-17048: Microsoft Edge Buffer Overflow Vulnerability

CVE-2020-17048 Overview

CVE-2020-17048 is a memory corruption vulnerability in the Chakra Scripting Engine, the JavaScript engine used by Microsoft Edge (Legacy). This vulnerability allows remote attackers to execute arbitrary code on affected systems by exploiting improper memory handling within the scripting engine. When a user visits a maliciously crafted web page or processes specially crafted JavaScript content, the vulnerability can be triggered, potentially leading to complete system compromise.

Critical Impact

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code with the same privileges as the current user, potentially leading to full system compromise on affected Windows systems.

Affected Products

• Microsoft Edge (Legacy)
• Microsoft Windows 10 (versions 1607, 1803, 1809, 1903, 1909, 2004, 20H2)
• Microsoft Windows Server 2016
• Microsoft Windows Server 2019
• Microsoft ChakraCore

Discovery Timeline

• November 11, 2020 - CVE-2020-17048 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-17048

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write), indicating that the Chakra Scripting Engine fails to properly validate memory boundaries during certain JavaScript operations. The flaw exists in how the engine handles specific JavaScript constructs, allowing attackers to write data beyond allocated memory buffers.

The vulnerability requires an attacker to craft malicious JavaScript code that triggers the memory corruption condition. While exploitation requires winning a race condition or navigating specific memory layouts (reflected in the high attack complexity), no authentication or user interaction beyond visiting a malicious page is required.

Root Cause

The root cause of CVE-2020-17048 lies in improper bounds checking within the Chakra JavaScript engine. During the processing of certain JavaScript operations, the engine fails to adequately validate the boundaries of memory allocations, allowing an attacker to write data beyond the intended buffer boundaries. This out-of-bounds write condition can corrupt adjacent memory structures, potentially overwriting critical data such as function pointers or object metadata.

Attack Vector

The attack vector for this vulnerability is network-based, typically exploited through web-based delivery mechanisms. An attacker would need to convince a user to visit a malicious website or view content rendered by Microsoft Edge (Legacy) that contains specially crafted JavaScript. The malicious JavaScript would trigger the memory corruption vulnerability in the Chakra engine, potentially allowing code execution in the context of the current user.

The exploitation scenario typically involves:

1. Hosting malicious JavaScript on an attacker-controlled website
2. Luring victims to visit the malicious page through phishing or malvertising
3. The Chakra engine processes the malicious script and triggers the out-of-bounds write
4. Attacker-controlled data overwrites critical memory structures
5. Code execution occurs with the privileges of the current user

Detection Methods for CVE-2020-17048

Indicators of Compromise

• Unexpected crashes or restarts of Microsoft Edge (Legacy) browser processes
• Anomalous JavaScript execution patterns in browser telemetry logs
• Suspicious network connections originating from MicrosoftEdge.exe or chakra.dll processes
• Memory access violations in Chakra-related modules detected by endpoint protection

Detection Strategies

• Deploy endpoint detection and response (EDR) solutions to monitor for exploitation attempts targeting browser scripting engines
• Enable Windows Defender Exploit Guard and Application Guard for browser isolation
• Monitor for anomalous child processes spawned by Microsoft Edge or ChakraCore
• Implement network-based detection for known exploit delivery patterns

Monitoring Recommendations

• Enable enhanced logging for browser process activities and JavaScript execution
• Configure security information and event management (SIEM) rules to alert on Edge process anomalies
• Monitor for unsigned DLL loads or suspicious memory allocation patterns in browser processes
• Review Windows Event Logs for application crashes involving chakra.dll

How to Mitigate CVE-2020-17048

Immediate Actions Required

• Apply the Microsoft security update for CVE-2020-17048 from the November 2020 Patch Tuesday release
• Consider migrating to Microsoft Edge (Chromium-based) which uses a different JavaScript engine and is not affected
• Restrict access to untrusted websites through web filtering solutions
• Enable Windows Defender Application Guard for additional browser isolation

Patch Information

Microsoft has released security updates to address this vulnerability as part of the November 2020 security updates. Organizations should apply the appropriate patches for their Windows versions immediately. Detailed patch information and download links are available through the Microsoft Security Advisory for CVE-2020-17048.

For Windows systems, use Windows Update or Windows Server Update Services (WSUS) to deploy the patches. For standalone ChakraCore deployments, update to the patched version available through the official Microsoft ChakraCore repository.

Workarounds

• Migrate to Microsoft Edge (Chromium-based) which uses the V8 JavaScript engine instead of Chakra
• Implement network segmentation to limit exposure of vulnerable systems to untrusted content
• Use browser isolation technologies such as Windows Defender Application Guard
• Restrict browsing to trusted sites through proxy or firewall policies until patches can be applied

# Enable Windows Defender Application Guard via PowerShell
Enable-WindowsOptionalFeature -Online -FeatureName Windows-Defender-ApplicationGuard -NoRestart

# Verify Application Guard is enabled
Get-WindowsOptionalFeature -Online -FeatureName Windows-Defender-ApplicationGuard