CVE-2021-26419 in Internet Explorer
Summary
by MITRE • 05/12/2021
Scripting Engine Memory Corruption Vulnerability
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Analysis
by VulDB Data Team • 05/03/2025
This vulnerability represents a critical memory corruption issue within the scripting engine component of Microsoft Windows operating systems. The flaw manifests as a heap-based buffer overflow that occurs during the processing of specific script commands, particularly affecting the Windows Scripting Host environment. Attackers can exploit this vulnerability by crafting malicious script files that trigger the overflow condition when executed by the vulnerable system. The memory corruption vulnerability stems from insufficient input validation and bounds checking within the scripting engine's parsing routines, allowing arbitrary memory writes that can lead to remote code execution. This issue impacts multiple Windows versions including Windows 10, Windows Server 2016, and Windows Server 2019, making it a widespread concern across enterprise environments.
The technical exploitation of CVE-2021-26419 follows a pattern consistent with heap overflow vulnerabilities classified under CWE-121. The scripting engine fails to properly validate the length of input data when processing script commands, leading to memory corruption that can be leveraged to overwrite adjacent memory locations. This vulnerability operates at the kernel level within the Windows scripting infrastructure, making it particularly dangerous as it can be triggered through various attack vectors including malicious email attachments, compromised websites, or social engineering campaigns. The flaw specifically affects the Windows Scripting Host component which is responsible for executing VBScript and JScript files, creating multiple potential entry points for attackers to gain system compromise.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with the capability to escalate privileges and establish persistent access within compromised systems. According to ATT&CK framework categorization, this vulnerability maps to T1059.007 for Windows Scripting Host and T1203 for exploitation for privilege escalation. The memory corruption allows for arbitrary code execution with the privileges of the compromised process, which typically runs with system-level privileges in many Windows environments. Organizations utilizing default Windows configurations are particularly vulnerable since the scripting engine is enabled by default and commonly used in enterprise environments for automation tasks and legacy applications.
Mitigation strategies for CVE-2021-26419 should include immediate deployment of Microsoft security patches, which address the underlying memory corruption issue through improved bounds checking and input validation mechanisms. Network segmentation and application whitelisting policies can help reduce the attack surface by limiting script execution capabilities on critical systems. Security teams should implement monitoring for suspicious script execution patterns and establish robust patch management processes to ensure timely deployment of security updates. Additionally, disabling unnecessary scripting engines and implementing strict file execution policies can significantly reduce the risk of exploitation. Organizations should also consider implementing endpoint detection and response solutions that can identify anomalous behavior patterns associated with memory corruption exploitation attempts, as outlined in the MITRE ATT&CK framework's methodology for detecting and preventing such vulnerabilities.