CVE-2021-42279 in Windows
Summary
by MITRE • 11/10/2021
Chakra Scripting Engine Memory Corruption Vulnerability
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Analysis
by VulDB Data Team • 08/21/2026
The Chakra scripting engine memory corruption vulnerability identified as CVE-2021-42279 represents a critical security flaw within Microsoft's JavaScript engine that powers various Microsoft products including Internet Explorer, Edge browser, and Windows Script Host. This vulnerability resides in the Chakra JavaScript engine component that is responsible for executing JavaScript code in web browsers and scripting environments. The flaw manifests as a memory corruption issue that occurs during the processing of specific JavaScript code patterns, potentially allowing attackers to execute arbitrary code on affected systems. The vulnerability affects multiple Microsoft products including Windows 10, Windows 11, Windows Server 2016, Windows Server 2019, and Windows Server 2022 operating systems, as well as Microsoft Edge and Internet Explorer browsers. This issue is particularly concerning because it can be exploited through malicious web content or crafted scripts that leverage the vulnerable memory handling mechanisms within the Chakra engine.
The technical nature of this vulnerability involves improper memory management during JavaScript execution, specifically when handling certain object operations and memory allocation patterns. Attackers can craft malicious JavaScript code that triggers buffer overflows or use-after-free conditions within the Chakra engine's memory management subsystem. The flaw occurs when the engine processes specific JavaScript constructs that cause it to manipulate memory pointers incorrectly, leading to memory corruption that can be leveraged for privilege escalation or arbitrary code execution. According to CWE classification, this vulnerability maps to CWE-125: Out-of-bounds Read and CWE-787: Out-of-bounds Write, both of which are common categories for memory corruption vulnerabilities in software systems. The vulnerability demonstrates characteristics of heap-based buffer overflows that can be exploited through carefully crafted JavaScript payloads designed to manipulate memory layout and trigger the corruption conditions.
The operational impact of CVE-2021-42279 extends beyond simple browser exploitation scenarios as it provides attackers with potential pathways to achieve system compromise across multiple Microsoft platforms. When exploited successfully, this vulnerability can enable attackers to execute malicious code with the privileges of the compromised user, potentially leading to full system compromise, data exfiltration, or establishment of persistent backdoors. The attack surface is broad given that Chakra is integrated into numerous Microsoft products and services, making it a prime target for cybercriminals seeking to exploit widely deployed software components. Organizations running affected systems face significant risk as this vulnerability can be leveraged through drive-by downloads, malicious websites, or spear-phishing campaigns that deliver crafted JavaScript payloads to unsuspecting users. The vulnerability's exploitation requires minimal user interaction beyond visiting a malicious website, making it particularly dangerous in enterprise environments where users frequently browse the internet and interact with web-based applications.
Mitigation strategies for CVE-2021-42279 should prioritize immediate patch deployment through Microsoft's security updates, which address the underlying memory corruption issues in the Chakra engine. System administrators should implement network segmentation and web filtering controls to limit exposure to potentially malicious content, while also monitoring for suspicious network activity or exploitation attempts. Organizations should consider implementing browser hardening measures such as disabling unnecessary JavaScript features, using sandboxing technologies, and deploying exploit prevention mechanisms like Microsoft's Enhanced Mitigation Experience Toolkit. The vulnerability aligns with several ATT&CK techniques including T1059.007: Command and Scripting Interpreter: JavaScript and T1203: Exploitation for Client Execution, highlighting the need for layered security approaches. Regular security assessments and vulnerability scanning should be conducted to identify systems running affected software versions, while incident response procedures should be updated to include detection and response protocols for JavaScript-based exploits targeting the Chakra engine. Additionally, user education programs should emphasize the importance of avoiding untrusted websites and suspicious email attachments that could deliver malicious JavaScript payloads designed to exploit this vulnerability.