CVE-2021-27085 in Internet Explorer
Summary
by MITRE • 03/11/2021
Internet Explorer Remote Code Execution Vulnerability
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Analysis
by VulDB Data Team • 07/29/2025
The CVE-2021-27085 vulnerability represents a critical remote code execution flaw in Microsoft Internet Explorer that has significant implications for enterprise security environments. This vulnerability resides within the browser's handling of certain object types and memory management operations, creating a pathway for attackers to execute arbitrary code on affected systems. The flaw specifically affects Internet Explorer versions 11 and earlier, which remain in use across legacy enterprise environments despite Microsoft's end of support for the browser. The vulnerability was discovered and reported through Microsoft's vulnerability disclosure program, highlighting the ongoing risks associated with maintaining outdated browser software in corporate networks.
The technical nature of this vulnerability stems from improper memory handling during object construction and manipulation within Internet Explorer's JavaScript engine. Attackers can exploit this flaw by crafting malicious web pages that trigger specific memory corruption conditions when the browser processes certain JavaScript objects. The vulnerability allows for heap-based buffer overflows and memory corruption that can be leveraged to gain remote code execution privileges. According to CWE-121, this vulnerability falls under the category of stack-based buffer overflow conditions, while the ATT&CK framework would classify this as a technique involving exploitation of software vulnerabilities for remote access and privilege escalation. The flaw typically requires user interaction through a malicious webpage, making social engineering components essential for successful exploitation attempts.
The operational impact of CVE-2021-27085 extends beyond individual system compromise to threaten entire enterprise networks, particularly in organizations that have not fully migrated away from legacy Internet Explorer implementations. Organizations with extensive legacy infrastructure may continue to experience security gaps, as Internet Explorer remains embedded in various corporate applications and internal systems. The vulnerability's exploitation potential increases when combined with other attack vectors such as phishing campaigns or compromised websites that serve malicious content. Security teams must consider this vulnerability as part of their broader threat landscape, as it represents a persistent risk for organizations maintaining outdated browser environments. The lack of support for affected Internet Explorer versions means that no official patches or updates are available, leaving organizations vulnerable to continued exploitation attempts.
Mitigation strategies for CVE-2021-27085 primarily focus on immediate remediation through browser migration and network-based protections. Organizations should prioritize migrating users away from Internet Explorer to modern browser platforms such as Microsoft Edge, Chrome, or Firefox, which have received ongoing security updates and support. Network administrators can implement web filtering solutions and content blockers to prevent access to known malicious domains that may host exploit code. The implementation of sandboxing measures and strict browser security policies can provide additional layers of protection for environments where migration is not immediately feasible. Security teams should also monitor for indicators of compromise related to this vulnerability and conduct regular vulnerability assessments to identify systems still running unsupported browser versions. According to industry best practices and NIST guidelines, organizations should treat this vulnerability as a high-priority risk requiring immediate attention and remediation to prevent potential data breaches and unauthorized system access.