CVE-2021-21202 in Chrome
Summary
by MITRE • 04/26/2021
Use after free in extensions in Google Chrome prior to 90.0.4430.72 allowed an attacker who convinced a user to install a malicious extension to potentially perform a sandbox escape via a crafted Chrome Extension.
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Analysis
by VulDB Data Team • 04/30/2021
This vulnerability represents a critical use-after-free condition in the Chrome extension system that could enable attackers to bypass sandbox protections and achieve privilege escalation. The flaw existed in Google Chrome versions prior to 90.0.4430.72 and specifically affected how the browser handled memory management within its extension subsystem. When a malicious extension was installed and executed, the vulnerability allowed an attacker to manipulate memory pointers that had already been freed, creating opportunities for arbitrary code execution beyond the intended sandbox boundaries.
The technical implementation of this vulnerability stems from improper memory management practices within Chrome's extension handling code. When extensions are loaded, Chrome allocates memory for extension objects and their associated data structures. However, in certain scenarios involving extension updates or removal processes, the memory management system failed to properly track object references, leading to situations where freed memory could still be accessed and manipulated by malicious code. This use-after-free condition creates a memory corruption vulnerability that can be exploited to execute arbitrary code with the privileges of the Chrome process.
From an operational perspective, this vulnerability poses significant risks to users who may inadvertently install malicious extensions from untrusted sources or be tricked into installing compromised extensions through social engineering tactics. The attack vector requires user interaction to install the malicious extension, but once installed, the vulnerability could be leveraged to escape the Chrome sandbox and potentially access system resources, user data, or other browser processes. This represents a sophisticated attack that combines extension installation with memory corruption exploitation to achieve elevated privileges within the browser environment.
The vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software systems. It also maps to several ATT&CK techniques including T1176 for Browser Extensions and T1059 for Command and Scripting Interpreter usage. The sandbox escape capability places this vulnerability in the category of advanced persistent threat vectors that could enable attackers to maintain long-term access to compromised systems. Organizations should prioritize immediate patching of affected Chrome versions to prevent exploitation, while also implementing extension management policies that restrict installation of unsigned or untrusted extensions. Additionally, monitoring for suspicious extension installations and behavioral anomalies in browser processes can help detect potential exploitation attempts. The incident highlights the importance of robust memory management practices in browser security architectures and demonstrates how seemingly isolated vulnerabilities in extension handling can have far-reaching implications for overall system security.