CVE-2021-21204 in Chrome
Summary
by MITRE • 04/26/2021
Use after free in Blink in Google Chrome on OS X prior to 90.0.4430.72 allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page.
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Analysis
by VulDB Data Team • 04/30/2021
The vulnerability identified as CVE-2021-21204 represents a critical use-after-free flaw within the Blink rendering engine of Google Chrome, specifically affecting macOS systems running versions prior to 90.0.4430.72. This issue falls under the broader category of memory safety vulnerabilities and demonstrates how improper memory management can lead to severe security consequences in web browsers. The flaw exists in the way Blink handles certain HTML elements and their associated memory allocations, creating conditions where freed memory regions can be accessed after they have been deallocated by the application's memory manager.
The technical implementation of this vulnerability involves a scenario where a maliciously crafted HTML page can trigger a race condition or improper memory deallocation sequence within the Blink engine's object lifecycle management. When processing specific web content, the rendering engine allocates memory for certain DOM objects and subsequently frees this memory when the objects are no longer needed. However, under specific conditions involving complex HTML structures or JavaScript interactions, the application may continue to reference these freed memory locations, leading to what is known as a use-after-free condition. This type of vulnerability is particularly dangerous because it can result in arbitrary code execution when an attacker can predictably control the contents of the freed memory region.
From an operational impact perspective, this vulnerability creates a significant risk for end users who may encounter malicious websites or be tricked into visiting compromised web pages. The remote exploitation capability means that attackers do not need physical access to the target system or any form of local privilege escalation to leverage this vulnerability. The heap corruption that results from this use-after-free condition can potentially allow attackers to execute arbitrary code with the privileges of the Chrome process, which typically runs with the same privileges as the user. This could lead to complete system compromise, data exfiltration, or the installation of additional malicious software. The vulnerability's presence in the rendering engine makes it particularly concerning as it can be triggered simply by visiting a malicious website, making it a prime target for drive-by attacks that exploit user trust in web browsing activities.
The remediation strategy for CVE-2021-21204 focuses primarily on updating to Google Chrome version 90.0.4430.72 or later, which contains the necessary patches to address the memory management flaw in Blink. Organizations should implement comprehensive patch management procedures to ensure timely deployment of security updates across all affected systems. Additionally, browser hardening measures such as enabling sandboxing features, restricting web content execution, and implementing content security policies can provide additional layers of protection. Security researchers and organizations should also consider monitoring for exploitation attempts through network traffic analysis and endpoint detection systems that can identify suspicious web requests or memory access patterns that may indicate exploitation attempts. This vulnerability aligns with CWE-416, which describes the use of freed memory condition, and represents a common attack vector that maps to several ATT&CK techniques including T1059 for command and scripting interpreter and T1078 for valid accounts, as successful exploitation could lead to persistent access and command execution within compromised systems.