CVE-2021-4098 in Chrome
Summary
by MITRE • 02/12/2022
Insufficient data validation in Mojo in Google Chrome prior to 96.0.4664.110 allowed a remote attacker who had compromised the renderer process to potentially perform a sandbox escape via a crafted HTML page.
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Analysis
by VulDB Data Team • 02/16/2022
The vulnerability identified as CVE-2021-4098 represents a critical security flaw in Google Chrome's Mojo framework, which is a component designed to facilitate communication between different processes within the browser. This issue affects Chrome versions prior to 96.0.4664.110 and specifically targets the insufficient validation of data within the Mojo system. The vulnerability operates under the premise that an attacker who has already compromised the renderer process can exploit this weakness to escape the sandbox environment that normally protects the browser from malicious code execution. The Mojo framework serves as a core communication mechanism between Chrome's various processes including the renderer, browser, and utility processes, making it a prime target for attackers seeking to elevate their privileges within the browser sandbox.
The technical nature of this vulnerability stems from inadequate input validation within the Mojo message passing system, which allows malicious data to bypass security checks during inter-process communication. When a crafted HTML page is rendered, it can potentially manipulate the Mojo framework to execute code outside of the intended sandbox boundaries. This flaw falls under the CWE-20 category of "Improper Input Validation" and specifically relates to CWE-787 "Out-of-bounds Write" and CWE-252 "Unchecked Return Value" as the system fails to properly validate data integrity before processing. The vulnerability is particularly dangerous because it leverages a compromised renderer process, meaning the attacker has already gained some level of access to the browser environment. This makes the attack vector more realistic and potentially devastating, as it represents a privilege escalation attack that could allow an attacker to gain access to system resources that should be protected by the browser's security model.
The operational impact of CVE-2021-4098 extends beyond simple browser compromise, as successful exploitation could lead to complete system takeover by allowing attackers to escape the sandbox protection that is fundamental to modern browser security architectures. The attack scenario typically begins with a user visiting a malicious website that compromises the renderer process through techniques such as cross-site scripting or other initial exploitation methods. Once the renderer is compromised, the attacker can craft a specific HTML page that exploits the Mojo validation flaw to execute arbitrary code with elevated privileges. This could potentially lead to full system compromise, as the sandbox escape would allow access to the user's files, network communications, and other system resources that should normally be protected from browser-based attacks. The vulnerability directly relates to ATT&CK technique T1059.007 "Command and Scripting Interpreter: JavaScript' and T1068 'Exploitation for Privilege Escalation' within the MITRE ATT&CK framework.
Mitigation strategies for CVE-2021-4098 focus primarily on updating Chrome to version 96.0.4664.110 or later, which contains the necessary patches to address the insufficient data validation in the Mojo framework. Organizations should implement immediate patch management procedures to ensure all Chrome installations are updated, as this vulnerability is actively exploited in the wild. Additional protective measures include implementing strict content security policies, disabling unnecessary browser features, and using sandboxing solutions that provide additional layers of protection. Network monitoring should be enhanced to detect potential exploitation attempts through unusual Mojo communication patterns or unexpected privilege escalation behaviors. The fix implemented by Google addresses the root cause by strengthening the input validation mechanisms within the Mojo framework, ensuring that all data passed between processes is properly validated before being processed. Security teams should also consider implementing browser hardening measures such as disabling the use of potentially vulnerable JavaScript APIs and restricting access to system resources through additional security policies. Regular security assessments should be conducted to verify that the updated Chrome versions are properly configured and that no other vulnerabilities exist in the browser's communication frameworks that could be exploited in similar manners.