CVE-2020-6539 in Chrome
Summary
by MITRE
Use after free in CSS in Google Chrome prior to 84.0.4147.105 allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page.
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Analysis
by VulDB Data Team • 05/05/2025
The vulnerability identified as CVE-2020-6539 represents a critical use-after-free condition affecting the Cascading Style Sheets implementation within Google Chrome browser versions prior to 84.0.4147.105. This flaw resides in the browser's rendering engine where improper memory management allows attackers to manipulate heap memory structures through carefully crafted HTML content. The issue stems from the browser's failure to properly validate memory references after objects have been freed, creating opportunities for malicious code execution. According to CWE-416, this vulnerability specifically manifests as a use-after-free error where memory is accessed after it has been deallocated, violating fundamental memory safety principles that are essential for secure software operation.
The technical exploitation of this vulnerability occurs when a remote attacker crafts an HTML page containing malicious CSS elements that trigger the flawed memory management pathway. When Chrome processes such content, the CSS parser creates objects in memory that are subsequently freed, but the browser fails to properly invalidate references to these freed memory locations. Attackers can leverage this by controlling the heap layout and manipulating memory contents to execute arbitrary code with the privileges of the browser process. This type of vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter and T1203 for exploitation for execution, as it enables remote code execution through browser-based attack vectors.
The operational impact of CVE-2020-6539 extends beyond simple browser compromise, as successful exploitation can lead to complete system takeover when combined with other attack vectors. The heap corruption vulnerability allows attackers to potentially overwrite critical memory structures, inject malicious code, or escalate privileges within the compromised browser environment. This makes the vulnerability particularly dangerous in enterprise environments where browser-based attacks are commonly used as initial access points. The vulnerability affects not only individual users but also organizations that rely on Chrome for business operations, as it can be exploited through various attack surfaces including webmail, corporate portals, and social engineering campaigns. Organizations running affected Chrome versions face significant risk of data breaches, lateral movement within networks, and persistent threats that can remain undetected for extended periods.
Mitigation strategies for CVE-2020-6539 primarily involve immediate patching of Chrome browser installations to versions 84.0.4147.105 or later where the vulnerability has been addressed. Security administrators should implement comprehensive browser update policies and automated patch management systems to ensure timely deployment of security fixes. Additional protective measures include implementing content security policies to restrict external script execution, deploying web application firewalls to filter malicious content, and establishing user education programs to recognize suspicious web content. Network monitoring solutions should be configured to detect unusual outbound connections that may indicate successful exploitation attempts. The vulnerability demonstrates the critical importance of maintaining up-to-date software versions and implementing defense-in-depth strategies as outlined in NIST SP 800-53 security controls, particularly focusing on configuration management and vulnerability management practices. Organizations should also consider implementing sandboxing technologies and privilege separation mechanisms to limit the potential impact of successful exploitation attempts.