CVE-2020-6576 in Chrome
Summary
by MITRE
Use after free in offscreen canvas in Google Chrome prior to 85.0.4183.102 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 CVE-2020-6576 represents a critical use-after-free flaw in Google Chrome's offscreen canvas implementation that existed prior to version 85.0.4183.102. This issue falls under the CWE-416 category of Use After Free, which occurs when a program continues to use a pointer after the memory it points to has been freed, potentially leading to unpredictable behavior and exploitation opportunities. The vulnerability specifically affects the offscreen canvas functionality that allows web applications to perform drawing operations in a hidden canvas element without rendering it to the screen.
The technical exploitation of this vulnerability involves a remote attacker crafting a malicious HTML page that triggers improper memory management within Chrome's rendering engine. When the browser processes such a page, the offscreen canvas implementation fails to properly manage object lifecycles, leading to a situation where freed memory locations are accessed after being reallocated. This heap corruption scenario enables attackers to potentially execute arbitrary code on the victim's system with the privileges of the Chrome process. The flaw demonstrates a classic memory safety issue where the application does not adequately track object references or properly handle memory deallocation sequences.
The operational impact of CVE-2020-6576 extends beyond simple privilege escalation as it provides a potential pathway for full system compromise. Attackers can leverage this vulnerability to bypass modern security mitigations such as address space layout randomization and data execution prevention, especially when combined with other exploitation techniques. The remote nature of the attack means that victims need only visit a malicious webpage to be compromised, making this vulnerability particularly dangerous in phishing campaigns or compromised websites. This type of vulnerability aligns with ATT&CK technique T1059.001 for command and scripting interpreter, as successful exploitation could enable attackers to execute malicious code through the browser environment.
Mitigation strategies for this vulnerability primarily focus on immediate remediation through Chrome updates to version 85.0.4183.102 or later, which includes proper memory management fixes for the offscreen canvas implementation. Organizations should implement comprehensive patch management processes to ensure timely deployment of security updates across all browser installations. Additional protective measures include browser hardening configurations such as disabling unnecessary canvas features, implementing content security policies to restrict malicious content, and deploying web application firewalls that can detect and block suspicious HTML content patterns. The vulnerability also highlights the importance of regular security audits and code reviews focusing on memory management practices, particularly in complex browser rendering engines where multiple subsystems interact through shared memory spaces.