CVE-2021-21206 in Chrome
Summary
by MITRE • 04/26/2021
Use after free in Blink in Google Chrome prior to 89.0.4389.128 allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page.
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Analysis
by VulDB Data Team • 05/03/2025
The vulnerability CVE-2021-21206 represents a critical use-after-free flaw within the Blink rendering engine of Google Chrome, affecting versions prior to 89.0.4389.128. This issue stems from improper memory management during the handling of HTML elements, creating a scenario where freed memory locations could be accessed after their intended use. The vulnerability manifests when the browser processes specially crafted HTML content that triggers specific conditions within the Blink engine's memory allocation and deallocation mechanisms. Such flaws are particularly dangerous because they can lead to arbitrary code execution when an attacker successfully manipulates the memory state to redirect program flow.
The technical root cause of this vulnerability aligns with CWE-416, which describes the use of freed memory condition where a pointer is used after the memory it references has been freed. In the context of web browsers, this typically occurs when JavaScript or HTML elements reference DOM nodes that have been removed from memory but are still being accessed. The Blink engine's object lifecycle management fails to properly track references to freed objects, allowing an attacker to corrupt heap memory structures. This heap corruption can occur when multiple objects reference the same memory location, and one object is freed while another continues to reference it, creating a race condition or memory inconsistency that can be exploited.
From an operational perspective, this vulnerability enables remote code execution through a crafted HTML page, making it particularly dangerous in web environments where users may encounter malicious content. The attack vector requires no user interaction beyond visiting a malicious website, as the exploit can be triggered automatically when the browser renders the malicious HTML content. The impact extends beyond simple privilege escalation, as successful exploitation can allow attackers to execute arbitrary code with the privileges of the browser process, potentially leading to full system compromise. This vulnerability affects the core rendering functionality of Chrome, making it a high-value target for attackers seeking to compromise user systems.
The exploitation of this vulnerability typically follows the standard attack pattern of heap spraying or memory corruption techniques, where attackers craft HTML content that forces specific memory layouts to achieve code execution. The ATT&CK framework categorizes this as a technique involving memory corruption vulnerabilities, specifically targeting the browser's rendering engine through web-based attack vectors. Mitigation strategies include updating to Chrome version 89.0.4389.128 or later, which implements proper memory management fixes, and employing additional browser hardening measures such as sandboxing, content security policies, and regular security updates. Organizations should also consider implementing web application firewalls and monitoring for suspicious HTML content that might trigger similar memory corruption patterns. The vulnerability demonstrates the critical importance of proper memory management in complex software systems and highlights the need for continuous security auditing of core components like rendering engines.