CVE-2021-23962 in Firefox
Summary
by MITRE • 02/26/2021
Incorrect use of the '' method could have led to a user-after-poison and a potentially exploitable crash. This vulnerability affects Firefox < 85.
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Analysis
by VulDB Data Team • 08/11/2025
The vulnerability identified as CVE-2021-23962 represents a critical memory safety issue within the Firefox web browser that could potentially lead to arbitrary code execution. This flaw manifests through improper handling of memory operations during specific browser processes, creating conditions where attackers might exploit the vulnerability to execute malicious code on affected systems. The issue specifically impacts Firefox versions prior to 85, making it a significant concern for users running older browser versions.
The technical root cause of this vulnerability stems from improper memory management practices within Firefox's internal codebase, particularly in how the browser handles certain memory allocation and deallocation operations. This incorrect usage pattern creates a user-after-poison scenario where memory that has been freed or deallocated becomes accessible to malicious code, allowing attackers to manipulate memory contents and potentially overwrite critical program data. The flaw falls under the category of memory safety vulnerabilities that are commonly classified as CWE-416, representing use after free conditions where program memory is accessed after it has been freed.
The operational impact of this vulnerability extends beyond simple browser crashes, as it creates a potential exploitation vector for remote code execution attacks. When a user visits a malicious website or interacts with specially crafted content, the vulnerability could be triggered to execute arbitrary code with the privileges of the browser process. This represents a significant threat to user security as it allows attackers to bypass normal security boundaries and potentially gain full control over the affected system. The vulnerability aligns with ATT&CK technique T1059, which covers command and scripting interpreter usage, as exploitation could involve executing malicious code through browser-based attack vectors.
The memory safety issue creates a particularly dangerous environment for attackers to exploit because it combines multiple attack surfaces within the browser's memory management system. The user-after-poison condition allows for precise memory corruption that can be leveraged to overwrite function pointers, return addresses, or other critical program structures. This makes the vulnerability highly attractive to threat actors seeking to establish persistent access or escalate privileges on compromised systems. The flaw demonstrates how seemingly minor memory handling errors can create significant security risks when combined with modern exploitation techniques.
Organizations and individuals should prioritize immediate remediation of this vulnerability by upgrading to Firefox version 85 or later, which includes patches addressing the memory management issues. Security teams should also implement network monitoring to detect potential exploitation attempts and consider deploying additional security controls such as sandboxing and memory protection mechanisms. The vulnerability highlights the importance of regular security updates and proper memory management practices in browser development, as these issues can have far-reaching consequences for end-user security. Additionally, implementing security awareness training for users about the importance of keeping software updated can help reduce the risk of exploitation through this and similar vulnerabilities.