CVE-2012-3989 in Firefox
Summary
by MITRE
Mozilla Firefox before 16.0, Thunderbird before 16.0, and SeaMonkey before 2.13 do not properly perform a cast of an unspecified variable during use of the instanceof operator on a JavaScript object, which allows remote attackers to execute arbitrary code or cause a denial of service (assertion failure) via a crafted web site.
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Analysis
by VulDB Data Team • 04/18/2021
This vulnerability exists in Mozilla Firefox versions prior to 16.0, Thunderbird versions prior to 16.0, and SeaMonkey versions prior to 2.13 due to improper handling of type casting during instanceof operator evaluation. The flaw occurs when JavaScript objects are processed through the instanceof operator, where an unspecified variable undergoes incorrect casting operations that can lead to unpredictable behavior. This type of vulnerability falls under the category of improper type handling and memory corruption issues, typically classified as CWE-121 or CWE-122 depending on the specific manifestation. The vulnerability represents a classic buffer overflow or type confusion scenario that can be exploited through malicious web content.
The technical exploitation involves crafting a malicious website that triggers the problematic instanceof operator usage with specific JavaScript objects that cause the cast operation to fail. When the browser processes this malformed JavaScript code, the improper casting leads to an assertion failure that can be leveraged to execute arbitrary code on the target system. The assertion failure represents a fundamental breakdown in the JavaScript engine's type checking mechanisms, where the runtime environment fails to properly validate object types during instanceof evaluation. This vulnerability demonstrates a critical weakness in the JavaScript engine's memory management and type safety protocols, creating a pathway for remote code execution.
The operational impact of this vulnerability is severe as it enables remote attackers to execute arbitrary code on affected systems without user interaction. This makes it particularly dangerous for web-based attacks where users can be compromised simply by visiting a malicious website. The vulnerability affects not only web browsers but also email clients that use the same underlying JavaScript engine, expanding the attack surface significantly. Attackers can leverage this flaw to install malware, steal user data, or establish persistent backdoors on compromised systems. The denial of service aspect means that even successful exploitation without code execution can render the affected applications unusable, causing availability issues for users.
Mitigation strategies include immediate upgrade to patched versions of Firefox 16.0, Thunderbird 16.0, and SeaMonkey 2.13, which contain fixes for the type casting issue in the instanceof operator. Organizations should implement browser hardening measures such as disabling unnecessary JavaScript features, using content security policies, and deploying web application firewalls to filter malicious content. The vulnerability aligns with ATT&CK technique T1203 (Exploitation for Client Execution) and T1059 (Command and Scripting Interpreter) as it enables remote code execution through web-based attacks. Additionally, this vulnerability demonstrates the importance of proper input validation and type checking in interpreted languages, highlighting the need for robust defensive programming practices in JavaScript engines. Security monitoring should focus on detecting unusual JavaScript execution patterns and malformed instanceof operations that may indicate exploitation attempts.