CVE-2013-0756 in Firefox
Summary
by MITRE
Use-after-free vulnerability in the obj_toSource function in Mozilla Firefox before 18.0, Firefox ESR 17.x before 17.0.2, Thunderbird before 17.0.2, Thunderbird ESR 17.x before 17.0.2, and SeaMonkey before 2.15 allows remote attackers to execute arbitrary code via a crafted web page referencing JavaScript Proxy objects that are not properly handled during garbage collection.
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Analysis
by VulDB Data Team • 04/22/2021
The vulnerability identified as CVE-2013-0756 represents a critical use-after-free condition affecting Mozilla Firefox and related applications. This flaw exists within the obj_toSource function implementation and specifically targets the improper handling of JavaScript Proxy objects during garbage collection processes. The vulnerability affects multiple Mozilla products including Firefox versions prior to 18.0, Firefox ESR 17.x versions prior to 17.0.2, Thunderbird versions prior to 17.0.2, Thunderbird ESR 17.x versions prior to 17.0.2, and SeaMonkey versions prior to 2.15. The technical nature of this vulnerability places it firmly within the CWE-416 category of use-after-free conditions, which occurs when a program continues to reference memory after it has been freed, creating opportunities for malicious code execution.
The exploitation mechanism leverages JavaScript Proxy objects which are part of ECMAScript 6 specifications and provide a way to define custom behavior for fundamental operations. During the garbage collection process, when JavaScript Proxy objects are being cleaned up, the obj_toSource function fails to properly manage memory references, creating a scenario where freed memory can be accessed and potentially overwritten with malicious code. This particular implementation flaw allows attackers to craft specially designed web pages that trigger the problematic code path, enabling remote code execution capabilities. The vulnerability is particularly dangerous because it can be exploited through web-based attacks without requiring user interaction beyond visiting a malicious website, making it a prime target for drive-by download attacks and social engineering campaigns.
From an operational impact perspective, this vulnerability presents significant risks to organizations relying on affected Mozilla products, as it enables attackers to gain complete control over vulnerable systems. The use-after-free condition creates a memory corruption vulnerability that can be leveraged to execute arbitrary code with the privileges of the affected application, typically resulting in full system compromise. Attackers can exploit this vulnerability to install malware, steal sensitive data, or establish persistent access to target systems. The vulnerability's remote exploitability means that organizations cannot rely solely on network segmentation or firewall rules to protect against attacks, as the attack vector operates entirely through web browsers and standard HTTP protocols. This makes the vulnerability particularly concerning for enterprise environments where users frequently access untrusted web content.
Mitigation strategies for CVE-2013-0756 should prioritize immediate patch deployment across all affected Mozilla products, as the vulnerability has been fully documented and patched by Mozilla. Organizations should implement comprehensive browser security policies that include regular updates and patch management procedures to prevent exploitation of known vulnerabilities. Additional protective measures include implementing content security policies, using sandboxing technologies, and deploying web application firewalls to detect and block malicious content. Security teams should also consider implementing browser hardening configurations that disable unnecessary JavaScript features and restrict access to potentially dangerous APIs. The vulnerability demonstrates the importance of proper memory management in JavaScript engines and highlights the need for thorough testing of garbage collection processes when implementing new language features. Organizations should also monitor for related vulnerabilities in similar implementations and maintain awareness of the evolving threat landscape surrounding browser-based exploits and the ATT&CK framework's browser exploitation techniques.