CVE-2015-4484 in Firefox
Summary
by MITRE
The js::jit::AssemblerX86Shared::lock_addl function in the JavaScript implementation in Mozilla Firefox before 40.0 and Firefox ESR 38.x before 38.2 allows remote attackers to cause a denial of service (application crash) by leveraging the use of shared memory and accessing (1) an Atomics object or (2) a SharedArrayBuffer object.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 10/22/2024
The vulnerability identified as CVE-2015-4484 represents a critical denial of service flaw within the JavaScript engine of Mozilla Firefox versions prior to 40.0 and Firefox ESR 38.x versions prior to 38.2. This issue resides in the js::jit::AssemblerX86Shared::lock_addl function which is part of the Just-In-Time compilation infrastructure that optimizes JavaScript execution on x86 architectures. The flaw specifically manifests when the JavaScript engine processes shared memory operations involving Atomics objects or SharedArrayBuffer objects, creating a scenario where remote attackers can exploit this weakness to crash the application.
The technical root cause of this vulnerability stems from improper handling of memory synchronization operations within the JIT compiler's assembly code generation. When the lock_addl function attempts to generate atomic addition instructions for shared memory regions, it fails to properly validate or handle certain edge cases involving shared memory objects. This function is designed to create lock-free atomic operations using the x86 lock prefix, but the implementation contains a flaw that allows for invalid memory access patterns when dealing with shared memory structures. The vulnerability specifically occurs during the compilation phase of JavaScript code that utilizes the Atomics API or SharedArrayBuffer objects, which are part of the web platform's concurrent programming capabilities.
The operational impact of this vulnerability extends beyond simple application instability, as it provides remote attackers with a reliable method to cause denial of service attacks against Firefox users. Attackers can craft malicious JavaScript code that specifically targets shared memory operations, causing the browser to crash when attempting to compile such code through the JIT compiler. This creates a significant risk for web applications that may inadvertently expose users to malicious content or for attackers who can inject JavaScript into web pages. The vulnerability affects the browser's ability to maintain stable execution of JavaScript code, potentially leading to complete application crashes and requiring users to restart their browsers. The flaw is particularly concerning because it operates at the core JIT compilation layer, meaning it can affect a wide range of legitimate JavaScript operations that happen to involve shared memory constructs.
This vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and relates to the broader category of memory safety issues in concurrent programming environments. From an ATT&CK framework perspective, this represents a privilege escalation technique through application crash exploitation, potentially falling under the T1499.004 sub-technique for network denial of service. The flaw demonstrates poor input validation in the JIT compiler's code generation process, particularly when handling shared memory objects that are part of the modern web platform's threading capabilities. The vulnerability's exploitation requires no special privileges beyond the ability to execute JavaScript in a browser context, making it particularly dangerous for web-based attack scenarios. Security practitioners should note that this vulnerability highlights the complexity of implementing safe concurrent programming features in web browsers, particularly when combining JIT compilation with shared memory operations.
The recommended mitigations for this vulnerability include immediate upgrade to Firefox version 40.0 or Firefox ESR 38.2, which contain the necessary patches to address the improper memory handling in the JIT compiler. Organizations should also implement browser hardening measures such as disabling unnecessary JavaScript features, implementing content security policies, and monitoring for suspicious JavaScript behavior patterns. Additionally, web developers should be cautious when implementing shared memory operations in their applications and ensure proper validation of shared memory objects. The patch for this vulnerability specifically addresses the memory access patterns in the lock_addl function and includes proper bounds checking for shared memory operations. Security teams should monitor for any related vulnerabilities in the JIT compilation subsystem and consider implementing sandboxing measures to limit the impact of potential exploitation attempts.