CVE-2015-4516 in Firefox
Summary
by MITRE
Mozilla Firefox before 41.0 allows remote attackers to bypass certain ECMAScript 5 (aka ES5) API protection mechanisms and modify immutable properties, and consequently execute arbitrary JavaScript code with chrome privileges, via a crafted web page that does not use ES5 APIs.
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Analysis
by VulDB Data Team • 06/19/2022
The vulnerability identified as CVE-2015-4516 represents a critical security flaw in Mozilla Firefox versions prior to 41.0 that undermines the browser's JavaScript execution environment and privilege separation mechanisms. This issue specifically targets the ECMAScript 5 implementation within Firefox's JavaScript engine, exposing a fundamental weakness in the browser's ability to enforce security boundaries between user-mode JavaScript and privileged chrome code. The vulnerability stems from insufficient validation of immutable property modifications, allowing malicious actors to circumvent intended security protections that should prevent unauthorized access to privileged JavaScript APIs.
The technical flaw manifests through the improper handling of ECMAScript 5 immutable property mechanisms, which are designed to prevent modification of certain object properties that should remain read-only or unchangeable. In Firefox versions before 41.0, the JavaScript engine failed to properly enforce these protections when processing crafted web pages that deliberately avoided using standard ES5 APIs. This allows attackers to manipulate internal JavaScript objects and their properties in ways that should have been prevented by the ES5 specification, ultimately enabling privilege escalation from regular web content to chrome-level privileges. The vulnerability specifically affects the engine's handling of Object.defineProperty and related methods that should enforce immutability constraints.
The operational impact of this vulnerability is severe as it enables remote code execution with elevated privileges, allowing attackers to bypass the browser's security model entirely. When successfully exploited, the vulnerability permits malicious web pages to gain access to chrome privileges, which typically include access to browser internals, file system operations, and other sensitive functions that should be restricted to trusted browser components. This privilege escalation capability means that attackers can execute arbitrary JavaScript code with the same privileges as the browser itself, potentially leading to complete system compromise through techniques such as credential theft, data exfiltration, or installation of persistent malware. The vulnerability is particularly dangerous because it does not require user interaction beyond visiting a malicious website.
Mitigation strategies for CVE-2015-4516 primarily focus on immediate browser updates to version 41.0 or later where the vulnerability has been patched. Organizations should implement comprehensive patch management procedures to ensure all Firefox installations are updated promptly. Additional protective measures include deploying web application firewalls, implementing strict content security policies, and utilizing sandboxing technologies that limit the potential impact of exploitation. From a cybersecurity perspective, this vulnerability aligns with CWE-284, which addresses improper access control in software implementations, and relates to ATT&CK technique T1059.007 for JavaScript execution and T1068 for privilege escalation. Network administrators should monitor for exploitation attempts through anomaly detection systems that can identify unusual JavaScript behavior patterns and ensure that browser security settings are configured to enforce strict security boundaries between different privilege levels.