CVE-2018-5092 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur when the thread for a Web Worker is freed from memory prematurely instead of from memory in the main thread while cancelling fetch operations. This vulnerability affects Firefox < 58.
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Analysis
by VulDB Data Team • 12/30/2019
The vulnerability identified as CVE-2018-5092 represents a critical use-after-free condition that manifests in the Firefox browser's handling of Web Worker threads during fetch operation cancellation. This flaw occurs when the browser's memory management system prematurely releases memory associated with a Web Worker thread instead of properly managing the cleanup process within the main thread context. The improper memory deallocation creates a scenario where subsequent operations may attempt to access freed memory locations, leading to potential code execution or system instability. This vulnerability specifically impacts Firefox versions prior to 58, indicating that the issue was present in the browser's threading and memory management subsystems for an extended period. The flaw demonstrates a fundamental failure in the browser's concurrent processing model where the separation of concerns between main thread and worker thread memory management becomes compromised during asynchronous operation cancellation.
The technical implementation of this vulnerability stems from improper synchronization mechanisms within Firefox's Web Worker implementation. When fetch operations are cancelled, the browser's internal thread management system fails to properly coordinate between the main thread and worker thread memory cleanup processes. The use-after-free condition typically occurs because the memory allocation tracking system does not maintain proper reference counts or lifecycle management for thread resources during the cancellation sequence. This creates a window where a worker thread can be deallocated while still referenced by ongoing operations or pending callbacks, resulting in memory corruption that can be exploited by malicious actors. The vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software systems. The flaw represents a classic memory safety issue where the application's memory management logic fails to account for the temporal aspects of thread lifecycle management and resource cleanup.
The operational impact of CVE-2018-5092 extends beyond simple browser instability to potentially enable remote code execution capabilities. Attackers can leverage this vulnerability by crafting malicious web content that triggers fetch operations within Web Workers and subsequently cancels them in a manner that exploits the premature memory deallocation. The vulnerability is particularly concerning because it operates within the browser's core concurrency model, making it difficult to detect and prevent through traditional security measures. Successful exploitation could allow attackers to execute arbitrary code with the privileges of the browser process, potentially leading to complete system compromise. This aligns with ATT&CK technique T1059.007, which covers scripting languages and command execution through browser-based attack vectors. The vulnerability affects the browser's security model by creating an attack surface that bypasses typical sandboxing mechanisms, as the flaw exists within the legitimate browser functionality rather than external malicious code execution.
Mitigation strategies for CVE-2018-5092 primarily focus on immediate browser updates to versions 58 or later where the vulnerability has been patched. Organizations should implement comprehensive browser update policies to ensure all users operate on patched versions. Security researchers and system administrators should monitor for exploitation attempts through network traffic analysis and browser security logging. The patch for this vulnerability typically involves implementing proper memory management synchronization between main thread and worker thread cleanup processes, ensuring that thread resources are not prematurely deallocated during fetch operation cancellation. Additional protective measures include implementing Content Security Policy directives to limit Web Worker usage where possible, using browser security extensions, and maintaining regular security assessments of web applications that may be vulnerable to this class of attack. The vulnerability serves as a reminder of the critical importance of proper memory management in concurrent programming environments and the need for thorough testing of thread lifecycle management in complex software systems.