CVE-2016-5259 in Firefox
Summary
by MITRE
Use-after-free vulnerability in the CanonicalizeXPCOMParticipant function in Mozilla Firefox before 48.0 and Firefox ESR 45.x before 45.3 allows remote attackers to execute arbitrary code via a script that closes its own Service Worker within a nested sync event loop.
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Analysis
by VulDB Data Team • 09/09/2022
The CVE-2016-5259 vulnerability represents a critical use-after-free flaw in Mozilla Firefox's handling of XPCOM participants, specifically within the CanonicalizeXPCOMParticipant function. This vulnerability affects Firefox versions prior to 48.0 and Firefox ESR 45.x versions prior to 45.3, creating a significant security risk for users operating these outdated browser versions. The flaw stems from improper memory management during the execution of Service Worker operations, where the application fails to properly validate or manage object lifecycles when processing nested synchronous event loops.
The technical exploitation of this vulnerability occurs through a carefully crafted script that triggers a Service Worker to close itself while executing within a nested synchronous event loop context. This specific timing and execution pattern creates a scenario where freed memory locations are accessed after the original object has been deallocated, leading to undefined behavior and potential code execution. The vulnerability manifests when the browser's garbage collection process attempts to clean up resources while a nested event loop is still active, creating a race condition that can be exploited by malicious actors.
From an operational perspective, this vulnerability presents a severe risk to web application security and user privacy, as it allows remote attackers to execute arbitrary code on affected systems without requiring user interaction beyond visiting a malicious website. The use-after-free condition creates opportunities for attackers to manipulate memory contents, potentially leading to privilege escalation, information disclosure, or complete system compromise. The vulnerability's remote exploitability means that attackers can leverage this flaw from anywhere on the internet, making it particularly dangerous for widespread deployment.
The underlying cause of this vulnerability aligns with CWE-416, which describes the use of freed memory condition, and demonstrates how improper resource management in complex asynchronous programming environments can create exploitable conditions. Attackers can leverage this flaw through the attacker-controlled Service Worker API, which provides legitimate browser functionality that can be abused when combined with the memory management flaw. The vulnerability also intersects with ATT&CK technique T1059.007, which covers script-based execution through web browsers, as the exploit relies on JavaScript execution within the browser context to trigger the memory corruption.
Mitigation strategies for CVE-2016-5259 primarily focus on immediate browser updates to patched versions, which address the memory management issues in the CanonicalizeXPCOMParticipant function. Organizations should implement comprehensive patch management processes to ensure all Firefox installations are updated to versions 48.0 or later for regular Firefox releases, and 45.3 or later for ESR releases. Additionally, security teams should consider implementing network-based restrictions such as content filtering and web application firewalls to limit exposure while awaiting complete patch deployment. Browser security enhancements including sandboxing and strict memory access controls should be enabled to reduce the potential impact of any successful exploitation attempts. The vulnerability underscores the importance of regular security updates and proper memory management practices in modern web browsers.