CVE-2016-5255 in Firefox
Summary
by MITRE
Use-after-free vulnerability in the js::PreliminaryObjectArray::sweep function in Mozilla Firefox before 48.0 allows remote attackers to execute arbitrary code via crafted JavaScript that is mishandled during incremental garbage collection.
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Analysis
by VulDB Data Team • 03/16/2019
The vulnerability identified as CVE-2016-5255 represents a critical use-after-free condition within Mozilla Firefox's JavaScript engine, specifically within the js::PreliminaryObjectArray::sweep function. This flaw exists in versions prior to Firefox 48.0 and enables remote code execution through carefully crafted JavaScript payloads. The issue stems from improper memory management during incremental garbage collection processes, where objects are freed from memory but references to them persist, creating opportunities for malicious code to exploit the dangling pointers.
The technical implementation of this vulnerability occurs during the incremental garbage collection cycle when the js::PreliminaryObjectArray::sweep function processes objects that are scheduled for deletion. When the garbage collector encounters certain JavaScript constructs that trigger premature object cleanup, it fails to properly invalidate references to objects that have already been freed from memory. This creates a scenario where subsequent JavaScript operations can access memory locations that have been deallocated, allowing attackers to manipulate the memory layout and potentially execute arbitrary code. The vulnerability is particularly dangerous because it operates within the JavaScript engine's core memory management system, making it difficult to detect and prevent through standard security measures.
The operational impact of CVE-2016-5255 extends beyond simple remote code execution to encompass potential privilege escalation and system compromise. Attackers can leverage this vulnerability to bypass security restrictions and gain unauthorized access to system resources, making it a significant concern for enterprise environments where Firefox is widely deployed. The vulnerability's exploitation requires a crafted JavaScript payload that can trigger the specific memory management path, but once successful, it provides attackers with extensive control over the affected system. This type of vulnerability aligns with CWE-416, which describes use-after-free conditions, and represents a classic example of memory safety issues that have historically plagued web browsers due to their complex JavaScript execution environments.
Mitigation strategies for CVE-2016-5255 primarily focus on immediate version upgrades to Firefox 48.0 or later, which contain the necessary patches to address the memory management flaw. Organizations should implement comprehensive patch management procedures to ensure all Firefox installations are updated promptly, as this vulnerability has been actively exploited in the wild. Additional protective measures include implementing content security policies, enabling sandboxing features, and utilizing web application firewalls to detect and block malicious JavaScript payloads. The vulnerability demonstrates the importance of robust memory management practices in browser engines and highlights the need for continuous security auditing of core components. From an ATT&CK framework perspective, this vulnerability maps to techniques involving code injection and privilege escalation, with the exploitation process following the T1059.007 sub-technique for JavaScript-based attacks and potentially leading to T1068 for local privilege escalation. Organizations should also consider implementing browser hardening measures and monitoring for unusual JavaScript behavior that might indicate exploitation attempts.