CVE-2026-117872 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the JavaScript: Standard Library component. This vulnerability was fixed in Firefox 159, Firefox ESR 115.44, and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability represents a critical memory management error within the JavaScript engine of Mozilla Firefox, specifically categorized as an use-after-free condition in the Standard Library component. This type of flaw occurs when program execution attempts to access or manipulate a block of memory that has already been deallocated by the system. In the context of web browsers and their embedded scripting engines, such errors are particularly dangerous because they can be triggered through maliciously crafted JavaScript code hosted on untrusted websites. The vulnerability stems from improper handling of object lifecycles within the SpiderMonkey engine, where references to objects persist after those objects have been freed, leading to undefined behavior when subsequent operations attempt to read or write to that stale memory address.
From a technical perspective, use-after-free vulnerabilities are classified under CWE-416 in the Common Weakness Enumeration standard. This classification highlights the fundamental issue of referencing memory after it has been released, which violates safe programming practices and introduces instability into the application runtime. The specific manifestation within Firefox involves the JavaScript Standard Library, where internal data structures may retain pointers to objects that have been garbage collected or explicitly destroyed by script logic. When the browser processes a webpage containing exploit code designed to trigger this race condition or logical error, it can lead to arbitrary memory read and write capabilities for an attacker who successfully triggers the flaw.
The operational impact of this vulnerability is severe, as it allows remote attackers to execute arbitrary code on the victim's system with the privileges of the browser process. By leveraging a use-after-free bug, an attacker can potentially overwrite function pointers or object vtables in memory, thereby redirecting program execution flow to malicious shellcode injected into the heap or stack. This capability effectively bypasses many modern security mitigations such as Data Execution Prevention and Address Space Layout Randomization if exploited with sufficient precision. Consequently, a user visiting a specially crafted website could have their system fully compromised without any further interaction, leading to data theft, installation of malware, or use of the machine in botnets.
This vulnerability aligns closely with MITRE ATT&CK technique T1203, which covers Exploitation for Client Execution. The attack vector relies on social engineering elements where a user is lured into visiting a malicious site that hosts the exploit payload. Once executed, the browser process becomes the entry point for deeper system compromise. The severity of this issue necessitates immediate attention from security teams and end-users alike, as it represents a direct path to remote code execution through standard web browsing activities.
Mitigation strategies primarily involve ensuring that all instances of Firefox are updated to versions where this flaw has been patched. Specifically, users must upgrade to Firefox version 159 or later, which includes the necessary fixes for memory management in the JavaScript engine. For organizations relying on long-term support releases, it is critical to update to Firefox ESR 115.44 or Firefox ESR 153.6. These updates contain code changes that enforce stricter checks on object lifetimes and prevent access to freed memory regions. Additionally, deploying browser isolation technologies or sandboxing solutions can reduce the blast radius if a vulnerability is exploited by limiting the permissions granted to the browser process within the operating system environment.