CVE-2026-109716 in Firefox
Summary
by MITRE • 10/13/2026
Incorrect boundary conditions in the JavaScript Engine component. This vulnerability was fixed in Firefox 158, Firefox ESR 115.43, and Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/13/2026
The identified security issue resides within the core JavaScript engine implementation of Mozilla Firefox, specifically concerning incorrect boundary conditions during memory access operations. This type of vulnerability typically arises when the runtime environment fails to properly validate array indices or buffer offsets before performing read or write actions on allocated memory regions. In complex scripting environments like SpiderMonkey, which powers Firefox's JavaScript execution, such errors can lead to out-of-bounds reads or writes if the engine does not correctly enforce limits defined by the source code logic against actual data sizes. The flaw suggests a lapse in static analysis or runtime checks that are designed to prevent access beyond the allocated memory boundaries, allowing potentially malicious scripts to interact with memory locations outside their intended scope.
From a technical perspective, this vulnerability falls under the category of improper input validation and boundary condition errors, which aligns closely with Common Weakness Enumeration identifier CWE-125 for out-of-bounds read or CWE-787 for out-of-bounds write depending on the specific nature of the memory access violation. Such flaws are particularly dangerous because they can be exploited to achieve arbitrary code execution if an attacker can control the data being written or read through crafted JavaScript payloads. The exploitation vector often involves triggering a heap overflow or underflow, which may allow an adversary to corrupt adjacent memory structures, overwrite function pointers, or leak sensitive information from other parts of the browser process. This aligns with ATT&CK techniques related to execution via script interpreters and potential privilege escalation within the sandboxed environment if additional exploitation chains are present.
The operational impact of this vulnerability is significant for users relying on Firefox for browsing untrusted web content. An attacker hosting a malicious website could potentially craft specific JavaScript code that triggers these boundary condition errors when processed by the browser engine. Successful exploitation could lead to remote code execution, allowing the compromise of the user's system under the context of the current user account. This undermines the security model of the browser, which relies on strict isolation between web content and local resources. The risk is heightened in scenarios where users visit compromised or maliciously designed sites that attempt to exploit known weaknesses in popular software components before patches are applied.
To mitigate this risk, it is imperative for all organizations and individual users to update their Firefox installations immediately. The vulnerability has been addressed in the stable release of Firefox version 158 as well as in the Extended Support Release channels at versions 115.43 and 153.5. These updates include corrected boundary checks within the JavaScript engine that ensure memory accesses remain strictly within allocated limits. Administrators should enforce automatic update policies to minimize the window of exposure for their users. Additionally, while waiting for patch deployment, deploying browser security extensions or configuring strict content security policies can help reduce the attack surface by limiting the execution capabilities of untrusted scripts. Regular monitoring of vendor advisories and maintaining up-to-date software configurations remain critical components of a robust defense-in-depth strategy against such memory corruption vulnerabilities.