CVE-2026-109717 in Firefox
Summary
by MITRE • 10/13/2026
Use-after-free in the DOM: Bindings (WebIDL) component. This vulnerability was fixed in Firefox 158 and Firefox ESR 153.5.
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Analysis
by VulDB Data Team • 10/15/2026
The identified vulnerability represents a critical memory management error within the Document Object Model bindings, specifically involving the Web IDL implementation layer of Mozilla-based browsers such as Firefox. A use-after-free condition occurs when software continues to reference a memory location after it has been deallocated or freed by the system. In this specific context, the flaw resides in how JavaScript objects are mapped to C++ DOM interfaces through the WebIDL binding mechanism. When an object is garbage collected and its underlying native memory is released, subsequent operations that attempt to access properties or methods of that now-invalidated object can trigger undefined behavior. This type of vulnerability is particularly dangerous because it allows for arbitrary code execution if an attacker can carefully craft a sequence of events that forces the browser to use the freed memory before it has been reallocated for another purpose.
From a technical perspective, this flaw highlights the complexity inherent in bridging high-level scripting languages like JavaScript with low-level systems programming languages such as C++. The WebIDL specification defines how web APIs are exposed to scripts, and the binding code is responsible for managing the lifecycle of these objects. If the reference counting or garbage collection logic fails to properly synchronize between the script engine and the native DOM implementation, a race condition or logical error can leave a dangling pointer active in memory. An attacker could exploit this by creating a scenario where an object is destroyed while still being referenced by another part of the page, such as through asynchronous callbacks or event handlers that persist beyond the lifecycle of their associated elements. This allows for precise control over what data resides at the freed memory address, potentially leading to information disclosure or remote code execution depending on how the browser handles subsequent reads and writes to that location.
The operational impact of this vulnerability is severe, as it directly compromises the security boundary between untrusted web content and the host operating system. Successful exploitation could allow a malicious website to execute arbitrary commands with the privileges of the user running the browser. This undermines core web security principles such as same-origin policy isolation, potentially enabling attackers to steal sensitive data like cookies, session tokens, or personal information stored in local storage. Furthermore, it can facilitate drive-by download attacks where malware is silently installed on the victim's machine without any interaction beyond visiting a compromised webpage. The severity is amplified by the fact that DOM manipulation and JavaScript execution are fundamental activities for modern web applications, making this vulnerability applicable to a vast array of websites and services.
In terms of industry classification standards, this flaw aligns with CWE-416, which describes Use After Free vulnerabilities where memory is accessed after it has been freed. It also relates closely to CWE-362 regarding Concurrent Execution using Shared Resource with Improper Synchronization if the issue stems from a race condition during object lifecycle management. From an offensive security perspective, this vulnerability maps to MITRE ATT&CK technique T1059, specifically Command and Scripting Interpreter subcategories like JavaScript or ECMAScript, as it leverages script execution for exploitation. It also falls under Defense Evasion techniques such as Obfuscated Files or Information if the exploit code is designed to evade detection by security software through complex memory manipulation patterns.
Mitigation strategies primarily involve applying the vendor-provided patches that address these specific binding logic errors. For end-users, this means ensuring that Firefox 158 and Firefox Extended Support Release (ESR) version 153.5 or later are installed to benefit from the corrected memory management routines. Organizations should enforce automated patching policies for all browser endpoints within their infrastructure to minimize exposure windows. Additionally, developers building web applications can reduce risk by implementing strict Content Security Policy headers that restrict inline script execution and limit external resource loading, thereby reducing the attack surface available to potential exploit attempts. While no technical workaround exists at the application level due to the nature of the vulnerability being in the browser engine itself, maintaining up-to-date software remains the most effective defense against this class of memory corruption flaws.