CVE-2026-117963 in Firefox
Summary
by MITRE • 10/27/2026
Incorrect boundary conditions in the DOM: Service Workers component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability resides within the Service Workers implementation of Mozilla Firefox, specifically involving incorrect boundary condition handling during Document Object Model operations. Service workers act as a proxy between web applications and the network, enabling features such as offline caching, push notifications, and background synchronization. The flaw arises when the browser fails to properly validate or constrain input parameters related to DOM interactions within this component. This lack of rigorous boundary checking allows for potential memory corruption or logic errors that can be exploited by maliciously crafted web content. Such issues typically stem from off-by-one errors, integer overflows, or improper array indexing where the software does not correctly verify if an index falls within the allocated memory bounds before accessing it.
From a technical perspective, this type of vulnerability is commonly classified under CWE-125 Out-of-bounds Read or CWE-787 Out-of-bounds Write depending on whether the exploit attempts to read sensitive data from adjacent memory locations or overwrite critical program structures. The presence of such flaws in high-level components like Service Workers highlights the complexity involved in managing asynchronous operations and cross-origin resource sharing contexts securely. When boundary conditions are not strictly enforced, an attacker can potentially trigger undefined behavior within the browser engine. This could lead to crashes that disrupt service availability or more severe consequences if the memory corruption allows for arbitrary code execution. The exploitation of this flaw would likely require a victim to visit a specially crafted webpage designed to manipulate the Service Worker registration or message handling processes in a way that triggers the incorrect boundary check.
The operational impact of this vulnerability is significant due to its potential to compromise browser stability and security posture. If successfully exploited, it could allow an attacker to bypass same-origin policies, access sensitive data stored within service worker caches, or execute arbitrary code on the user's machine by leveraging memory corruption techniques such as heap spraying or ROP chains in conjunction with other vulnerabilities. This undermines the trust model of web applications that rely on Service Workers for secure background operations. Users relying on Firefox for critical tasks involving financial transactions, sensitive communications, or corporate data access are at risk if they encounter malicious sites designed to exploit this specific flaw. The vulnerability affects both standard releases and extended support versions, indicating a systemic issue in the underlying engine logic rather than an isolated incident.
To mitigate these risks, users must ensure their browsers are updated to Firefox version 159 or later, as well as Firefox ESR 153.6 or newer, where this specific boundary condition error has been corrected by Mozilla engineers. These updates include patches that enforce stricter validation checks on DOM interactions within the Service Worker context, ensuring that all indices and offsets remain within valid memory ranges. Additionally, security administrators should monitor for any signs of browser instability or unexpected network behavior associated with service worker activities. Implementing content security policies that restrict the use of certain APIs can also provide an additional layer of defense against exploitation attempts. Regular patch management is essential to maintain a secure browsing environment and prevent attackers from leveraging known flaws in widely used web technologies.