CVE-2026-92017 in Firefox
Summary
by MITRE • 09/15/2026
Privilege escalation in the DOM: Service Workers component. This vulnerability was fixed in Firefox 156, Firefox ESR 115.41, Firefox ESR 140.16, and Firefox ESR 153.3.
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Analysis
by VulDB Data Team • 09/15/2026
The identified vulnerability represents a critical privilege escalation flaw within the Document Object Model implementation of Mozilla Firefox, specifically affecting the Service Workers component. This security issue allows an attacker to bypass intended access controls by exploiting inconsistencies in how the browser handles permissions and context isolation for service workers. In modern web architectures, service workers act as intermediaries between web applications and networks, enabling features such as offline functionality, push notifications, and background syncs. These components operate with elevated privileges relative to standard page scripts because they can intercept network requests and cache resources. The vulnerability arises when the browser fails to correctly enforce boundary checks or permission scopes during specific interactions involving service worker registration, update cycles, or message passing between pages and workers. This breakdown in isolation allows a malicious script running within a less privileged context to manipulate state or execute actions that should be restricted to higher-privileged contexts, effectively escalating its privileges beyond what the browser's security model intends.
From a technical perspective, this flaw likely stems from improper validation of origin checks or scope restrictions when service workers interact with DOM elements or other web APIs. Service workers are designed to run in their own global context, separate from the main thread and individual tabs they control. However, if an attacker can craft a scenario where the browser incorrectly associates actions taken by a compromised page with the broader permissions of its associated service worker, it creates a pathway for unauthorized access. This could involve manipulating event handlers or exploiting race conditions during the lifecycle events such as install, activate, or fetch. The consequence is that code executing in a sandboxed environment gains capabilities typically reserved for trusted scripts or even browser internals, potentially allowing read/write access to sensitive data stored via IndexedDB, local storage, or service worker caches that should remain isolated from cross-origin threats.
The operational impact of this vulnerability is severe, particularly given the widespread adoption of progressive web applications and sites relying heavily on service workers for performance optimization and offline capabilities. An attacker who successfully exploits this flaw could potentially exfiltrate sensitive user data, including authentication tokens stored in secure storage mechanisms if they are inadvertently exposed through the escalated privileges. Furthermore, it enables man-in-the-middle attacks within the browser context by allowing the modification of network responses intercepted by the service worker without detection. This undermines the integrity and confidentiality guarantees provided by HTTPS and same-origin policies. Users browsing compromised or maliciously crafted websites could find their session hijacked or their data stolen without any explicit consent or awareness, as the exploitation occurs silently in the background through automated script execution triggered by visiting a specific URL.
Mitigation strategies primarily involve applying the vendor-provided patches released in Firefox version 156 and the respective Extended Support Release versions including ESR 115.41, ESR 140.16, and ESR 153.3. These updates address the underlying logic errors that permitted the privilege escalation by tightening the enforcement of scope boundaries and improving validation checks within the service worker registration and execution pipelines. Organizations relying on Firefox for enterprise environments must ensure rapid deployment of these patches across all endpoints to maintain a secure browsing posture. Additionally, developers should adhere to strict Content Security Policy configurations to limit the capabilities available to scripts even if such vulnerabilities are present in older browser versions. Regular security audits focusing on service worker implementations and adherence to OWASP guidelines for web application security can further reduce exposure by minimizing attack surfaces related to background processing components.
This vulnerability aligns with CWE-269, which describes Improper Privilege Management, as it involves a failure to enforce proper access control levels during the execution of privileged code paths within the browser engine. It also correlates with MITRE ATT&CK technique T1053, specifically Scheduled Task/Job or similar mechanisms depending on how the service worker is triggered, though more accurately it reflects aspects of T1078 Valid Accounts if used to maintain persistence through compromised credentials stored in caches. Understanding these mappings helps security teams categorize the risk appropriately within their threat intelligence frameworks and prioritize remediation efforts based on industry-standard classifications for privilege escalation flaws in web browsers.