CVE-2026-100807 in Firefox
Summary
by MITRE • 09/29/2026
Privilege escalation in the DOM: Service Workers component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, and Firefox ESR 140.17.
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Analysis
by VulDB Data Team • 09/29/2026
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 issue allows an attacker to bypass intended security restrictions by leveraging improper access control mechanisms inherent in how service workers interact with browser contexts and DOM elements. The core technical deficiency lies in the insufficient validation of permissions when a service worker attempts to manipulate or inspect DOM nodes that are typically restricted from cross-origin or untrusted script execution. By exploiting this gap, an attacker can elevate their privileges within the browser environment, effectively gaining access to sensitive data or functionality that should remain isolated behind security boundaries such as same-origin policies and sandboxing constraints.
From a technical perspective, service workers act as proxy scripts between web applications and the network, enabling features like offline caching and push notifications. However, when these workers are granted excessive privileges over DOM operations without adequate verification of their origin or intent, they can be manipulated to perform actions outside their designated scope. The flaw likely involves a race condition or an incomplete state check where the browser fails to properly enforce context isolation during specific lifecycle events of the service worker registration or activation process. This allows malicious scripts embedded in a webpage to trigger privileged operations through the compromised service worker interface, effectively breaking out of the sandboxed environment intended for web content execution.
The operational impact of this vulnerability is severe, as it undermines the fundamental trust model of modern web browsers. An attacker who successfully exploits this flaw can potentially access sensitive user data stored within the DOM, such as authentication tokens, personal information, or session cookies that are not properly secured against script-based extraction. Furthermore, the ability to escalate privileges enables further attacks including cross-site scripting amplification, where the compromised service worker is used to inject malicious payloads into other tabs or windows under different security contexts. This can lead to full account takeover, data exfiltration, and the establishment of persistent footholds within user sessions that are difficult for traditional detection mechanisms to identify due to their origin from legitimate browser components.
This vulnerability aligns with CWE-269 Improper Privilege Management, as it involves a failure to enforce proper authorization levels during critical operations. Additionally, it relates to CWE-749 Exposed Dangerous Method in the context of exposing internal APIs or methods that should remain restricted to privileged contexts. In terms of offensive security frameworks, this exploit technique corresponds to ATT&CK T1053 Scheduled Task/Job which can be adapted for persistence via service worker registration, and potentially T1087 Account Discovery if used to enumerate user information within the DOM structure. The exploitation path typically involves crafting a malicious webpage that registers a compromised service worker designed to intercept or manipulate DOM interactions in ways that bypass standard security checks.
Mitigation strategies primarily rely on applying the vendor-provided patches released for Firefox ESR 153.4, Firefox 157, and Firefox ESR 140.17 immediately upon deployment within organizational environments. For users unable to update instantly, implementing strict Content Security Policy directives can help mitigate some aspects of DOM manipulation by restricting script sources and enforcing nonce-based execution controls. Additionally, disabling service workers for untrusted sites through browser configuration or enterprise policies reduces the attack surface significantly. Organizations should also monitor for unusual network traffic patterns associated with new service worker registrations from unknown origins and ensure that endpoint detection systems are configured to flag anomalous behavior in web rendering processes. Regular security awareness training regarding phishing attempts designed to trigger such exploits remains a vital complementary defense layer alongside technical controls.