CVE-2026-74956 in Firefox
Summary
by MITRE • 08/18/2026
Same-origin policy bypass in the DOM: Service Workers component. This vulnerability was fixed in Firefox 154 and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/18/2026
The identified vulnerability represents a critical breach of the Same-Origin Policy within the Document Object Model, specifically affecting the service workers subsystem in Mozilla Firefox browsers. The same-origin policy is a fundamental security mechanism that restricts how a document or script loaded from one origin can interact with resources from another origin. By bypassing this restriction through the DOM manipulation capabilities exposed by service workers, an attacker could potentially access sensitive data belonging to other web applications running on different origins but served via the same browser instance. This flaw undermines the isolation guarantees that are essential for maintaining confidentiality and integrity across multiple concurrent web sessions within a single user agent environment.
Service workers act as network proxies sitting between web applications and the network, enabling features such as offline experiences, push notifications, and background sync operations. However, this powerful capability also expands the attack surface if not properly sandboxed against cross-origin data leakage. In this specific instance, the implementation allowed scripts to manipulate DOM elements in a way that circumvented origin checks intended for service worker contexts. This likely involved improper validation of context boundaries when handling messages or events dispatched between different origins through shared service worker interfaces. The technical flaw suggests that the browser failed to enforce strict separation rules during certain asynchronous operations or message passing sequences, allowing malicious code embedded in one site to read or modify state associated with another trusted site.
The operational impact of this vulnerability is severe for users who visit multiple websites simultaneously, particularly those involving financial transactions, email access, or administrative portals. An attacker could craft a malicious webpage that exploits the DOM manipulation flaw to steal session tokens, personal identifiable information, or other sensitive content from adjacent tabs or windows running different origins. This type of cross-origin data exfiltration can lead to account takeover, identity theft, and unauthorized actions performed under the victim's credentials. Since service workers often persist beyond the lifecycle of a single page visit, the vulnerability could also facilitate long-term surveillance or persistent access if the malicious script successfully registers itself as a background worker for a targeted domain.
Mitigation strategies primarily rely on applying the software updates released by Mozilla to address this specific code path deficiency. Users must upgrade to Firefox version 154 or later, which includes patches that reinforce origin checks within the service worker DOM interaction layer. For enterprise environments utilizing extended support releases, upgrading to Firefox ESR 153.1 is mandatory to ensure continued protection against these exploitation techniques. Additionally, organizations should enforce strict content security policies and disable unnecessary service worker registrations where not required for business operations. Regular monitoring of browser update notifications and automated patch management systems are essential components of a defense-in-depth strategy to prevent exposure to such high-severity client-side vulnerabilities.
This incident aligns with common vulnerability classifications found in industry standards, particularly CWE-200 which covers information exposure through improper access controls, and potentially CWE-841 regarding improper enforcement of same-origin policy. From an offensive security perspective as mapped by the MITRE ATT&CK framework, this behavior corresponds to techniques involving client-side protocol manipulation or data exfiltration via browser APIs. Understanding these mappings helps security teams prioritize remediation efforts based on established threat models and ensures that future development cycles incorporate stricter validation logic for cross-origin interactions within privileged browser components like service workers.