Description

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.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-09-15T13:16:51.403Z",
  "pubdate": "2026-09-15T13:16:51.403Z",
  "executiveSummary": "A privilege escalation vulnerability exists within the Service Workers component of the Firefox browser DOM. This security flaw permits a local attacker to manipulate Service Worker operations to bypass standard security boundaries, potentially executing actions with elevated privileges. The vulnerability affects Firefox, Firefox ESR 115, Firefox ESR 140, and Firefox ESR 153 series. Successful exploitation allows for unauthorized interaction with the browser's internal logic, which may lead to cross-origin data access, persistent malicious script execution, or broader system-level impact depending on the context of the escalation. This vulnerability represents a significant risk to user integrity and data confidentiality, as Service Workers are designed to operate independently of the main browser thread. Exploitation typically requires the attacker to successfully deploy or influence a Service Worker registration process within the victim's browser environment. Users are strongly advised to update to the latest patched versions to eliminate the underlying logic error responsible for this privilege boundary breach.",
  "technicalDetails": "The vulnerability resides in the DOM (Document Object Model) implementation of Service Workers within the Firefox engine. Service Workers function as programmable network proxies, acting as intermediaries between the browser, the network, and the cache. The core issue involves a flaw in how the Service Worker interface manages internal security contexts and state transitions during worker registration or message passing.\nThe attack flow initiates when a malicious entity exploits the improper validation of Service Worker scope or origin constraints. By injecting specific JavaScript payloads into a compromised or malicious web context, an attacker can manipulate the lifecycle events of a Service Worker. In a standard exploitation scenario, the attacker registers a Service Worker that improperly interacts with the browser's internal APIs, effectively breaking the isolation between the worker's execution context and the primary document context. This bypasses the Same-Origin Policy (SOP) intended to protect user sessions.\nThe root cause is a failure in the internal security checks responsible for verifying the privilege level of the calling process when performing DOM-related Service Worker operations. This allows the Service Worker to perform actions that are traditionally reserved for higher-privileged browser components. Once the escalation is triggered, the attacker gains the ability to intercept or modify network requests, access restricted storage (such as IndexedDB or Cache API) across origins, or execute code with the privilege of the browser's background processes.\nAffected versions include Firefox 156, Firefox ESR 115.41, Firefox ESR 140.16, and Firefox ESR 153.3. The vulnerability does not require authentication from the victim, provided they navigate to a malicious URL or interact with a compromised web page that triggers the Service Worker registration sequence. Post-exploitation impact ranges from sensitive data exfiltration—such as cookies and authorization tokens—to persistent cross-site scripting (XSS) attacks that remain active even after the initial page is closed, due to the background persistence nature of Service Workers.\nThe technical mitigation requires ensuring strict adherence to the origin-based security boundaries during the Service Worker message-handling loop, ensuring that the IPC (Inter-Process Communication) mechanisms between the browser kernel and the Service Worker thread perform rigorous origin validation before committing any requested state changes."
}