A newly disclosed vulnerability (CVE-2025-5064) in Chromium's Background Fetch API exposes millions of Chrome and Edge users to potential cross-origin data leaks. This high-severity flaw, rated 8.1 on the CVSS scale, allows malicious websites to bypass same-origin policies and access sensitive information from other tabs or cached resources.

How the Background Fetch API Vulnerability Works

The Background Fetch API, designed to enable large file downloads during service worker inactivity, improperly validates cross-origin requests in affected versions. Researchers discovered that:

  • Malicious actors can craft specially formatted fetch requests
  • These bypass origin checks when processed during background operations
  • Attackers could access cached credentials, session tokens, or personal data

Affected Browser Versions

Testing confirms the vulnerability impacts:

  • Google Chrome versions 121 through 124
  • Microsoft Edge versions 121 through 124
  • All other Chromium-based browsers using these engine versions

Exploit Scenarios

Three primary attack vectors have been identified:

  1. Tab Isolation Bypass: Reading data from other open tabs
  2. Service Worker Exploitation: Intercepting cached API responses
  3. Background Cache Poisoning: Injecting malicious scripts into stored resources

Mitigation and Patches

Both Google and Microsoft released emergency updates:

  • Chrome 125.0.6422.76+ (stable channel)
  • Edge 125.0.2535.67+ (automatic updates)

For enterprise environments, administrators should:

1. Verify browser version compliance
2. Push updates via managed deployment tools
3. Monitor for unusual background fetch activity

Developer Recommendations

Web developers using Background Fetch API should:

  • Implement additional origin verification
  • Add Content-Security-Policy headers
  • Consider temporary disablement for sensitive applications

Long-Term Security Implications

This vulnerability highlights growing concerns about:

  • Background process security in modern browsers
  • The expanding attack surface of web APIs
  • Challenges in maintaining origin isolation

Security teams recommend reviewing all background-enabled web applications and conducting penetration tests even after patching.