CVE-2016-1949

What it actually does

Bypasses Same Origin Policy restrictions by allowing improper interaction between Service Workers and NPAPI plugins, enabling spoofed responses to cross-origin requests such as those for crossdomain.xml files.

Why it matters to the business

Attackers can access or manipulate data across domain boundaries in affected browsers, increasing risk of data theft or unauthorized actions on user systems until patched.

How an attack unfolds

An attacker hosts a malicious site that registers a Service Worker; the worker issues plugin-handled requests to a target domain, and the attacker spoofs responses to bypass SOP checks, achieving cross-origin data access or actions.

How to fix it

Upgrade Mozilla Firefox to version 44.0.2 or later to enforce proper Service Worker and plugin isolation.

How to confirm the fix worked

Verify installed Firefox version is 44.0.2 or newer; test with crafted cross-origin Service Worker scenarios to confirm SOP enforcement.

Typical attack path

1. Victim visits attacker-controlled website
2. Site registers a Service Worker to intercept and manipulate requests
3. Worker triggers NPAPI plugin requests for cross-origin resources
4. Attacker spoofs responses to evade Same Origin Policy enforcement
5. Browser processes responses as if from the legitimate origin

How to detect it

Review browser version logs and update histories for pre-44.0.2 instances; inspect web proxy or endpoint logs for unusual Service Worker registrations followed by cross-origin plugin activity.

What your security team should do

• Prioritize browser updates across all endpoints within 30 days given the high CVSS score
• Monitor for any remaining pre-44.0.2 deployments via inventory scans
• Educate users on prompt browser updates to reduce exposure window