CVE-2016-5287

What it actually does

Use-after-free during actor destruction involving service workers leads to memory corruption that can be leveraged for arbitrary code execution.

Why it matters to the business

Attackers could remotely compromise user systems running vulnerable Firefox versions, resulting in data theft, malware installation, or loss of control over affected endpoints.

How an attack unfolds

An attacker hosts a malicious page that loads a service worker; when the worker's actor is destroyed, a dangling reference is reused to corrupt memory and gain code execution in the browser process.

How to fix it

Upgrade all instances of Mozilla Firefox to version 49.0.2 or later; disable service workers via enterprise policy if immediate patching is impossible.

How to confirm the fix worked

Verify installed Firefox version is 49.0.2 or newer; review browser crash reports for service-worker actor destruction signatures and confirm absence of related memory-corruption indicators.

Typical attack path

1. Host or compromise a webpage that registers a service worker
2. Trigger navigation or worker lifecycle events that initiate actor destruction
3. Reuse the freed object to achieve memory corruption
4. Execute arbitrary code within the browser sandbox or escape it

How to detect it

Examine browser crash logs and telemetry for service-worker actor destruction events; correlate web proxy logs with known exploit delivery domains; review endpoint process creation anomalies following browser activity.

What your security team should do

• Immediately deploy Firefox 49.0.2+ across the environment
• Block known malicious domains associated with historical service-worker exploits at the proxy or firewall
• Enable enterprise update enforcement and audit for any remaining pre-49.0.2 instances