CVE-2024-3856

What it actually does

Use-after-free condition during WebAssembly array creation when garbage collection interrupts execution, allowing memory corruption in the browser process.

Why it matters to the business

Attackers could execute arbitrary code or steal data from users running outdated browser versions, leading to compromised endpoints and potential data breaches across the user base.

How an attack unfolds

An attacker hosts a malicious webpage containing specially crafted WebAssembly code; when the victim visits the page, garbage collection during array creation triggers the use-after-free, enabling memory manipulation and code execution.

How to fix it

Update affected Firefox installations to version 125 or later as soon as possible; enable automatic updates where feasible and audit any embedded or enterprise-managed browser deployments.

How to confirm the fix worked

Verify browser version is 125 or higher; test WebAssembly execution paths under simulated garbage collection pressure in a controlled environment to confirm absence of the use-after-free condition.

Typical attack path

1. Attacker crafts and hosts malicious webpage with WebAssembly payload
2. Victim is lured to the page via phishing or compromised site
3. Browser loads and executes the WebAssembly module
4. Garbage collection interrupts array creation triggering the flaw
5. Attacker gains memory corruption primitive leading to code execution

How to detect it

Search browser process crash logs and telemetry for unexpected terminations during WebAssembly execution; review web proxy logs for access to suspicious domains hosting WebAssembly content around the time of any anomalous browser behavior.

What your security team should do

• Prioritize immediate browser updates for all endpoints given high CVSS and remote attack vector
• Monitor EPSS score for any upward trend indicating increased exploit likelihood
• Implement web filtering or browser isolation for high-risk user populations until patches are deployed
• Review internal web application usage of WebAssembly for similar patterns