CVE-2019-9810

What it actually does

Incorrect alias information in IonMonkey JIT compiler for Array.prototype.slice causes missing bounds checks, resulting in a buffer overflow that corrupts memory and can lead to arbitrary code execution.

Why it matters to the business

Unpatched systems remain exposed to remote compromise years after disclosure, potentially allowing data theft, persistent access, or malware deployment across widely deployed browser and email clients in enterprise environments.

How an attack unfolds

An attacker hosts a malicious webpage containing crafted JavaScript that invokes Array.prototype.slice under conditions triggering the JIT alias flaw; when the victim loads the page the missing bounds check permits buffer overflow, enabling shellcode injection and remote code execution.

How to fix it

Upgrade Mozilla Firefox to 66.0.1 or newer, Firefox ESR to 60.6.1 or newer, and Thunderbird to 60.6.1 or newer; apply equivalent patches from Red Hat or other distributors for affected enterprise packages.

How to confirm the fix worked

Confirm installed versions meet or exceed the fixed releases listed above; re-test with known proof-of-concept JavaScript triggers in a lab environment to verify absence of the alias error.

Typical attack path

1. Attacker prepares malicious webpage embedding exploit JavaScript targeting IonMonkey
2. Victim is lured to the page via phishing or compromised site
3. Browser JIT compiles the slice operation with incorrect alias data
4. Bounds check is elided, allowing out-of-bounds write
5. Attacker gains memory corruption primitive and achieves code execution

How to detect it

Review browser process crash logs and JIT compiler telemetry for anomalous slice-related faults; inspect web proxy or endpoint logs for visits to domains hosting known exploit kits that target this class of JIT memory corruption.

What your security team should do

• Immediately inventory and update all Firefox, ESR, and Thunderbird instances across the environment
• Block or sandbox legacy unpatched browser versions via enterprise policy
• Monitor EPSS trend and exploit availability for any renewed campaign activity
• Include browser update status in regular vulnerability scanning and patch compliance reporting