In JsRuntimeState::setCaller, it saves the current caller in the JsRuntimeState object(rcx+158h in 64-bit). But the garbage collector doesn't mark this saved value. So it results in a UAF.
Unlike in our test environment(Linux), it doesn't make reliable crashes on Windows. So I used another bug(#1258) to confirm the bug. If the UAF bug doesn't exist, the "crash" function will not be called(See poc.js).
The password of the zip file is "calleruaf"
Proof of Concept: