The vulnerability stems from unconditional implementation of Send/Sync traits in AtomicBox. The pre-patch code (unsafe impl<T: Sized> Sync/Send) lacked required bounds, violating Rust's thread safety guarantees. This allowed dangerous cross-thread sharing of types like Cell (which isn't Sync) and Rc (which isn't Send), enabling data races. The commit diff explicitly shows these trait implementations being modified to add T: Sync/Send bounds, confirming these were the vulnerable components. The added compile-fail test further validates that improper usage is now prevented.