The vulnerability stems from ObjectPool methods assuming HandleLike trait methods (index()/version()) are pure/constant. The get and get_mut methods first check handle validity via contains(), then immediately use handle.index() in unsafe array accesses. A malicious HandleLike implementation could return different values between these operations, leading to out-of-bounds memory access. The Drop implementation also uses handle.index() without validation, but the primary attack surface is in the get/get_mut methods that combine safety checks with subsequent unsafe accesses based on potentially changing handle values.