Three removal and replacement paths destroy an initialized value before committing the metadata change that removes it. Destruction runs T::drop(), which is user code and may panic. If it does, the commit is skipped and the container still claims ownership of the already-destroyed value, so its own destructor drops that value a second time.

Stack::pop drops the top value before reducing next ofs. Stack's destructor pops in a loop, so an unchanged next ofs re-drops the same value.

Fifo::pop front (via pop front inner) drops the front value before advancing read pos. An unchanged read pos still points at the destroyed value.

Value::replace stable drops the existing value before writing the replacement. If the destructor panics the replacement is never written, but the backing storage still holds the old value's metadata.

This is separate from RUSTSEC-2021-0033, which covered a clone panic on insertion in push cloned and was fixed in 0.6.1.

A heap-owning value is freed twice, corrupting the allocator. Reachable from safe Rust with any element type whose Drop can panic — no unsafe on the caller's side.

Confirmed under AddressSanitizer, which reports attempting double-free on all three paths.

Fixed in 0.8.2.