Rust's borrow checker has been unsound since version 1.4, a new bug report reveals

11 year old unsoundness bugs found in Rust borrow checker

A GitHub issue filed by jsnell shows that Rust's lifetime requirements can be bypassed through covariant field assignment. A struct with a 'static bound can be handed a non-'static reference, letting Drop code treat a dangling pointer as valid. The bug compiles on stable releases back to 1.4, and ASan flags a stack-use-after-scope. Rust maintainers have labeled it I-unsound and P-high.