Affected versions of the crate had a Send/Sync implementation for MappedMutexGuard that only considered variance on T, while MappedMutexGuard dereferenced to U.
This could of led to data races in safe Rust code when a closure used in MutexGuard::map() returns U that is unrelated to T.
The issue was fixed by fixing Send and Sync implementations, and by adding a PhantomData<&'a mut U> marker to the MappedMutexGuard type to tell the compiler that the guard is over U too.
{ "nvd_published_at": "2020-12-31T09:15:00Z", "cwe_ids": [ "CWE-362" ], "severity": "MODERATE", "github_reviewed": true, "github_reviewed_at": "2022-06-16T23:55:12Z" }