An issue was discovered in the beef crate before 0.5.0 for Rust.
Affected versions of this crate did not have a T: Sync bound in the Send impl for Cow<'_, T, U>. This allows users to create data races by making Cow contain types that are (Send && !Sync) like Cell<_> or RefCell<_>.

Such data races can lead to memory corruption.

The flaw was corrected in commit d1c7658 by adding trait bounds T: Sync and T::Owned: Send to the Send impl for Cow<'_, T, U>.

References

• https://nvd.nist.gov/vuln/detail/CVE-2020-36442
• https://rustsec.org/advisories/RUSTSEC-2020-0122.html
• maciejhirsz/beef#37
• https://raw.githubusercontent.com/rustsec/advisory-db/main/crates/beef/RUSTSEC-2020-0122.md