RUSTSEC-2023-0070: Insufficient covariance check makes self_cell unsound

What to do

1. See which version you have: cargo tree -i self_cell (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p self_cell. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example self_cell = "1.0.2") or update the dependency that pulls it in.
3. Check again with cargo audit, or paste your Cargo.lock into our Cargo.toml checker.

Details from the advisory

All public versions prior to 1.02 used an insufficient check to ensure that users correctly marked the dependent type as either covariant or not_covariant. This allowed users to mark a dependent as covariant even though its type was not covariant but invariant, for certain invariant types involving trait object lifetimes. One example for such a dependent type is type Dependent<'a> = RefCell<Box<dyn fmt::Display + 'a>>. Such a type allowed unsound usage in purely safe user code that leads to undefined behavior. The patched versions now produce a compile time error if such a type is marked as covariant.

References

• Package: crates.io/crates/self_cell
• Advisory: rustsec.org/advisories/RUSTSEC-2023-0070.html
• Report: github.com/Voultapher/self_cell/issues/49

From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.