RUSTSEC-2020-0074: Reference counting error in `From<Py<T>>`

What to do

1. See which version you have: cargo tree -i pyo3 (it also shows which of your dependencies pulls it in).
2. Update within your version requirement: cargo update -p pyo3. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for example pyo3 = "0.12.4") 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

A bug in From<Py<T>> would lead to an extra reference count decrement, often leading to use-after-free issues.

References

• Package: crates.io/crates/pyo3
• Advisory: rustsec.org/advisories/RUSTSEC-2020-0074.html
• Web: github.com/PyO3/pyo3/pull/1297

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

Other advisories for pyo3

• VulnerabilityRUSTSEC-2024-0378 · 2024-10-12Risk of use-after-free in `borrowed` reads from Python weak references
• VulnerabilityRUSTSEC-2024-0409 · 2024-12-04Build corruption when using `PYO3_CONFIG_FILE` environment variable
• VulnerabilityRUSTSEC-2025-0020 · 2025-04-01Risk of buffer overflow in `PyString::from_object`
• VulnerabilityRUSTSEC-2026-0013 · 2026-02-18Type confusion when accessing data from sublasses of subclasses of native types with `abi3` feature targeting Python 3.12 and up
• VulnerabilityRUSTSEC-2026-0176 · 2026-06-11Out-of-bounds read in `nth` / `nth_back` for `PyList` and `PyTuple` iterators
• VulnerabilityRUSTSEC-2026-0177 · 2026-06-11Missing `Sync` bound on `PyCFunction::new_closure` closures

Full security history of pyo3