Rust advisories / once_cell
Vulnerability HighRUSTSEC-2019-0017 · once_cell
RUSTSEC-2019-0017: Panic during initialization of Lazy<T> might trigger undefined behavior
Short answerA security vulnerability in the once_cell crate: Panic during initialization of Lazy<T> might trigger undefined behavior. High severity (CVSS 7.5). Fixed in 1.0.1: update to a fixed version.
| Crate | once_cell |
|---|---|
| Type | Vulnerability |
| Affected versions | From 0.2.5 before 1.0.1. |
| Fixed in | 1.0.1 |
| Severity | High, CVSS 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| Published | 2019-09-01 |
| Last changed | 2023-11-08 |
| Also known as | CVE-2019-16141, GHSA-7j44-fv4x-79g9 |
| Affected functions | once_cell::sync::Lazy::deref, once_cell::sync::Lazy::force, once_cell::unsync::Lazy::deref, once_cell::unsync::Lazy::force |
What to do
- See which version you have:
cargo tree -i once_cell(it also shows which of your dependencies pulls it in). - Update within your version requirement:
cargo update -p once_cell. If the fix is a newer major or minor than your requirement allows, raise it in Cargo.toml (for exampleonce_cell = "1.0.1") or update the dependency that pulls it in. - Check again with
cargo audit, or paste your Cargo.lock into our Cargo.toml checker.
Details from the advisory
If during the first dereference of Lazy<T> the initialization function panics, subsequent dereferences will execute std::hints::unreachable_unchecked.
Applications with panic = "abort" are not affected, as there will be no subsequent dereferences.
References
- Package: crates.io/crates/once_cell
- Advisory: rustsec.org/advisories/RUSTSEC-2019-0017.html
- Report: github.com/matklad/once_cell/issues/46
From the RustSec Advisory Database (CC0-1.0) via the OSV export, downloaded Oct 24, 2026. Severity score computed from the published CVSS vector.
Up next
Are you affected?Check your whole dependency treePaste Cargo.lock: every advisory, for your exact versions.Read it next →Also worth your time
Did this answer your question?