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Not in CISA KEV
HIGH severity

CVE-2019-16141 — once_cell

HIGHFix: matklad/once_cell#47

CVE-2019-16141 is a high-severity (CVSS 7.5) Improper Input Validation vulnerability in once_cell. A fix is available for once_cell — see the affected versions and patch details below.

Improper Input Validation in once_cell

Also known asGHSA-7j44-fv4x-79g9RUSTSEC-2019-0017
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.6%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs75th percentile — riskier than 75% of all scored CVEsHighest risk
0.00%0.69%1.39%2.08%0.3%1.6%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2019-16141 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
🦀once_cell

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.

Description

If during the first dereference of Lazy 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.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🦀crates.ioonce_cell≥ 0.2.5&&< 1.0.11.0.1cargo update -p once_cell --precise 1.0.1

Affected Products

1 product · 1 configurations
Application
once cellonce_cell_project
≥ 0.2.6 && < 1.0.1
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for once_cell, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update once_cell to 1.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2019-16141 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

If during the first dereference of Lazy 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.
O3 Security · Impact-Aware SCA

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CVE-2019-16141: once_cell — Fixed in 1.0.1