CVE-2021-38191 — tokio
MEDIUMCVE-2021-38191 is a medium-severity (CVSS 5.9) CWE-362 vulnerability in tokio. 1 public exploit reference exists, so weaponization risk is real. A fix is available for tokio — see the affected versions and patch details below.
Race condition in tokio
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-38191 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
tokio🦀tokio🦀tokio🦀tokioReal-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
When aborting a task with JoinHandle::abort, the future is dropped in the thread calling abort if the task is not currently being executed. This is incorrect for tasks spawned on a LocalSet. This can easily result in race conditions as many projects use Rc or RefCell in their Tokio tasks for better performance.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | tokio | ≥ 1.8.0&&< 1.8.1 | 1.8.1cargo update -p tokio --precise 1.8.1 |
| 🦀crates.io | tokio | ≥ 1.7.0&&< 1.7.2 | 1.7.2cargo update -p tokio --precise 1.7.2 |
| 🦀crates.io | tokio | ≥ 1.6.0&&< 1.6.3 | 1.6.3cargo update -p tokio --precise 1.6.3 |
| 🦀crates.io | tokio | ≥ 0.3.0&&< 1.5.1 | 1.5.1cargo update -p tokio --precise 1.5.1 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for tokio, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update tokio to 1.8.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-38191 is resolved across your whole dependency graph.
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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-38191 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-38191. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-38191 in your dependencies?
O3 Security finds CVE-2021-38191 across crates.io dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.