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MEDIUM severity

CVE-2021-38191 — tokio

MEDIUM

CVE-2021-38191 is a medium-severity (CVSS 5.9) CWE-362 vulnerability in tokio. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for tokio — see the affected versions and patch details below.

Race condition in tokio

Also known asGHSA-2grh-hm3w-w7hvRUSTSEC-2021-0072
Published
Updated
Affected
4 pkgs
Patched
4 / 4
Exploits
1 known
Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
0.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs58th percentile — riskier than 58% of all scored CVEsHighest risk
0.00%0.45%0.89%1.34%0.3%0.8%May 26Sep 26Nov 26

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

4 pkgs affected
🦀tokio🦀tokio🦀tokio🦀tokio

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

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

4 total 4 fixed
EcosystemPackageVulnerable rangeFix
🦀crates.iotokio≥ 1.8.0&&< 1.8.11.8.1cargo update -p tokio --precise 1.8.1
🦀crates.iotokio≥ 1.7.0&&< 1.7.21.7.2cargo update -p tokio --precise 1.7.2
🦀crates.iotokio≥ 1.6.0&&< 1.6.31.6.3cargo update -p tokio --precise 1.6.3
🦀crates.iotokio≥ 0.3.0&&< 1.5.11.5.1cargo update -p tokio --precise 1.5.1

Affected Products

1 product · 4 configurations
Application
tokiotokio
≥ 1.7.0 && < 1.7.2
1 version
1.8.0
Exploits & PoCs
1

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

An issue was discovered in the tokio crate before 1.8.1 for Rust. Upon a…

rustsec.orgNVDAug 2021

Detection & mitigation playbook

Open-source dependency

  1. Detect

    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.

  2. 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.

  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

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.
O3 Security · Impact-Aware SCA

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CVE-2021-38191: tokio — Fixed in 1.8.1