CVE-2021-42343 is a critical-severity (CVSS 9.8) remote code execution vulnerability in distributed. A fix is available for distributed — see the affected versions and patch details below.
Workers for local Dask clusters mistakenly listened on public interfaces
EPSS Exploitation Probability
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
distributedReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Versions of distributed earlier than 2021.10.0 had a potential security vulnerability relating to single-machine Dask clusters.
Clusters started with dask.distributed.LocalCluster or dask.distributed.Client() (which defaults to using LocalCluster) would mistakenly configure their respective Dask workers to listen on external interfaces (typically with a randomly selected high port) rather than only on localhost. A Dask cluster created using this method AND running on a machine that has these ports exposed could be used by a sophisticated attacker to enable remote code execution. Users running on machines with standard firewalls in place, or using clusters created via cluster objects other than LocalCluster (e.g. dask_kubernetes.KubeCluster) should not be affected. This vulnerability is documented in CVE-2021-42343, and was fixed in version 2021.10.0 (PR #5427).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | distributed | all versions | 2021.10.0pip install --upgrade 'distributed==2021.10.0' |
Affected Products
daskanacondaDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for distributed, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update distributed to 2021.10.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-42343 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.
Frequently Asked Questions
Is CVE-2021-42343 in your dependencies?
Find it across PyPI, including transitive dependencies.