---
id: CVE-2021-42343
aliases:
  - GHSA-hwqr-f3v9-hwxr
  - GHSA-j8fq-86c5-5v2r
  - PYSEC-2021-387
  - PYSEC-2021-871
  - PYSEC-2021-872
title: Workers for local Dask clusters mistakenly listened on public interfaces
summary: Workers for local Dask clusters mistakenly listened on public interfaces
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
vendor: distributed
product: distributed
ecosystem: pip
affected:
  - distributed < 2021.10.0
patched:
  - distributed 2021.10.0
published: '2022-07-15'
updated: '2026-07-08'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-hwqr-f3v9-hwxr'
references:
  - url: >-
      https://github.com/dask/distributed/security/advisories/GHSA-hwqr-f3v9-hwxr
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2021-42343'
  - url: 'https://github.com/dask/distributed/pull/5427'
  - url: >-
      https://github.com/dask/distributed/commit/afce4be8e05fb180e50a9d9e38465f1a82295e1b
  - url: 'https://docs.dask.org/en/latest/changelog.html'
  - url: 'https://github.com/dask/dask/tags'
  - url: 'https://github.com/dask/distributed'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/distributed/PYSEC-2021-871.yaml
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/distributed/PYSEC-2021-872.yaml
tags:
  - osv
  - pip
epss: 0.02995
epssPercentile: 0.86786
ingestedAt: '2026-07-08T18:25:50.334Z'
---

## Overview

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

- `distributed < 2021.10.0`

## Remediation

Upgrade to a patched release:

- `distributed 2021.10.0`