Summary
Workers for local Dask clusters mistakenly listened on public interfaces
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).
Impact
CVE-2021-42343 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2021.10.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2021-42343? CVE-2021-42343 is a critical-severity security vulnerability in distributed (pip), affecting versions >= 0, < 2021.10.0. It is fixed in 2021.10.0.
- How severe is CVE-2021-42343? CVE-2021-42343 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of distributed are affected by CVE-2021-42343? distributed (pip) versions >= 0, < 2021.10.0 is affected.
- Is there a fix for CVE-2021-42343? Yes. CVE-2021-42343 is fixed in 2021.10.0. Upgrade to this version or later.
- Is CVE-2021-42343 exploitable, and should I be worried? Whether CVE-2021-42343 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-42343 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-42343? Upgrade
distributedto 2021.10.0 or later.