CVE-2021-21865

Name: CVE-2021-21865
Creator: NVD / NIST
Published: 2021-08-02T21:15:07.973+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.8/10EPSS 1.30%

Last modified Jun 17, 2026

CVE-2021-21865 is a high-severity vulnerability rated 7.8/10 on the CVSS scale. A unsafe deserialization vulnerability exists in the PackageManagement.plugin ExtensionMethods.Clone() functionality of CODESYS GmbH CODESYS Development System 3.5.16. A specially crafted file can lead to arbitrary command execution. EPSS estimates a 1.30% chance of exploitation in the next 30 days.

Description

A unsafe deserialization vulnerability exists in the PackageManagement.plugin ExtensionMethods.Clone() functionality of CODESYS GmbH CODESYS Development System 3.5.16. A specially crafted file can lead to arbitrary command execution. An attacker can provide a malicious file to trigger this vulnerability.

Metrics

CVSS 3.1

7.8/10

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS Probability

1.30%

66.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Codesys	Development System	3.5.16.0
Codesys	Development System	3.5.17.0

References

https://customers.codesys.com/index.php?eID=dumpFile&t=f&f=16805&token=ee583c498941d9fda86490bca98ff21928eec08a&download=Mitigation, Patch, Vendor Advisory
https://talosintelligence.com/vulnerability_reports/TALOS-2021-1301Not Applicable, Third Party Advisory
https://customers.codesys.com/index.php?eID=dumpFile&t=f&f=16805&token=ee583c498941d9fda86490bca98ff21928eec08a&download=Mitigation, Patch, Vendor Advisory
https://talosintelligence.com/vulnerability_reports/TALOS-2021-1301Not Applicable, Third Party Advisory

Timeline

Published: Aug 2, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-21865?

How severe is CVE-2021-21865?

CVE-2021-21865 has a CVSS score of 7.8/10 (HIGH severity). The EPSS model estimates a 1.30% probability of exploitation in the next 30 days.

How do I fix CVE-2021-21865?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-21865?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST