How severe is CVE-2021-21865?

CVE-2021-21865 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-21865 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (67th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-21865?

CVE-2021-21865 primarily affects Codesys Development System. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-21865?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-21865 published?

CVE-2021-21865 was published on 2021-08-02 and last updated on 2026-06-17.

CVE-2021-21865

CVE-2021-21865 is a high-severity vulnerability in Codesys Development System with a CVSS 3.x base score of 7.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-502.

Key facts

Severity: High (CVSS 3.x base score 7.8)
CVSS v2: 6.8
EPSS exploit prediction: 1% (67th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-502
Affected product: Codesys Development System
Published: 2021-08-02
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-21865?: 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.
How severe is CVE-2021-21865?: CVE-2021-21865 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-21865 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (67th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21865?: CVE-2021-21865 primarily affects Codesys Development System. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-21865?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-21865 published?: CVE-2021-21865 was published on 2021-08-02 and last updated on 2026-06-17.

References

Affected products (2)

cpe:2.3:a:codesys:development_system:3.5.16.0:*:*:*:*:*:*:*
cpe:2.3:a:codesys:development_system:3.5.17.0:*:*:*:*:*:*:*

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