CVE-2021-21865Network attack vector

Arbitrary code execution via unsafe Package Designer deserialization

Published Aug 2, 2021 · Updated Aug 3, 2024

Unsafe deserialization in CODESYS Development System V3 before 3.5.17.10 allows attackers to execute code through a crafted project file. PackageManagement.plugin's ExtensionMethods.Clone() passes Package Designer tree data to BinaryFormatter.Deserialize without validating serialized types. Execution requires a local user to open the malicious project and invoke copy or paste, and the payload runs in that user's context.

CVSS severity8.8
High
EPSS probability1.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unsafe deserialization in CODESYS Development System V3 before 3.5.17.10 allows attackers to execute code through a crafted project file. PackageManagement.plugin's ExtensionMethods.Clone() passes Package Designer tree data to BinaryFormatter.Deserialize without validating serialized types. Execution requires a local user to open the malicious project and invoke copy or paste, and the payload runs in that user's context.

The record

CVE
CVE-2021-21865
Published
Aug 2, 2021
Updated
Aug 3, 2024
Vendor
CODESYS GmbH
Product
CODESYS Development System V3
Classifications
CWE-502, T1203, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 2, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=CODESYS GmbH CODESYS Development System 3.5.16

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

CODESYS GmbH · CODESYS Development System V3version=CODESYS GmbH CODESYS Development System 3.5.16

Published CVSS scores

8.8CODESYS GmbHCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-502Deserialization of Untrusted Data
T1203Exploitation for Client Execution
T1204.002Malicious File

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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