Security readout for executives and security teams
Plain-English summary
CVE-2021-21865 affects CODESYS Development System 3.5.16. A maliciously crafted file can trigger unsafe deserialization and potentially run commands on the user's system. The main business risk is compromise of engineering workstations if staff open attacker-supplied files.
Executive priority
Treat this as a high-priority engineering workstation risk. It requires user interaction, but successful exploitation can give broad system impact where CODESYS files are trusted operational inputs.
Technical view
The issue is CWE-502 unsafe deserialization in PackageManagement.plugin ExtensionMethods.Clone(). The CVSS 3.0 score is 8.8 with no privileges required, low attack complexity, and user interaction required. Successful exploitation can affect confidentiality, integrity, and availability.
Likely exposure
Organizations using CODESYS Development System 3.5.16 are the known exposed group, especially engineering teams that receive project, package, or support files from outside trusted channels.
Exploitation context
The provided sources say an attacker can provide a malicious file to trigger command execution. CISA KEV status is false, and the bundle does not cite active exploitation.
Researcher notes
The evidence identifies the vulnerable function and unsafe deserialization class, but this bundle does not include exploit maturity, proof-of-concept status, or precise fixed version details.
Mitigation direction
- Identify installations of CODESYS Development System 3.5.16.
- Check CODESYS vendor guidance for fixed versions or official mitigations.
- Restrict opening CODESYS files from untrusted or unauthenticated sources.
- Use workstation controls to limit impact from unexpected command execution.
- Prioritize remediation on engineering workstations with external file intake.
Validation and detection
- Inventory engineering workstations for CODESYS Development System 3.5.16.
- Confirm whether users receive CODESYS files from vendors, customers, or public channels.
- Review CODESYS advisory details before marking remediation complete.
- Check endpoint telemetry for suspicious activity around CODESYS file handling.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-502: Code execution behavior lookup
Code execution and unsafe deserialization weaknesses often justify reviewing execution behavior and process telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-21865 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.8 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H2.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
8.8HighVector: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://talosintelligence.com/vulnerability_reports/TALOS-2021-1301CVE reference · x_refsource_MISC
- https://customers.codesys.com/index.php?eID=dumpFile&t=f&f=16805&token=ee583c498941d9fda86490bca98ff21928eec08a&download=CVE reference · x_refsource_CONFIRM
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Deserialization of Untrusted Data
Deserialization of Untrusted Data represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.