Security readout for executives and security teams
Plain-English summary
CVE-2021-21864 affects CODESYS Development System 3.5.16 and 3.5.17. A malicious file can abuse unsafe deserialization to run commands on the user’s workstation. The business risk is compromise of engineering systems if staff open untrusted files.
Executive priority
Treat as high priority for engineering environments. It is not described as remotely exploitable, but user-assisted file attacks can compromise sensitive automation workstations.
Technical view
The issue is CWE-502 unsafe deserialization in ComponentModel ComponentManager.StartupCultureSettings. CVSS is 7.8, with local attack vector, no privileges required, user interaction required, and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is likely limited to organizations running CODESYS Development System 3.5.16 or 3.5.17 on engineering workstations that may open externally supplied files.
Exploitation context
The attacker must provide a specially crafted file and get a user to open it. The bundle does not show CISA KEV listing or active exploitation evidence.
Researcher notes
Evidence supports arbitrary command execution through unsafe deserialization in a specific CODESYS Development System component. The provided data does not establish affected runtime devices, public exploitation, or a named fixed version.
Mitigation direction
- Identify and upgrade affected CODESYS Development System 3.5.16 or 3.5.17 per CODESYS guidance.
- Block opening untrusted CODESYS files on engineering workstations until remediation is complete.
- Restrict file transfer paths into engineering workstations, including email, web downloads, and removable media.
- Use endpoint controls to monitor unexpected process launches from CODESYS tools.
Validation and detection
- Inventory installed CODESYS Development System versions across engineering workstations.
- Confirm whether versions 3.5.16 or 3.5.17 are present.
- Review CODESYS advisory for fixed versions and vendor-specific remediation instructions.
- Check endpoint telemetry for unusual child processes launched by CODESYS applications.
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-2021-21864 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
- 7.8 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/AV:L/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:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H1.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
7.8HighVector: CVSS:3.0/AV:L/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.