CODESYS Control RTE (SL): Use of Externally-Controlled Format String
CVE-2026-3509 is a high-severity use of externally-controlled format string vulnerability in CODESYS Control RTE (SL) from Codesys, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 3.5.22.0 as the first without the flaw, so updating CODESYS Control RTE (SL) to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.37% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update CODESYS Control RTE (SL) to 3.5.22.0 or a later version.
- Update CODESYS Control RTE (for Beckhoff CX) SL to 3.5.22.0 or a later version.
- Update CODESYS Control Win (SL) to 3.5.22.0 or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| CODESYS | CODESYS Control RTE (SL) | 3.5.17.0 up to, but not including, 3.5.22.0 | 3.5.22.0 |
| CODESYS | CODESYS Control RTE (for Beckhoff CX) SL | 3.5.17.0 up to, but not including, 3.5.22.0 | 3.5.22.0 |
| CODESYS | CODESYS Control Win (SL) | 3.5.17.0 up to, but not including, 3.5.22.0 | 3.5.22.0 |
| CODESYS | CODESYS Runtime Toolkit | 3.5.17.0 up to, but not including, 3.5.22.0 | 3.5.22.0 |
| CODESYS | CODESYS Control for BeagleBone SL | 4.1.0.0 up to, but not including, 4.21.0.0 | 4.21.0.0 |
| CODESYS | CODESYS Control for emPC-A/iMX6 SL | 4.1.0.0 up to, but not including, 4.21.0.0 | 4.21.0.0 |
| CODESYS | CODESYS Control for IOT2000 SL | 4.1.0.0 up to, but not including, 4.21.0.0 | 4.21.0.0 |
| CODESYS | CODESYS Control for Linux ARM SL | 4.1.0.0 up to, but not including, 4.21.0.0 | 4.21.0.0 |
| CODESYS | CODESYS Control for Linux SL | 4.1.0.0 up to, but not including, 4.21.0.0 | 4.21.0.0 |
| CODESYS | CODESYS Control for PFC100 SL | 4.1.0.0 up to, but not including, 4.21.0.0 | 4.21.0.0 |
| CODESYS | CODESYS Control for PFC200 SL | 4.1.0.0 up to, but not including, 4.21.0.0 | 4.21.0.0 |
| CODESYS | CODESYS Control for PLCnext SL | 4.1.0.0 up to, but not including, 4.21.0.0 | 4.21.0.0 |
| CODESYS | CODESYS Control for Raspberry Pi SL | 4.1.0.0 up to, but not including, 4.21.0.0 | 4.21.0.0 |
| CODESYS | CODESYS Control for WAGO Touch Panels 600 SL | 4.1.0.0 up to, but not including, 4.21.0.0 | 4.21.0.0 |
| CODESYS | CODESYS Virtual Control SL | 4.1.0.0 up to, but not including, 4.21.0.0 | 4.21.0.0 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by CNA (cert.vde.com).
Official description
An unauthenticated remote attacker may be able to control the format string of messages processed by the Audit Log of the CODESYS Control runtime system, potentially resulting in a denial‑of‑service (DoS) condition.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use of Externally-Controlled Format String
The product uses a function that accepts a format string as an argument, but the format string originates from an external source.
How developers prevent this class of flaw
- Choose a language that is not subject to this flaw.
- Ensure that all format string functions are passed a static string which cannot be controlled by the user, and that the proper number of arguments are always sent to that function as well. If at all possible, use functions that do not support the %n operator in format strings.
- Run compilers and linkers with high warning levels, since they may detect incorrect usage.
More Use of Externally-Controlled Format String vulnerabilities (CWE-134)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Other references
Other vulnerabilities in CODESYS Control RTE (SL)
- 7.5 High severity
- 8.1 High severity
- 8.8 High severity
- 7.5 High severity
- 7.5 High severity
- 8.8 High severity
Recent Use of Externally-Controlled Format String vulnerabilities
- 9.1 Critical severity
- 7.2 High severity
- 8.1 High severity
- 7.2 High severity
- 7.5 High severity
- 9.8 Critical severity
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