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CVE-2026-35227
An unauthenticated remote attacker may exhaust all available TCP connections in the CODESYS Modbus TCP Server stack if a race condition in connection handling is successfully exploited, preventing legitimate clients from establishing new connections.
This record: live connection— last retrieved: 7 November 2026 at 01:34.
Vendor
Published
12 May 2026
Last modified
26 October 2026
Taken directly from NVD, CISA or the vendor — sometimes in English, unchanged from the source.
An unauthenticated remote attacker may exhaust all available TCP connections in the CODESYS Modbus TCP Server stack if a race condition in connection handling is successfully exploited, preventing legitimate clients from establishing new connections.
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack vector
NETWORK
Privileges required
NONE
User interaction
NONE
Confidentiality
None
Integrity
None
Availability
High
Probability of exploitation within 30 days
0.4%
Percentile
29e
Source: FIRST.org, updated on 6 November 2026.
Update the following product to version 4.6.0.0. * CODESYS Modbus To make the fix effective for existing CODESYS projects, you must additionally update the local Modbus TCP Server in the device tree to the latest version and perform a download of the CODESYS application to the PLC. The CODESYS Development System and the products available as CODESYS add-ons can be downloaded and installed directly with the CODESYS Installer or be downloaded from the CODESYS Store. Alternatively, as well as for all other products, you will find further information on obtaining the software update in the CODESYS Update area https://www.codesys.com/download/.
Our own interpretation and context for the source data above.
IACS Radar assessment
Our own interpretation and context for this vulnerability — not an official source.
IACS Radar priority score
Based on CVSS 8.2, EPSS 0.4%, industrial relevance 45/100; raised due to relevance to internet exposure.
Combines CVSS, EPSS, KEV status, industrial relevance and exposure relevance — a complement to, not a replacement for, the individual scores below and above.
Conditions for exploitation
Operational impact & energy relevance
Possible loss of visibility of or control over the process upon successful exploitation.
No strong energy-sector-specific signals recognised; general OT/ICS relevance.
This product uses protocols that are relevant to internet exposure analysis. An internet-reachable service is not automatically vulnerable.
Recommended defensive measures
Industrial relevance score
Classification is provisional; manual verification by an OT security analyst is recommended.
Classified by IACS Radar-analysepijplijn (geautomatiseerd) on 7 November 2026.
IEC 62443 mapping
Automatic IACS Radar assessment based on the reported CWE weakness classification; not an official certification statement.