CVE-2026-35227Network attack vector

Unauthenticated connection exhaustion via handling race

Published May 12, 2026 · Updated May 12, 2026

Resource exhaustion in the Modbus TCP Server stack in CODESYS Modbus before 4.6.0.0 allows remote attackers to block new connections. A race in connection handling leaves connection resources allocated until the configured maximum is exhausted, while existing connections continue operating. The attack requires no authentication but only affects projects with a configured Modbus TCP server, and successful exploitation interrupts new client access without crashing the runtime.

CVSS severity8.2
High
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in the Modbus TCP Server stack in CODESYS Modbus before 4.6.0.0 allows remote attackers to block new connections. A race in connection handling leaves connection resources allocated until the configured maximum is exhausted, while existing connections continue operating. The attack requires no authentication but only affects projects with a configured Modbus TCP server, and successful exploitation interrupts new client access without crashing the runtime.

The record

CVE
CVE-2026-35227
Published
May 12, 2026
Updated
May 12, 2026
Vendor
CODESYS GmbH
Product
CODESYS Modbus
Classifications
CWE-772, T0814
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 12, 2026CVE publishedPublication date reported by the CVE source.
  2. May 12, 2026Record 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=1.0.0.0 <4.6.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

CODESYS GmbH · CODESYS Modbusversion=1.0.0.0 <4.6.0.0

Published CVSS scores

8.2CERT VDECVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
5.9CODESYSCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-772Missing Release of Resource after Effective Lifetime
T0814Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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