CVE-2018-5440: A Stack-based Buffer Overflow issue was discovered in 3S-Smart CODESYS Web Server

This week

CRITICAL 9.8REMOTEUPGRADEDOWNGRADE

CVE-2018-5440 is a critical-severity flaw (CVSS 9.8) affecting codesys runtime system, codesys web server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A Stack-based Buffer Overflow issue was discovered in 3S-Smart CODESYS Web Server. Specifically: all Microsoft Windows (also WinCE) based CODESYS web servers running stand-alone Version 2.3, or as part of the CODESYS runtime system running prior to Version V1.1.9.19. A crafted request may cause a buffer overflow and could therefore execute arbitrary code on the web server or lead to a denial-of-service condition due to a crash in the web server.

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	3.1% (top 12%)
CISA exploited list	No
Weakness	CWE-121, CWE-787
Published	2018-02-15
Last modified	2026-06-17

Publisher (CNA): ICS-CERT · Vendor: 3s-software

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2018-02-15 10:29 UTCPublished CVE record published
2026-06-17 02:00 UTCUpdated Record last modified

3s-software codesys runtime system UPGRADE

Affected: < 1.1.9.19

Fixed in: 1.1.9.19

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy codesys-runtime-system || rpm -q codesys-runtime-system || codesys-runtime-system --version

2. UPGRADE to 1.1.9.19 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade codesys-runtime-system

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade codesys-runtime-system

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3s-software codesys web server DOWNGRADE

Affected: 2.3

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.3

1. Check installed version

apt-cache policy codesys-web-server || rpm -q codesys-web-server || codesys-web-server --version

2. No fixed release: DOWNGRADE to a release before 2.3 (Debian / Ubuntu)

apt-cache madison codesys-web-server sudo apt install codesys-web-server=<VERSION_BEFORE_2.3> sudo apt-mark hold codesys-web-server

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list codesys-web-server sudo dnf downgrade codesys-web-server-<VERSION_BEFORE_2.3> sudo dnf versionlock add codesys-web-server

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2018-5440?

codesys runtime system: upgrade to 1.1.9.19; codesys web server: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2018-5440 being exploited?

CVE-2018-5440 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2018-5440 affect?

CVE-2018-5440 affects codesys runtime system, codesys web server. Severity is critical (CVSS 9.8). A Stack-based Buffer Overflow issue was discovered in 3S-Smart CODESYS Web Server. Specifically: all Microsoft Windows (also WinCE) based CODESYS web servers running stand-alone Version 2.3, or as part of the CODESYS runtime system running

How urgent is CVE-2018-5440?

Priority 61/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

Windows vulnerabilities

References

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