CVE-2021-43931: The authentication algorithm of the WebHMI portal is sound, but the implemented mechanism can be bypassed as t

Q: How do I fix CVE-2021-43931?

webhmi firmware: upgrade to 4.1. Exact commands for each OS are on this page.

Q: Is CVE-2021-43931 being exploited?

CVE-2021-43931 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-43931 affect?

CVE-2021-43931 affects webhmi firmware. Severity is critical (CVSS 9.8). The authentication algorithm of the WebHMI portal is sound, but the implemented mechanism can be bypassed as the result of a separate weakness that is primary to the authentication error.

Q: How urgent is CVE-2021-43931?

Priority 58/100. Critical severity; Remotely exploitable, no login, no user action

This month

CRITICAL 9.8REMOTEUPGRADE

CVE-2021-43931 is a critical-severity flaw (CVSS 9.8) affecting webhmi firmware. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The authentication algorithm of the WebHMI portal is sound, but the implemented mechanism can be bypassed as the result of a separate weakness that is primary to the authentication error.

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	1.5% (top 26%)
CISA exploited list	No
Weakness	CWE-287
Published	2021-12-06
Last modified	2026-06-17

Publisher (CNA): ICS-CERT · Vendor: webhmi

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

Am I affected?

Timeline

2021-12-06 18:15 UTCPublished CVE record published
2026-06-17 04:11 UTCUpdated Record last modified

webhmi webhmi firmware UPGRADE

Affected: < 4.1

Fixed in: 4.1

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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-2021-43931?

webhmi firmware: upgrade to 4.1. Exact commands for each OS are on this page.

Is CVE-2021-43931 being exploited?

CVE-2021-43931 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-2021-43931 affect?

CVE-2021-43931 affects webhmi firmware. Severity is critical (CVSS 9.8). The authentication algorithm of the WebHMI portal is sound, but the implemented mechanism can be bypassed as the result of a separate weakness that is primary to the authentication error.

How urgent is CVE-2021-43931?

Priority 58/100. Critical severity; Remotely exploitable, no login, no user action

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References

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