CVE-2021-34540: Advantech WebAccess 8.4.2 and 8.4.4 allows XSS via the username column of the bwRoot.asp page of WADashboard.

This month

MEDIUM 6.1DOWNGRADE

CVE-2021-34540 is a medium-severity flaw (CVSS 6.1) affecting webaccess. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Advantech WebAccess 8.4.2 and 8.4.4 allows XSS via the username column of the bwRoot.asp page of WADashboard.

Why this priority

Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.9% (top 41%)
CISA exploited list	No
Weakness	CWE-79
Published	2021-06-11
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: advantech

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

Am I affected?

Timeline

2021-06-11 12:15 UTCPublished CVE record published
2026-06-17 03:56 UTCUpdated Record last modified

advantech webaccess DOWNGRADE

Affected: 8.4.2 · 8.4.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.4.2

1. Check installed version

apt-cache policy webaccess || rpm -q webaccess || webaccess --version

2. No fixed release: DOWNGRADE to a release before 8.4.2 (Debian / Ubuntu)

apt-cache madison webaccess sudo apt install webaccess=<VERSION_BEFORE_8.4.2> sudo apt-mark hold webaccess

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

dnf --showduplicates list webaccess sudo dnf downgrade webaccess-<VERSION_BEFORE_8.4.2> sudo dnf versionlock add webaccess

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-2021-34540?

webaccess: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-34540 being exploited?

CVE-2021-34540 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-2021-34540 affect?

CVE-2021-34540 affects webaccess. Severity is medium (CVSS 6.1). Advantech WebAccess 8.4.2 and 8.4.4 allows XSS via the username column of the bwRoot.asp page of WADashboard.

How urgent is CVE-2021-34540?

Priority 41/100. Public exploit reference

Software pages

Advantech vulnerabilities

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References

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