Actively exploited vulnerability

OpenPLC ScadaBR: cross-site scripting flaw under attack

CVE-2021-26829 · OpenPLC ScadaBR Cross-site Scripting Vulnerability

Business software5.4 medium

What is affected

OpenPLC ScadaBR is mostly run by companies, schools and public bodies, not on home computers. You are unlikely to have it yourself, but organisations that hold your data may. Breaches that start with flaws like this one are how personal data ends up leaked.

OpenPLC ScadaBR contains a cross-site scripting vulnerability via system_settings.shtm.

CISA's description

What an attacker can do

This is a cross-site scripting flaw. It lets an attacker plant a script that runs in the browser of anyone who opens the affected page, which lets them steal that person's session or act on their behalf.

How it is reached
Over the internet or network
Access the attacker needs
A basic user account
Does the victim have to do something?
Yes, the victim must open or click something

What to do

  1. At home: nothing to install. Keep your own devices updated and use a different password for every service, so that a breach at one organisation does not open your other accounts.
  2. If you administer OpenPLC ScadaBR at work: apply the vendor's fix or mitigation now and review logs for signs of compromise, because the flaw was being exploited before it was listed.
  3. If the product is past its support date and no fix exists, take it off the internet or retire it.

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Action required by CISA for US federal agencies

Vendor advisories and fixes

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on November 28, 2025, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by December 19, 2025, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 48% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99% of all scored vulnerabilities.

Its CVSS severity score is 5.4 out of 10 (medium), as recorded in the US National Vulnerability Database.

Technical description

OpenPLC ScadaBR through 0.9.1 on Linux and through 1.12.4 on Windows allows stored XSS via system_settings.shtm.

NIST National Vulnerability Database
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