CVE-2021-26829 OpenPLC ScadaBR: web page flaw
In plain words: A web app can be made to act on someone's behalf or reach places it should not. Stolen sessions, actions taken as the victim, or access to internal systems.
Confirmed exploited by CISA on · US federal patch deadline Dec 19, 2025
What to do
- Install OpenPLC's security update for ScadaBR. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Keep a list of every internet-facing server you run so nothing is forgotten.
- Patch anything in this catalog first, ahead of normal patch cycles.
- Put admin and file-transfer apps behind a VPN or single sign-on instead of the open internet.
Who is affected
Work IT. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.
What's at risk: Mass data theft and ransomware: a single flaw in a file-transfer or email server has exposed thousands of organisations at once.
The details
- Official name
- OpenPLC ScadaBR Cross-site Scripting Vulnerability
- Product
- OpenPLC ScadaBR
- CISA description
- OpenPLC ScadaBR contains a cross-site scripting vulnerability via system_settings.shtm.
- Type of flaw
- Web page flaw (CWE-79)
- Confirmed exploited
- Nov 28, 2025
- US federal patch deadline
- Dec 19, 2025
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Answering about CVE-2021-26829 ·
Questions about CVE-2021-26829
Is CVE-2021-26829 being exploited?
Yes. CISA added CVE-2021-26829 to its Known Exploited Vulnerabilities catalog on Nov 28, 2025, which means there is reliable evidence of real-world attacks.
How do I fix CVE-2021-26829?
Install OpenPLC's security update for ScadaBR. If no update exists, follow the vendor's workaround or stop using the product until one ships. Keep a list of every internet-facing server you run so nothing is forgotten.
Am I affected by CVE-2021-26829?
Only if you use OpenPLC ScadaBR. Aimed mostly at company systems — you are affected through the companies you use, not your own phone.