CVE-2021-26829 OpenPLC ScadaBR Cross-site Scripting Vulnerability
OpenPLC ScadaBR contains a cross-site scripting vulnerability via system_settings.shtm.
From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.
Should You Worry?
- CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 28 Nov 2025.
- Rated Medium severity (CVSS 5.4, scored by CISA).
- It has been in the catalogue for 343 days. Systems still unpatched now have almost certainly been scanned for it.
What It Is
OpenPLC ScadaBR through 0.9.1 on Linux and through 1.12.4 on Windows allows stored XSS via system_settings.shtm.
What To Do Now
- 1
Find it
Search your asset inventory and external attack surface for OpenPLC ScadaBR. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management - 2
Fix 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.
Vulnerability Management - 3
Hunt for compromise
If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.
Incident Response - 4
Prove it is fixed
Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.
Penetration Testing
Vendor Advisories
The Compliance Clock
General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.
Not Sure If You Are Exposed?
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