CVE-2021-26828

OpenPLC ScadaBR exploited vulnerability, confirmed exploited in the wild.

OpenPLC ScadaBR contains an unrestricted upload of file with dangerous type vulnerability that allows remote authenticated users to upload and execute arbitrary JSP files via view_edit.shtm.

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39%chance of exploitation in the next 30 days (EPSS), 98th percentile

3 Decadded to CISA's Known Exploited Vulnerabilities list, 2025

24 Decfederal remediation deadline, already passed

Passedpast the deadline: patch now

CISA's name for it	OpenPLC ScadaBR Unrestricted Upload of File with Dangerous Type Vulnerability
Vendor and product	OpenPLC · ScadaBR
Type	exploited vulnerability · CWE-434
Exploited	Confirmed by CISA listed 3 December 2025
Likelihood	one of the most likely to be exploited of every vulnerability tracked
Deadline	24 December 2025 · already passed
Used in ransomware	Not reported
Advisories	github.com ↗ · nvd.nist.gov ↗

What to do

Three steps, in this order

Step 1

Apply the vendor's fix or mitigation; CISA lists only vulnerabilities seen exploited.

Step 2

If you cannot patch now, restrict network access to the affected product.

Step 3

Check for signs of compromise since the date it was added to the list.

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

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Questions

CVE-2021-26828 in short

Is CVE-2021-26828 being exploited?

Yes. CISA added CVE-2021-26828 to its Known Exploited Vulnerabilities catalogue on 3 December 2025, which it does only on evidence of exploitation in the wild.

What is the CISA deadline for CVE-2021-26828?

US federal agencies must remediate it by 24 December 2025. Everyone else should treat that date as the latest safe point to patch an internet-facing system.

How likely is CVE-2021-26828 to be exploited in the next 30 days?

FIRST's Exploit Prediction Scoring System gives it 39%, the 98th percentile of every CVE it scores.

How do I fix CVE-2021-26828?

Apply the vendor's fix or mitigation; CISA lists only vulnerabilities seen exploited. If you cannot patch now, restrict network access to the affected product. Check for signs of compromise since the date it was added to the list.

Same vendor

Other OpenPLC vulnerabilities being exploited

CVE	Product	Type	Listed
CVE-2021-26829	ScadaBR	cross-site scripting	28 November 2025

Sources: CISA Known Exploited Vulnerabilities catalogue (released 10 November 2026) and FIRST EPSS. Page compiled automatically by SAK T.L.M, the threat-intelligence tool of SAK T.E.C, on 13 November 2026.