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PatchSiren cyber security CVE debrief

CVE-2021-26828 OpenPLC CVE debrief

CVE-2021-26828 is an unrestricted upload of file with dangerous type vulnerability affecting OpenPLC ScadaBR. CISA has added it to the Known Exploited Vulnerabilities catalog, which means defenders should treat it as an urgent remediation item rather than a routine patch. If ScadaBR is exposed or reachable in production, prioritize mitigation immediately and follow CISA guidance if no effective mitigation is available.

Vendor
OpenPLC
Product
ScadaBR
CVSS
Unknown
CISA KEV
Listed
Original CVE published
2025-12-03
Original CVE updated
2025-12-03
Advisory published
2025-12-03
Advisory updated
2025-12-03

Who should care

Organizations running OpenPLC ScadaBR, especially OT/ICS and SCADA teams, security operations, vulnerability management teams, and any administrators responsible for internet-facing or business-critical deployments.

Technical summary

The issue is identified as an unrestricted upload of file with dangerous type in OpenPLC ScadaBR. At a minimum, this class of flaw can allow unauthorized placement of files that should not be accepted by the application, creating a path to broader compromise depending on how the product is deployed. CISA lists the vulnerability in its Known Exploited Vulnerabilities catalog, indicating active defensive urgency.

Defensive priority

High — CISA KEV-listed; remediate immediately and do not defer beyond the KEV due date if the product is in use.

Recommended defensive actions

  • Inventory all OpenPLC ScadaBR deployments and determine whether any instance is externally reachable or production-critical.
  • Apply vendor-recommended mitigations or updates as soon as possible.
  • If effective mitigations are not available, discontinue use of the product per CISA guidance.
  • Restrict access to any upload-related functionality and limit exposure to trusted administrative networks only.
  • Monitor for suspicious file creation, unexpected content in upload directories, and other indicators of unauthorized upload activity.
  • If the product is used in cloud services, follow applicable BOD 22-01 guidance referenced by CISA.

Evidence notes

The vulnerability name, vendor project, and product are taken from the CISA KEV source item and the official KEV catalog entry. The KEV metadata explicitly marks CVE-2021-26828 as known exploited, with dateAdded 2025-12-03 and dueDate 2025-12-24. Official reference links provided in the corpus include the CVE record, NVD detail page, and CISA KEV catalog.

Official resources

Publicly listed by CISA in the Known Exploited Vulnerabilities catalog; this debrief avoids exploit steps and focuses on defensive response.