How severe is CVE-2021-26829?

CVE-2021-26829 has a CVSS score of 5.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-26829?

Affected package information for CVE-2021-26829 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2021-26829?

No fixed version has been published for CVE-2021-26829 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2021-26829 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-26829, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-26829?

CVE-2021-26829 has an EPSS (Exploit Prediction Scoring System) score of 7.6%, placing it in the 92th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

Is CVE-2021-26829 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-26829 (OpenPLC ScadaBR Cross-site Scripting Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2025-11-28. CISA required all US federal civilian agencies to remediate this vulnerability by 2025-12-19. The required action was: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2021-26829?

CVE-2021-26829 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Which products and versions are affected by CVE-2021-26829?

CVE-2021-26829 affects scadabr scadabr. Check the affected-products list on this page against your deployed version to confirm exposure.

When was CVE-2021-26829 published, and has it been updated?

CVE-2021-26829 was published on June 11, 2021 and was last updated on December 1, 2025. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2025-11-28 — agencies required to remediate by 2025-12-19

CVE-2021-26829

MEDIUM

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

Published

Jun 11, 2021

Updated

Dec 1, 2025

Affected

0 pkgs

Patched

None yet

Exploits

1 known

EPSS Exploitation Probability

via FIRST.org ↗

7.6%probability of exploitation in next 30 days

Lower Risk92th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Description

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

Affected Products

1 product · 2 configurations

Application

scadabrscadabr

≤ 1.12.4

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

OpenPLC ScadaBR through 0.9.1 on Linux and through 1.12.4 on Windows all…

youtu.beNVDJun 2021

Frequently Asked Questions

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

O3 Security · Impact-Aware SCA

Is CVE-2021-26829 in your stack?

O3 detects CVE-2021-26829 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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