---
title: "CVE-2021-26829: OpenPLC ScadaBR Cross-site Scripting Vulnerability"
url: https://erroneo.us/security/cve/CVE-2021-26829/
description: "CVE-2021-26829 (OpenPLC ScadaBR): Exploited in the wild (CISA KEV). OpenPLC ScadaBR through 0.9.1 on Linux and through 1.12.4 on Windows allows stored XSS…"
type: vulnerability-record
section: "Security Digest"
date_published: 2021-06-11
date_modified: 2025-12-02
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2021-26829"
kev: true
cvss: 5.4
epss: 0.4805
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2021-26829: OpenPLC ScadaBR Cross-site Scripting Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run OpenPLC ScadaBR. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-11-28, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-12-19 ; treat that as the outer limit, not the target.
- EPSS 48.0% , percentile 99: FIRST’s model estimates a 48.0% chance of exploitation activity in the next 30 days, higher than 99% of all scored CVEs (very high). EPSS is a probability, not a verdict.
- Needs an account (low (any account)). Exposure depends on who can log in.

## What it is

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

## Affected products (CVE record)

- n/a n/a: see advisory

## Severity

- CISA-ADP CVSS 3.1: 5.4 `CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N`

## Exploitation

- CISA KEV: added 2025-11-28; federal due date 2025-12-19. Known ransomware use: Unknown.
- CISA 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.
- CISA SSVC assessment: exploitation active , automatable no , technical impact partial .
- FIRST EPSS (model of 2026-10-21): 48.05% probability of exploitation activity in the next 30 days; percentile 99.

## Sources

- [Listed in CISA KEV notes (github.com)](https://github.com/SCADA-LTS/Scada-LTS/pull/3211)
- [CVE.org record CVE-2021-26829](https://www.cve.org/CVERecord?id=CVE-2021-26829)
- [NVD entry CVE-2021-26829](https://nvd.nist.gov/vuln/detail/CVE-2021-26829)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26829)
- [youtu.be](https://youtu.be/Xh6LPCiLMa8)
- [forum.scadabr.com.br](http://forum.scadabr.com.br/t/report-falhas-de-seguranca-em-versoes-do-scadabr/3615/4)
- [forescout.com](https://www.forescout.com/blog/anatomy-of-a-hacktivist-attack-russian-aligned-group-targets-otics/)

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Source page: https://erroneo.us/security/cve/CVE-2021-26829/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt