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

> Attackers can inject malicious scripts into the system settings page, potentially compromising user sessions and executing code in the victim's browser.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Yes, since 28 Nov 2025 (CISA KEV)
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 11 Jun 2021
- **Updated:** 2 Dec 2025
- **Also known as:** GHSA-6pvv-xrf9-29m6

## What is CVE-2021-26829?

CVE-2021-26829 is a medium-severity cross-site scripting vulnerability in n/a, published on 11 Jun 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

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

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2021-26829?

It affects 1 product.


Products: Scadabr Scadabr.

## How do I fix CVE-2021-26829?

No fix has been published for CVE-2021-26829 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 19 Dec 2025.

## Is CVE-2021-26829 being exploited?

Yes. Attackers have exploited CVE-2021-26829 in the wild since at least 28 Nov 2025.

## Other vulnerabilities in n/a

- [CVE-2021-26828](https://insights.sbomify.com/CVE-2021-26828/): OpenPLC ScadaBR Unrestricted Upload of File with Dangerous Type (high 8.8, exploited in the wild)
- [CVE-2026-9645](https://insights.sbomify.com/CVE-2026-9645/): ScadaBR Authenticated Remote Code Execution (critical 9.9)
- [CVE-2026-8602](https://insights.sbomify.com/CVE-2026-8602/): Missing authentication for critical function in ScadaBR (high 8.8)
- [CVE-2026-8603](https://insights.sbomify.com/CVE-2026-8603/): Improper neutralization of special elements used in an OS command ('OS command injection') in ScadaBR (high 8.7)
- [CVE-2026-8604](https://insights.sbomify.com/CVE-2026-8604/): Cross-Site request forgery (CSRF) in ScadaBR (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-26829 and fix it if it is affected.

What it is: CVE-2021-26829 is a medium-severity cross-site scripting vulnerability in n/a, published on 11 Jun 2021. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Exploitation: Yes. Attackers have exploited CVE-2021-26829 in the wild since at least 28 Nov 2025.

Affected product: n/a. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-26829/ (Markdown: https://insights.sbomify.com/CVE-2021-26829/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-26829
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-26829
- OSV: https://osv.dev/vulnerability/CVE-2021-26829

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-26829/
Summaries are generated and may contain mistakes; the official description above is the record.