CVE-2021-26829: OpenPLC ScadaBR exploited

Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.

What it is

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

Description quoted from the CVE record (assigned by mitre, published 2021-06-11).

Weakness: CWE-79 Improper Neutralization of Input During Web Page Generation (‘Cross-site Scripting’)

How it can be exploited

Exploitable over the network with low attack complexity needing low privileges and a user must take an action. Impact: confidentiality low, integrity low, availability none. CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CISA assessment (SSVC): CISA assesses exploitation as active. Automatable: no. Technical impact: partial.

On CISA KEV since: 2025-11-28
US federal deadline: 2025-12-19
Ransomware use: Not known

Public exploit evidence (Exploit Observer)

Also known as: BDU:2025-14902, CNNVD-202106-1193, CNVD-2021-44288, EUVD-2021-13614, GHSA-6pvv-xrf9-29m6

VEDAS cluster: VEDAS:FAUNTINGFLAMINGO

Exploit Observer links 5 pieces of public exploit code or detection modules that name this CVE or one of its aliases.

Exploit code and modules (5)

Code that names this CVE. A repository can be a working exploit, a scanner, a fake or malware; read it before running anything.

Vulnerability databases and vendor advisories (6)

Catalogue entries, not exploit evidence.

Vulnerability database or vendor advisory: https://euvd.enisa.europa.eu/enisa/EUVD-2021-13614
Vulnerability database or vendor advisory: https://github.com/advisories/GHSA-6pvv-xrf9-29m6
Vulnerability database or vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-26829
Vulnerability database or vendor advisory: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26829
Vulnerability database or vendor advisory: https://www.cnnvd.org.cn/home/globalSearch?keyword=CNNVD-202106-1193
Vulnerability database or vendor advisory: https://www.cnvd.org.cn/flaw/show/CNVD-2021-44288

18 more references returned by Exploit Observer did not name this CVE or an alias, so they are left out.

VEDAS data as of 2026-11-01T17:12 UTC; fetched 2026-11-02.

Live scores

EPSS: 0.480
likely to be attacked soon
VEDAS: 0.979
strong exploit evidence
On CISA KEV: Yes, since 2025-11-28
Detection rule: Nuclei · Suricata

EPSS (chance of attack)

VEDAS (exploit evidence)

Thin horizontal line: the “likely” (EPSS 0.10) or “strong” (VEDAS 0.90) threshold. Shaded “no data” areas are periods when cve-scores did not publish. The vertical line is the day CISA added it to its exploited list.

Who is affected

Product	Affected	Not affected
Not stated	version n/a	Not stated

Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.

How to fix it

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.

Vendor guidance:

How to detect it

Nuclei template (active check)

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

Name and description quoted from the template, written by VEDAS.

The template sends 1 request (GET /index.php?q=); it decides using status, word matchers. Severity in the template: medium. Marked as not yet verified against a live vulnerable target.

Run it against a host you own or are authorised to test:

bash

nuclei -u https://your-host -t CVE-2021-26829.yaml

Show the template (38 lines)

yaml

id: CVE-2021-26829

info:
  name: "OpenPLC ScadaBR - Cross-Site Scripting"
  author: vedas-arpsyndicate
  severity: medium
  description: |
    OpenPLC ScadaBR through 0.9.1 on Linux and through 1.12.4 on Windows allows stored XSS via
    system_settings.shtm.
  reference:
    - https://www.exploit.observer/?keyword=CVE-2021-26829&match=exact
    - https://subdomain.center/?engine=ammonites&keyword=openplc&match=exact
  classification:
    cvss-score: 5.4
    cve-id: CVE-2021-26829
    cwe-id: CWE-79
  metadata:
    verified: false
    max-request: 1
  tags: cve,cve2021,openplc,xss

http:
  - method: GET
    path:
      - '{{BaseURL}}/index.php?q="><script>confirm(1kw9dtm5)</script>'
    matchers-condition: and
    matchers:
      - type: word
        part: body
        words:
          - '"><script>confirm(1kw9dtm5)</script>'
      - type: word
        part: header
        words:
          - "text/html"
      - type: status
        status:
          - 200

CVE-2021-26829.yaml on GitHub

Suricata rules (network detection)

1 rule that alert on traffic matching this exploit: VEDAS CVE-2021-26829 OpenPLC ScadaBR - Cross-Site Scripting. Add them to your Suricata rule set and reload.

Show the rules

suricata

alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2021-26829 OpenPLC ScadaBR - Cross-Site Scripting"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"index.php"; nocase; fast_pattern; content:"<script"; nocase; classtype:web-application-attack; reference:cve,CVE-2021-26829; reference:url,https://www.exploit.observer/?keyword=CVE-2021-26829&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=openplc&match=exact; sid:1004633; rev:2;)

CVE-2021-26829.rules on GitHub

References

Other databases

Where this comes from

This advisory is generated automatically by VEDAS from: CVE.org record, CISA KEV, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.