CVE-2021-26829
OpenPLC ScadaBR through 0.9.1 on Linux and through 1.12.4 on Windows allows stored XSS via system_settings.shtm.
do firstApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Can a WAF block it? Yes. The vulnerability involves stored cross-site scripting via a web interface page, meaning malicious input is sent in an HTTP request and stored. A WAF can partly detect such attacks by matching typical XSS payload patterns in the parameters of the system_settings.shtm page, but some payloads may resemble normal input. A custom WAF rule can filter stored XSS payload in system_settings.shtm parameter, but attackers can vary the request. No tracked WAF vendor has published a rule for this CVE yet.
What a custom rule would match: stored XSS payload in system_settings.shtm parameter
Also consider: patch · custom WAF rule · CSP · output encoding
Based on an AI reading of the CVE description, and no vendor rule found yet. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.
Is CVE-2021-26829 being exploited?
Yes. CVE-2021-26829 appears in CISA's Known Exploited Vulnerabilities catalog, which means exploitation in the wild has been confirmed and reported. Treat it as active rather than theoretical, and patch it ahead of higher-scoring vulnerabilities that carry no exploitation evidence.
How severe is CVE-2021-26829?
CVE-2021-26829 is rated Medium with a CVSS score of 5.4. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2021-26829?
Yes. A fix has been recorded for CVE-2021-26829. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2021-26829 affect?
CVE-2021-26829 affects scadabr:scadabr. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
cisa ssvc
- exploitation
- active
- automatable
- no
- technical impact
- partial
Assessed by CISA 1 Dec 2025 (SSVC 2.0.3).
timeline
- 11 Jun 2021Published
- 28 Nov 2025Added to CISA KEV (exploited in the wild) · 1,630 days (about 4 years) later
- 1 Dec 2025CISA SSVC assessment: exploitation active · 3 days later
- 2 Dec 2025CVE record last updated · 1 day later
- 19 Dec 2025CISA remediation due date (US federal agencies) · 17 days later
- 2 Nov 2026Analysed by vulneraibility.com · 319 days (about 11 months) later
- Advisoryforescout.com /blog/anatomy-of-a-hacktivist-attack-russian-aligned-group-targets-otics/
- Linkyoutu.be /Xh6LPCiLMa8
- Linkforum.scadabr.com.br /t/report-falhas-de-seguranca-em-versoes-do-scadabr/3615/4
- Linkcisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26829
sources
- CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
- NVD: CVSS and CPE data
- CISA KEV catalog: exploitation, date added, due date
- CISA Vulnrichment (ADP): SSVC decision points
- FIRST EPSS: exploit probability and percentile
- Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.