CVE Intelligence
CISA KEV Medium Cross-site scripting exploit reference

CVE-2021-26829 — OpenPLC ScadaBR Cross-site Scripting Vulnerability

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 Oct 13, 2026 · Sources: CISA Known Exploited Vulnerabilities, CVE Program (cve.org) e CISA ADP, NIST National Vulnerability Database, GitHub Security Advisories · CNA: mitre

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

CISA KEV · Nov 28, 2025
How the score was calculated
  • Confirmed exploitation (CISA KEV)+35
  • EPSS 48.1% (30-day exploitation probability)+15
  • Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Confirmed
CISA KEV, listed Nov 28, 2025
EPSS FIRST
48.05%
ahead of 99% of scored CVEs · Oct 14, 2026
Affects
Scadabr
Scadabr
CVSS base
5.4
Medium · 4 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
Active
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

CISA required action CISA

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

US federal deadline: Dec 19, 2025 — passed 300 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Scadabr Scadabr).
  2. Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
  3. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  4. Exploitation requires user interaction: tighten email/web filtering and warn affected users.
  5. EPSS ahead of 99% of scored CVEs: prioritize it in the patch queue.
  6. Search available logs for exploit probes matching the vulnerability class (cross-site scripting), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Scadabr Scadabr ≤ 0.9.1≤ 1.12.4 Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
5.4 CVSS 3.1 Medium 2.3 2.7 nvd@nist.gov via NIST National Vulnerability Database
5.4 CVSS 3.1 Medium 2.3 2.7 134c704f-9b21-4f2e-91b3-4a467353bcc0 via NIST National Vulnerability Database
5.4 CVSS 3.1 Medium — — GitHub, Inc. via GitHub Security Advisories
5.4 CVSS 3.1 Medium — — CISA-ADP via CVE Program (cve.org) e CISA ADP
3.5 CVSS 2.0 Low 6.8 2.9 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-79 · Cross-site Scripting (XSS)

Other CVEs with this weakness →

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

Listed
Nov 28, 2025
Federal deadline
Dec 19, 2025
passed 300 day(s) ago
Ransomware use
Unknown

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

EPSS over time FIRST

Oct 12, 2026 → Oct 14, 2026 · 3 reading(s) · max 48.05%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Monitor CSP violation reports and script payloads in reflected parameters.
  • Hunt retroactively in logs from before Nov 28, 2025 (KEV listing): exploitation may have started earlier.
web/proxy/WAF logsnetwork IDS/IPSapplication logs

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · scadabr/scadabr
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · Published → Analyzed
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record published
    Oct 13, 2026
  • CVSS changed · 5.4
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Source status changed · → Published
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Added to CISA KEV (detected)
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • Record created in this database
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • 2025
  • Added to CISA KEV catalog
    Nov 27, 2025 · CISA
  • 2021
  • CVE published
    Jun 11, 2021 · mitre

Source activity

Repeated readings are counted rather than listed.

  • 3× References added · Oct 13, 2026 – Oct 13, 2026
  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

7 on the record

Elsewhere on this site

Scadabr
every CVE for this vendor
2025-11
what else CISA listed that month
Cross-site scripting
same class
CWE-79
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-9646 ScadaBR Unauthenticated Reflected Cross-Site Scripting May 28, 2026
  • CVE-2026-9645 ScadaBR Authenticated Remote Code Execution May 28, 2026
  • CVE-2026-8604 Cross-Site request forgery (CSRF) in ScadaBR May 19, 2026
  • CVE-2026-8605 Use of Hard-coded Credentials in ScadaBR May 19, 2026
  • CVE-2026-8602 Missing authentication for critical function in ScadaBR May 19, 2026
  • CVE-2026-8603 Improper neutralization of special elements used in an OS command ('OS command injection') in ScadaBR May 19, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No fixed version, patch or mitigation documented.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-26829 is "OpenPLC ScadaBR Cross-site Scripting Vulnerability", rated Medium. It affects Scadabr (Scadabr); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 5.4 describes technical severity. EPSS 48.05% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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