Threats / OpenPLC / CVE-2021-26829
CVE-2021-26829
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
OpenPLC ScadaBR vulnerability
OpenPLC ScadaBR contains a cross-site scripting vulnerability in system_settings.shtm that allows injection of malicious scripts.
Verdict
Today item — known-exploited.
A reflected or stored XSS flaw in the system settings interface enables attackers to execute arbitrary JavaScript in administrator browsers, potentially leading to credential theft, session hijacking, or unauthorized configuration changes.
CISA KEV Yes · 2025-11-284EPSS 0.4805 (verify live)5CVSS 5.4 (CISA)3CISA SSVC Exploitation: active · Automatable: no · Impact: partial3
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
6 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2025-11-28).
Probability (EPSS)
EPSS 0.4805 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 5.4 (CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N) · Affected: OpenPLC, ScadaBR. Confirm exact fixed builds in the vendor advisory.CVSS — CISA-assigned via the ADP container (CVE.org), version 3.1; the CNA left no metrics, so CISA's own score is used ahead of NVD.
Weakness (CWE)
Mapped to CWE-79 Cross-site Scripting (XSS) — weakness family: Web / client.CWE assignment from the public NVD record (may be stale); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: no · Technical Impact: partialCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 1631 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious URL or inject payload into system_settings.shtm parameters to execute JavaScript in the victim's browser.
Business
Administrative users are tricked into visiting attacker-controlled links or viewing compromised settings pages, exposing their session tokens and credentials.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I steal the administrator's session cookie or authentication token via the injected script.
Business
Attackers gain unauthorized access to the SCADA system with full administrative privileges, bypassing normal access controls.
3
Lateral reach — past segmentation narrative 3
Attacker
I modify system settings, disable security features, or inject persistent malicious code into the application.
Business
Critical infrastructure monitoring and control functions are compromised, enabling further lateral movement or operational disruption.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05