RTU500 is a critical OT device in energy/utility infrastructure; unauthenticated arbitrary file overwrite can disrupt operations, safety, or cause widespread outage, so broad alerting is warranted.
CVE-2026-8066
Unauthenticated directory traversal in Hitachi RTU500 allows arbitrary file overwrite.
Is CVE-2026-8066 being exploited?
Not confirmed. CVE-2026-8066 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked.
How severe is CVE-2026-8066?
CVE-2026-8066 is rated Critical with a CVSS score of 9.1. 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-2026-8066?
Not known from our data. No patch reference has been recorded for CVE-2026-8066, which is not the same as no patch existing — a fix may have shipped without a tagged reference, or after this record was written. The vendor advisory is the only authority on whether a fix exists, and mitigations may be available regardless.
What does CVE-2026-8066 affect?
CVE-2026-8066 affects Hitachi Energy RTU500 (end-of-life). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-8066?
Isolate affected RTUs, disable file uploads, apply vendor mitigations, and replace EOL units.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Unauthenticated attacker can traverse upload paths to write/overwrite files, enabling config tampering, firmware compromise, denial of service, or persistent control of the RTU.
Immediate action required
- affected>= 9.0 and < 12.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.