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CVE-2026-8066 – Unauthenticated Arbitrary File Write (Path Traversal) – Hitachi Energy RTU500 Series

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Summary

CVE-2026-8066 is a critical relative path traversal vulnerability (CWE-23) in the file upload functionality of Hitachi Energy RTU500 series CMU firmware. An unauthenticated, remote attacker can exploit the flaw to write or overwrite arbitrary files on the device’s file system, potentially leading to unauthorized data modification or disruption of the device’s intended operation. The issue carries a CVSS v3.1 base score of 9.1 (Critical).

Technical details

  • Root cause: The device’s file upload feature fails to properly sanitize or restrict user-supplied file paths, allowing directory traversal sequences to escape the intended upload directory.
  • Trigger conditions: An attacker sends a crafted file upload request containing path traversal sequences to the exposed upload interface; no authentication or user interaction is required.
  • Attack vector: Network-accessible, low attack complexity, no privileges required, no user interaction (AV:N/AC:L/PR:N/UI:N).
  • Impact: Arbitrary file write/overwrite on the device file system, which can result in unauthorized modification of device configuration or data, and disruption of the RTU’s intended operation (integrity and availability impact rated High; no confidentiality impact).

Affected software

  • Hitachi Energy RTU500 series CMU firmware, versions 9.0 through below 12.0

Severity

  • CVSS v3.1 Base Score: 9.1 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade affected RTU500 series CMU firmware to version 12.0 or later, or to a version confirmed by Hitachi Energy to have remediated this vulnerability.
  • If no patch can be applied immediately:
    • Restrict network access to the RTU500 device’s management and file upload interfaces to trusted hosts only, using firewalls and network segmentation.
    • Do not expose RTU500 upload/management interfaces directly to the internet.
    • Monitor device file systems and network traffic for unexpected or unauthorized file upload activity.
    • Follow Hitachi Energy’s general recommended security practices for deploying RTU500 series products in industrial control system environments.

References

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