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CVE-2026-8065 – Authentication Bypass Enabling Arbitrary Firmware Upload – Hitachi Energy RTU500 ser

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Summary

CVE-2026-8065 is a critical authentication bypass vulnerability (CVSS 9.1) affecting the firmware update endpoint of Hitachi Energy RTU500 series CMU firmware. An unauthenticated, remote attacker can send a crafted POST request to the update endpoint and upload arbitrary firmware without providing any credentials. Successful exploitation can modify device functionality and compromise the integrity and availability of the remote terminal unit.

Technical details

  • Root cause: The firmware update endpoint on affected RTU500 CMU devices is missing an authentication check (CWE-306, Missing Authentication for Critical Function), allowing unauthenticated requests to reach a function intended for privileged use.
  • Trigger conditions: An attacker crafts a POST request to the firmware update endpoint containing arbitrary firmware content; no valid session, credentials, or prior authentication is required.
  • Attack vector: Network-based (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N).
  • Impact: High impact to integrity and availability of the device (the vulnerability does not affect confidentiality per the CVSS vector). A successful upload of attacker-supplied firmware could alter device behavior, disrupt operation, or render the RTU unavailable — significant given RTU500 units are used for substation automation and remote control in energy/grid environments.
  • Related weakness: Mapped to CAPEC-638 (Altered Component Firmware).

Affected software

  • Hitachi Energy RTU500 series CMU firmware, versions 9.0 up to (but not including) 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, and consult Hitachi Energy’s cybersecurity advisory (document 8DBD000251) for the exact release and update procedure for your device configuration.
  • If patching cannot be performed immediately:
    • Restrict network access to the RTU500 management/firmware-update interface to trusted management networks only, using firewalls, VPNs, or network segmentation.
    • Ensure RTU500 devices are not directly exposed to the public internet.
    • Monitor for unexpected firmware update requests or unplanned firmware changes on affected devices.
    • Follow general ICS network hardening guidance (e.g., isolating OT networks from IT/corporate networks and the internet) until the firmware update is applied.

References

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