CVE-2025-3699: Mitsubishi Electric Auth Bypass Vulnerability

CVE-2025-3699 Overview

CVE-2025-3699 is a critical Missing Authentication for Critical Function vulnerability (CWE-306) affecting multiple Mitsubishi Electric Corporation air conditioning controller products. This authentication bypass flaw allows remote unauthenticated attackers to gain unauthorized access to critical air conditioning system functions without proper credentials. The vulnerability enables attackers to illegally control HVAC systems, disclose sensitive information, and potentially tamper with firmware using disclosed information.

This vulnerability represents a significant risk to industrial control systems (ICS) and building automation environments, as it provides a network-accessible pathway for complete system compromise without requiring any authentication.

Critical Impact

Remote unauthenticated attackers can bypass authentication to gain full control over air conditioning systems, exfiltrate sensitive operational data, and tamper with device firmware across all affected Mitsubishi Electric controller models.

Affected Products

• Mitsubishi Electric G-50, G-50-W, G-50A (all versions)
• Mitsubishi Electric GB-50, GB-50A, GB-24A, GB-50AD, GB-50ADA-A, GB-50ADA-J (all versions)
• Mitsubishi Electric G-150AD, AG-150A-A, AG-150A-J (all versions)
• Mitsubishi Electric EB-50GU-A, EB-50GU-J (all versions)
• Mitsubishi Electric AE-200J, AE-200A, AE-200E, AE-50J, AE-50A, AE-50E (all versions)
• Mitsubishi Electric EW-50J, EW-50A, EW-50E (all versions)
• Mitsubishi Electric TE-200A, TE-50A, TW-50A (all versions)
• Mitsubishi Electric CMS-RMD-J (all versions)

Discovery Timeline

• 2025-06-26 - CVE-2025-3699 published to NVD
• 2025-12-23 - Last updated in NVD database

Technical Details for CVE-2025-3699

Vulnerability Analysis

This vulnerability stems from a fundamental security design flaw where critical functions within the affected Mitsubishi Electric air conditioning controllers lack proper authentication mechanisms. The Missing Authentication for Critical Function weakness (CWE-306) occurs when a product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.

In the context of building automation and HVAC systems, this vulnerability is particularly concerning because these controllers often manage environmental conditions for critical infrastructure, data centers, healthcare facilities, and industrial environments. An attacker exploiting this vulnerability could manipulate temperature settings, disable climate control systems, or cause equipment damage through improper operation.

The impact extends beyond simple operational disruption. The vulnerability also allows attackers to access sensitive configuration data and operational information stored within the controllers. This disclosed information can then be leveraged to tamper with firmware, potentially establishing persistent backdoor access or causing long-term system compromise.

Root Cause

The root cause of CVE-2025-3699 lies in the absence of authentication requirements for accessing critical management functions within the affected air conditioning controller firmware. The controllers expose administrative and operational interfaces over the network without implementing proper identity verification, allowing any network-accessible attacker to interact with privileged functionality.

This represents a violation of secure design principles where all access to critical functions should require authentication, particularly for network-exposed interfaces in ICS and building automation environments.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no user interaction or prior authentication. An attacker with network access to affected Mitsubishi Electric controllers can directly interact with the vulnerable interfaces to:

1. Bypass authentication - Access administrative functions without credentials
2. Control HVAC systems - Modify temperature settings, schedules, and operational parameters
3. Disclose information - Extract configuration data, operational logs, and system information
4. Tamper with firmware - Leverage disclosed information to modify device firmware

The network-based attack vector with no prerequisites makes this vulnerability particularly dangerous in environments where these controllers are accessible from internal networks or, in worst-case scenarios, exposed to the internet.

Detection Methods for CVE-2025-3699

Indicators of Compromise

• Unexpected configuration changes to HVAC system settings or schedules
• Unauthorized access attempts or connections to air conditioning controller management interfaces
• Anomalous network traffic patterns to/from affected Mitsubishi Electric controllers
• Firmware version changes or unexpected system behavior on controller devices
• Access logs showing connections from unauthorized IP addresses or at unusual times

Detection Strategies

• Implement network monitoring for unauthorized connections to affected controller IP addresses and management ports
• Deploy ICS-aware intrusion detection systems (IDS) to identify anomalous building automation traffic
• Enable and monitor authentication logs on affected devices where available
• Conduct regular configuration audits to detect unauthorized changes to HVAC system parameters
• Use network segmentation monitoring to detect lateral movement attempts toward ICS networks

Monitoring Recommendations

• Establish baseline network behavior for affected Mitsubishi Electric controllers and alert on deviations
• Monitor for firmware integrity changes using file integrity monitoring where supported
• Implement SIEM rules to correlate access patterns across building automation systems
• Set up alerts for access attempts to controller interfaces from untrusted network segments

How to Mitigate CVE-2025-3699

Immediate Actions Required

• Isolate affected Mitsubishi Electric air conditioning controllers from untrusted networks immediately
• Implement strict network segmentation to limit access to affected devices to authorized management stations only
• Deploy firewall rules to restrict access to controller management interfaces
• Review access logs for indicators of prior exploitation or unauthorized access
• Contact Mitsubishi Electric PSIRT for guidance on available mitigations and updates

Patch Information

Organizations should consult the official Mitsubishi Electric PSIRT Security Advisory for the latest patch information and remediation guidance. Additional technical details are available from the CISA ICS Advisory ICSA-25-177-01 and the JVN Vulnerability Report.

Given that all versions of the affected products are vulnerable, organizations should prioritize obtaining vendor guidance on available updates or compensating controls.

Workarounds

• Implement network access control lists (ACLs) to restrict controller access to authorized management stations only
• Deploy VPN or other secure remote access solutions if remote management is required
• Enable logging on all network devices to capture access attempts to affected controllers
• Consider deploying application-aware firewalls or ICS security appliances to inspect and filter traffic to building automation systems
• Implement physical access controls for network segments containing affected devices

# Example network segmentation configuration (Cisco IOS)
# Restrict access to HVAC controller subnet (example: 10.10.100.0/24)
access-list 101 permit ip host 10.10.1.50 10.10.100.0 0.0.0.255
access-list 101 deny ip any 10.10.100.0 0.0.0.255 log
access-list 101 permit ip any any

# Apply to interface facing HVAC network
interface GigabitEthernet0/1
 ip access-group 101 in