CVE-2025-53699 in iSTAR Ultra
Summary
by MITRE • 11/14/2026
Missing protection mechanism for alternate hardware interface vulnerability in Johnson Controls iSTAR Ultra, Johnson Controls iSTAR Ultra SE, Johnson Controls iSTAR Ultra G2, Johnson Controls iSTAR Ultra G2 SE, and Johnson Controls iSTAR Edge G2 allows CAPEC‑554: Functionality Bypass.
This issue affects iSTAR Ultra: before 6.9.2.CU02; iSTAR Ultra SE: before 6.9.2.CU02; iSTAR Ultra G2: before 6.9.2.CU02; iSTAR Ultra G2 SE: before 6.9.2.CU02; iSTAR Edge G2: before 6.9.2.CU02.
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Analysis
by VulDB Data Team • 11/14/2026
The vulnerability identified in Johnson Controls iSTAR Ultra, iSTAR Ultra SE, iSTAR Ultra G2, iSTAR Ultra G2 SE, and iSTAR Edge G2 firmware versions prior to 6.9.2.CU02 represents a critical failure in access control mechanisms related to alternate hardware interfaces. This flaw aligns with CAPEC-554, which describes the bypass of intended functionality through unauthorized interaction with system components. In physical security systems like these fire alarm and building automation controllers, multiple communication pathways are often implemented for redundancy, maintenance, or diagnostic purposes. These include serial ports such as RS-232 or RS-485, USB interfaces, JTAG debug headers, or other low-level hardware connections that may not be fully integrated into the primary software-based authentication framework. When these alternate interfaces lack adequate protection mechanisms, they effectively create an unauthenticated backdoor into the system's operating environment and configuration storage.
From a technical perspective, this vulnerability stems from the absence of strict access controls on non-standard or secondary input/output ports. While the main user interface may require robust password authentication to modify critical settings such as zone configurations, alarm priorities, or network parameters, these alternate hardware interfaces often operate at a lower level within the system architecture. Attackers with physical proximity to the device can exploit this discrepancy by connecting directly to these unprotected ports using standard serial-to-USB adapters or specialized debugging tools. This allows them to bypass the application-layer security controls entirely and interact directly with the firmware or operating system, potentially gaining root-level access without valid credentials. The flaw is particularly dangerous in environments where physical security might be perceived as sufficient but lacks rigorous port management policies.
The operational impact of this vulnerability is severe for organizations relying on these systems for life safety and property protection. An attacker exploiting CAPEC-554 can disable alarm notifications, silence fire alarms during an emergency, or manipulate sensor inputs to create false positives that desensitize security personnel. Furthermore, the ability to modify system configurations without authorization compromises the integrity of the entire building automation network. If these controllers are part of a larger IP-based monitoring architecture, compromising one unit could serve as a foothold for lateral movement within the corporate or industrial control network. The lack of audit trails on these alternate interfaces also means that such intrusions may go undetected by standard security information and event management systems until significant damage has occurred.
Mitigation strategies must address both technical controls and physical security protocols. Johnson Controls released version 6.9.2.CU02 to patch this vulnerability, so immediate firmware updates are the primary remediation step for all affected devices. Beyond software updates, organizations should implement strict physical access controls to prevent unauthorized individuals from reaching these alternate hardware interfaces. This includes securing server rooms and equipment closets with multi-factor authentication locks or biometric scanners. Additionally, security administrators should disable any unused serial or debug ports through configuration settings if the firmware supports such isolation features. Regular vulnerability assessments that include physical penetration testing are recommended to identify similar gaps in other connected devices within the infrastructure. Aligning these practices with NIST SP 800-53 controls for access control and system integrity will help ensure a defense-in-depth posture against hardware-level bypass attacks.