CVE-2025-26386: Johnson Controls ICU Buffer Overflow Flaw

CVE-2025-26386 Overview

CVE-2025-26386 is a stack-based buffer overflow vulnerability affecting Johnson Controls iSTAR Configuration Utility (ICU), a tool used for configuring iSTAR access control systems commonly deployed in physical security environments. The vulnerability exists in ICU version 6.9.7 and prior versions. Successful exploitation of this vulnerability could result in failure within the operating system of the machine hosting the ICU tool, potentially causing denial of service conditions.

Critical Impact

Exploitation of this stack-based buffer overflow can cause operating system failure on hosts running the ICU configuration tool, disrupting physical access control system management and potentially leaving security infrastructure in an unmanaged state.

Affected Products

• Johnson Controls iSTAR Configuration Utility (ICU) version 6.9.7
• Johnson Controls iSTAR Configuration Utility (ICU) versions prior to 6.9.7

Discovery Timeline

• 2026-01-28 - CVE-2025-26386 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2025-26386

Vulnerability Analysis

This vulnerability is classified as CWE-121: Stack-based Buffer Overflow, a memory corruption vulnerability that occurs when a program writes data beyond the boundaries of a fixed-length buffer on the stack. In the context of the iSTAR Configuration Utility, the vulnerability can be triggered over a network connection, though it requires user interaction to exploit successfully.

The attack does not require authentication or special privileges, making it accessible to unauthenticated remote attackers. However, the user interaction requirement indicates that some form of social engineering or manipulation of the user interface may be necessary to trigger the vulnerable code path. The primary impact is on system availability, with the potential for high availability impact and limited integrity impact.

Root Cause

The root cause of CVE-2025-26386 is improper bounds checking when handling input data within the iSTAR Configuration Utility. When processing certain inputs, the application fails to validate the size of data being written to stack-allocated buffers. This allows an attacker to supply oversized input that overwrites adjacent memory on the stack, potentially corrupting return addresses, saved registers, or other critical stack data structures.

Stack-based buffer overflows are particularly dangerous because the stack contains execution control data. When this data is corrupted, it can lead to application crashes, denial of service, or in some cases, arbitrary code execution if the attacker can precisely control the overwritten values.

Attack Vector

The attack vector for this vulnerability is network-based, meaning an attacker can potentially trigger the vulnerability remotely. The exploitation scenario involves the following conditions:

The attacker must be able to communicate with the ICU application over the network and must induce some form of user interaction on the target system. This could involve sending malicious configuration data or crafted network packets that are processed by the ICU tool when a user performs certain actions.

Given the nature of iSTAR access control systems, which are typically used in enterprise physical security deployments, the attack surface may be limited to internal networks or VPN-connected environments. However, any successful exploitation could disrupt the ability to manage and configure physical access control systems, potentially impacting building security operations.

The vulnerability mechanism involves overflowing stack memory when processing input data. Attackers may craft payloads that exceed expected buffer sizes, causing memory corruption. For detailed technical information, refer to the CISA ICS Advisory ICSA-26-022-04.

Detection Methods for CVE-2025-26386

Indicators of Compromise

• Unexpected crashes or service failures of the iSTAR Configuration Utility application
• Windows Event Log entries indicating application errors or memory access violations related to ICU processes
• Abnormal network traffic patterns targeting the ICU application ports
• System instability or blue screen errors on hosts running the ICU tool

Detection Strategies

• Monitor for application crashes and unexpected terminations of the ICU tool using endpoint detection and response (EDR) solutions
• Implement network intrusion detection rules to identify malformed or oversized packets targeting ICU services
• Deploy SentinelOne Singularity to detect memory corruption attempts and anomalous process behavior

Monitoring Recommendations

• Enable verbose logging on systems running the iSTAR Configuration Utility to capture crash details and potential exploitation attempts
• Configure alerts for repeated application failures or memory-related errors on ICU host systems
• Monitor network traffic to and from ICU hosts for unusual patterns or connection attempts from unauthorized sources

How to Mitigate CVE-2025-26386

Immediate Actions Required

• Identify all systems running the iSTAR Configuration Utility and their version numbers
• Apply vendor patches as soon as they become available from Johnson Controls
• Restrict network access to ICU hosts to authorized management workstations only
• Ensure users are trained to recognize and avoid social engineering attempts that could trigger exploitation

Patch Information

Johnson Controls has been notified of this vulnerability. Organizations should monitor the Johnson Controls Security Advisory page for official patch releases and remediation guidance. Additionally, the CISA ICS Advisory ICSA-26-022-04 provides additional context and recommendations for addressing this vulnerability.

Workarounds

• Isolate systems running the ICU tool on dedicated management network segments with strict access controls
• Implement application whitelisting to prevent unauthorized programs from executing on ICU host systems
• Consider temporarily disabling network access to ICU installations until patches are available, using local-only configuration when possible
• Deploy host-based intrusion prevention systems (HIPS) to detect and block buffer overflow exploitation attempts

# Network isolation example using Windows Firewall
# Restrict ICU host to accept connections only from authorized management IPs
netsh advfirewall firewall add rule name="Restrict ICU Access" dir=in action=allow remoteip=10.0.100.50,10.0.100.51 enable=yes
netsh advfirewall firewall add rule name="Block Other ICU Access" dir=in action=block program="C:\Program Files\Johnson Controls\ICU\icu.exe" enable=yes