Johnson Controls CEM AC2000

Summary

A high-severity DLL hijacking vulnerability (CVE-2026-21661, CVSS 8.7) has been discovered in Johnson Controls CEM AC2000 versions 12.0, 11.0, and 10.6. The flaw allows standard users to escalate privileges on affected systems through uncontrolled search path exploitation (CWE-427). Johnson Controls has released patched versions (12.0 Release 10, 11.0 Release 9, 10.6 Release 3) and CISA recommends organizations isolate control systems behind firewalls and apply mitigations immediately.

Full text

ICS Advisory Johnson Controls CEM AC2000 Release DateMay 05, 2026 Alert CodeICSA-26-125-05 Related topics: Industrial Control System Vulnerabilities, Industrial Control Systems View CSAF Summary Successful exploitation of this vulnerability could allow a standard user to escalate privileges on the host machine. The following versions of Johnson Controls CEM AC2000 are affected: CEM AC2000 12.0 (CVE-2026-21661) CEM AC2000 11.0 (CVE-2026-21661) CEM AC2000 10.6 (CVE-2026-21661) CVSS Vendor Equipment Vulnerabilities v3 8.7 Johnson Controls Inc. Johnson Controls CEM AC2000 Uncontrolled Search Path Element Background Critical Infrastructure Sectors: Critical Manufacturing, Commercial Facilities, Government Services and Facilities, Transportation Systems, Energy Countries/Areas Deployed: Worldwide Company Headquarters Location: Ireland Vulnerabilities Expand All + CVE-2026-21661 The affected product is vulnerable to DLL hijacking, which could allow an attacker to escalate standard user privileges on the host machine. View CVE Details Affected Products Johnson Controls CEM AC2000 Vendor:Johnson Controls Inc. Product Version:Johnson Controls Inc. CEM AC2000: 12.0, Johnson Controls Inc. CEM AC2000: 11.0, Johnson Controls Inc. CEM AC2000: 10.6 Product Status:known_affected Remediations MitigationJohnson Controls recommends users apply the following mitigations: MitigationUpgrade CEM AC 2000 12.0 to 12.0 Release 10. MitigationUpgrade CEM AC 2000 11.0 to 11.0 Release 9. MitigationUpgrade CEM AC 2000 10.6 to 10.6 Release 3. MitigationFor more detailed mitigation instructions, please see Johnson Controls Product Security Advisory.https://www.johnsoncontrols.com/trust-center/cybersecurity/security-advisories Relevant CWE: CWE-427 Uncontrolled Search Path Element Metrics CVSS Version Base Score Base Severity Vector String 3.1 8.7 HIGH CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L Acknowledgments Tom Hulme of CSACyber reported this vulnerability to Johnson Controls Legal Notice and Terms of Use This product is provided subject to this Notification (https://www.cisa.gov/notification) and this Privacy & Use policy (https://www.cisa.gov/privacy-policy). Recommended Practices CISA recommends users take defensive measures to minimize the risk of exploitation of this vulnerability. Minimize network exposure for all control system devices and/or systems, ensuring they are not accessible from the internet. Locate control system networks and remote devices behind firewalls and isolating them from business networks. When remote access is required, use more secure methods, such as Virtual Private Networks (VPNs), recognizing VPNs may have vulnerabilities and should be updated to the most current version available. Also recognize VPN is only as secure as the connected devices. CISA reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures. CISA also provides a section for control systems security recommended practices on the ICS webpage on cisa.gov/ics. Several CISA products detailing cyber defense best practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies. CISA encourages organizations to implement recommended cybersecurity strategies for proactive defense of ICS assets. Additional mitigation guidance and recommended practices are publicly available on the ICS webpage at cisa.gov/ics in the technical information paper, ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation Strategies. Organizations observing suspected malicious activity should follow established internal procedures and report findings to CISA for tracking and correlation against other incidents. CISA also recommends users take the following measures to protect themselves from social engineering attacks: Do not click web links or open attachments in unsolicited email messages. Refer to Recognizing and Avoiding Email Scams for more information on avoiding email scams. Refer to Avoiding Social Engineering and Phishing Attacks for more information on social engineering attacks. No known public exploitation specifically targeting this vulnerability has been reported to CISA at this time. This vulnerability is not exploitable remotely. Revision History Initial Release Date: 2026-05-05 Date Revision Summary 2026-05-05 1 Initial Republication of Johnson Controls product security advisory. Legal Notice and Terms of Use This product is provided subject to this Notification and this Privacy & Use policy. Vendor Johnson Controls Tags Sector: Communications Sector, Critical Manufacturing Sector, Energy Sector, Government Services and Facilities Sector, Transportation Systems Sector Topics: Industrial Control System Vulnerabilities, Industrial Control Systems Please share your thoughts We recently updated our anonymous product survey; we welcome your feedback. Related Advisories May 05, 2026 ICS Advisory | ICSA-26-125-04 ABB B&R Automation Studio May 05, 2026 ICS Advisory | ICSA-26-125-01 Hitachi Energy PCM600 May 05, 2026 ICS Advisory | ICSA-26-125-03 ABB B&R Automation Runtime May 05, 2026 ICS Advisory | ICSA-26-125-02 ABB B&R PVI

Indicators of Compromise

• cve — CVE-2026-21661

Entities