CVE-2026-21656

CriticalRCE

Published: 27 February 2026

Published

27 February 2026

Modified

02 March 2026

KEV Added

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Patch

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CVSS Score 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Score 0.0014 33.3th percentile

Risk Priority 20 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2026-21656 is a critical-severity Code Injection (CWE-94) vulnerability in Johnsoncontrols Frick Controls Quantum Hd Firmware. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 33.3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190). What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-10 Information Input Validation good match

prevent

Directly addresses the insufficient input validation causing code injection by requiring checks at input points to prevent malicious code execution.

SI-2 Flaw Remediation good match

prevent

Mandates timely remediation of the known code injection flaw in Quantum HD version 10.22 and prior via patching as advised by CISA and Johnson Controls.

AC-14 Permitted Actions Without Identification or Authentication partial match

prevent

Limits permitted actions without authentication, mitigating pre-authentication code injection impacts by restricting unauthenticated input processing.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

Why these techniques?

The vulnerability allows unauthenticated remote code injection over the network in a public-facing device application, directly mapping to exploitation of public-facing applications.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

NVD Description

Improper Control of Generation of Code ('Code Injection') vulnerability in Johnson Controls Frick Controls Quantum HD allows Code Injection. Insufficient validation of input in certain parameters may permit unexpected actions, which could impact the security of the device before authentication…

occurs.This issue affects Frick Controls Quantum HD version 10.22 and prior.

Deeper analysisAI

CVE-2026-21656 is an Improper Control of Generation of Code ('Code Injection') vulnerability, classified under CWE-94, in Johnson Controls Frick Controls Quantum HD. The flaw arises from insufficient validation of input in certain parameters, enabling code injection that can perform unexpected actions and impact device security before authentication occurs. This issue affects Frick Controls Quantum HD version 10.22 and prior versions.

The vulnerability carries a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), indicating it is exploitable over the network with low attack complexity, no privileges or user interaction required, and unchanged impact scope. Unauthenticated remote attackers can leverage it to inject code, achieving high impacts on confidentiality, integrity, and availability of the affected device.

Advisories from CISA (ICSA-26-057-01) and Johnson Controls' trust center cybersecurity security advisories provide guidance on mitigation. Security practitioners should review these references for details on available patches, workarounds, or other protective measures.