CVE-2026-21657

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-2026-21657 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

SI-10 directly addresses the root cause of CVE-2026-21657 by requiring comprehensive input validation to prevent code injection from insufficiently validated parameters.

SI-2 Flaw Remediation good match

prevent

SI-2 ensures timely patching and flaw remediation as outlined in the vendor and CISA advisories, preventing exploitation of the code injection vulnerability in affected versions.

AC-14 Permitted Actions Without Identification or Authentication partial match

prevent

AC-14 limits permitted actions without authentication, mitigating pre-authentication code injection that impacts device security via unexpected actions on unauthenticated inputs.

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 is a pre-authentication code injection flaw in a network-accessible ICS device, directly enabling exploitation of a public-facing application.

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-2026-21657 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, which may permit unexpected actions that impact the security of the device 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 remotely over the network by unauthenticated attackers requiring low complexity and no user interaction. Successful exploitation enables code injection, resulting in high impacts to confidentiality, integrity, and availability of the affected device.

Mitigation details are outlined in the CISA ICS Advisory ICSA-26-057-01 (https://www.cisa.gov/news-events/ics-advisories/icsa-26-057-01) and the Johnson Controls security advisory (https://www.johnsoncontrols.com/trust-center/cybersecurity/security-advisories).