CVE-2023-4346 — KNX Association KNX Protocol Connection Authorization Option 1 | CVSS 7.5 HIGH

HIGH

CVSS 7.5 HIGH  ·  EPSS 0%  ·  KNX Association KNX Protocol Connection Authorization Option 1

Severity Overview

Summary

KNX devices that use KNX Connection Authorization and support Option 1 are, depending on the implementation, vulnerable to being locked and users being unable to reset them to gain access to the device. The BCU key feature on the devices can be used to create a password for the device, but this password can often not be reset without entering the current password. If the device is configured to interface with a network, an attacker with access to that network could interface with the KNX installation, purge all devices without additional security options enabled, and set a BCU key, locking the device. Even if a device is not connected to a network, an attacker with physical access to the device could also exploit this vulnerability in the same way.

What the Attack Looks Like

If successfully exploited: High availability impact means the vulnerability can also cause a denial of service, which may be used for disruption or as a diversion during a broader attack.

Analyst Takeaway

The attack is launched over the network (remotely exploitable without physical access) and no authentication is required. This vulnerability is already in CISA KEV, which means exploitation has been confirmed in the wild — treat this as active risk, not theoretical exposure. In parallel with patching, defenders should review external exposure, hunt for signs of exploitation, and validate whether compensating controls are in place for vulnerable assets.

MITRE ATT&CK Mapping

• T1203 – Exploitation for Client Execution
  Rationale: The vulnerability appears tied to a client application such as a browser, document handler, or end-user productivity software.

Detection Guidance

• T1203 — Exploitation for Client Execution
  • Inspect endpoint telemetry for suspicious execution chains: scripting engines or download utilities launched as children of browsers, Office applications, PDF readers, or other client-side software.
  • Look for LOLBin usage (certutil, mshta, rundll32, regsvr32, wmic) with suspicious arguments spawned from document-handling parent processes.
  • Review email attachment and file download activity correlated with any suspicious process execution on the same endpoint within the same time window.

Hunting Considerations

These are proactive hunts mapped to the ATT&CK techniques identified for this CVE. Run them now — do not wait for an alert to fire.

• T1203 — Exploitation for Client Execution
  • Parent-child process chains: Search for scripting engines (PowerShell, cmd.exe, wscript.exe, cscript.exe, mshta.exe) or download utilities (certutil, bitsadmin, curl) spawned as direct children of Office applications, browsers, or PDF readers. These chains are rarely legitimate.
  • LOLBin execution: Hunt for Living-off-the-Land Binaries — regsvr32, rundll32, mshta, certutil, wmic, odbcconf — executing from unusual working directories or with command lines containing encoded strings, remote paths, or -enc / -nop / IEX patterns.
  • Network connections from client apps: Flag outbound connections to new external IPs from browser, Office, or document-handling processes that do not match known CDN or update infrastructure. These indicate the exploited process reaching out for a secondary payload.
  • Windows Event IDs: Event 4688 (process creation with full command line) and Sysmon Event 1 are your primary sources. Filter for suspicious parent-child pairs. Sysmon Event 3 (network connection) from document handlers is a high-fidelity indicator.
  • Correlation with delivery: Check email gateway and proxy logs for attachment opens or file downloads on the same host in the 30 minutes before any suspicious process execution — this helps confirm the initial delivery vector.

Recommended Actions

Immediate (0–24 Hours)

• Inventory: Identify all systems running KNX Association KNX Protocol Connection Authorization Option 1. Include production, staging, dev, and cloud environments — untracked instances are the most likely to remain unpatched.
• Validate internet-facing exposure: Determine which of the affected systems are reachable from the public internet. Prioritize these for immediate remediation or compensating controls.

Remediation

• Apply the vendor patch: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
• CISA directive deadline: 2026-07-29 — this is the mandatory deadline for US federal civilian agencies under BOD 22-01. All organizations should treat this date as a strong target regardless of federal mandate.
• Verify remediation: After patching, confirm the correct version is installed on all affected hosts. Run a vulnerability scan or use your asset management tooling to verify — do not rely solely on change tickets.

Detection Coverage

• Verify ATT&CK coverage: Confirm your SIEM and EDR have detection logic in place for T1203. Review the Detection Guidance and Hunting Considerations sections of this alert for the specific log sources and behavioral patterns to monitor.
• Unauthenticated exploitation monitoring: Because this vulnerability requires no authentication, internet-facing scanning and exploitation attempts may begin within hours of public disclosure. Ensure alerting is in place before the end of the day.
• Threat intelligence feeds: Monitor your TI feeds and vendor advisory channels for published indicators of compromise (IOCs), proof-of-concept exploit releases, or active campaign reporting associated with this CVE — these should trigger an immediate hunt even if no internal alerts have fired.

Detection Playbooks

Vulnerability Details

Additional Notes

https://www.cisa.gov/news-events/ics-advisories/icsa-23-236-01 ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2023-4346