KNX Association KNX Protocol Connection Authorization Option 1 Overly Restrictive Account Lockout Mechanism
CVE-2023-4346 is a high-severity overly restrictive account lockout mechanism vulnerability in KNX Protocol Connection Authorization Option 1 from KNX Association, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected KNX Protocol Connection Authorization Option 1 versions: 0. The record does not name a fixed version, so check the vendor advisory. CISA added it to the Known Exploited Vulnerabilities catalogue on July 15, 2026, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Check which version of KNX Protocol Connection Authorization Option 1 you run against the affected versions below, and install the vendor's latest release.
- CISA's required action: 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.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| KNX Association | KNX Protocol Connection Authorization Option 1 | 0 | Not stated |
| Knx | Connection Authorization | Not specified in the record | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.5 | High | CNA (hq.dhs.gov) |
| CVSS 3.1 | 7.5 | High | NVD |
Official description
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Overly Restrictive Account Lockout Mechanism
The product contains an account lockout protection mechanism, but the mechanism is too restrictive and can be triggered too easily, which allows attackers to deny service to legitimate users by causing their accounts to be locked out.
How developers prevent this class of flaw
- Implement more intelligent password throttling mechanisms such as those that take IP address into account, in addition to the login name.
- Implement a lockout timeout that grows as the number of incorrect login attempts goes up, eventually resulting in a complete lockout.
- Consider alternatives to account lockout that would still be effective against password brute force attacks, such as presenting the user machine with a puzzle to solve (making it do some computation).
More Overly Restrictive Account Lockout Mechanism vulnerabilities (CWE-645)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: partial).
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Record last changed materially (score, affected products, status or references).
- Deadline for US federal agencies to remediate, set by CISA.
References
Third-party and government advisories
- cisa.gov/news-events/ics-advisories/icsa-23-236-01Third Party Advisory, US Government Resource
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-4346US Government Resource
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