CVE-2025-41767 Overview
CVE-2025-41767 is an update signature bypass vulnerability affecting MBS Solutions Universal BACnet Router firmware. A high-privileged remote attacker can fully compromise the device by exploiting a flaw in the wwwupdate.cgi method within the web interface. This vulnerability allows attackers to bypass signature verification during firmware updates, potentially enabling the installation of malicious firmware on affected devices.
Critical Impact
Successful exploitation allows complete device compromise through malicious firmware installation, potentially affecting building automation and industrial control systems that rely on BACnet protocol routing.
Affected Products
- MBS Solutions Universal BACnet Router Firmware
- MBS Solutions UBR-01 MK II
- MBS Solutions UBR-02
- MBS Solutions UBR-LON
Discovery Timeline
- 2026-03-09 - CVE-2025-41767 published to NVD
- 2026-03-11 - Last updated in NVD database
Technical Details for CVE-2025-41767
Vulnerability Analysis
This vulnerability is classified under CWE-347 (Improper Verification of Cryptographic Signature). The flaw resides in the firmware update mechanism of the Universal BACnet Router web interface, specifically within the wwwupdate.cgi endpoint. The device fails to properly verify the cryptographic signature of firmware update packages before installation, allowing an authenticated attacker with administrative privileges to upload and install unsigned or maliciously signed firmware.
BACnet routers are commonly deployed in building automation systems, HVAC control, and industrial environments. Compromise of these devices could allow attackers to manipulate building controls, disrupt operations, or establish persistent access within operational technology (OT) networks.
Root Cause
The root cause of CVE-2025-41767 is improper verification of cryptographic signatures during the firmware update process. The wwwupdate.cgi handler fails to adequately validate that firmware packages are signed by a trusted authority before proceeding with installation. This allows specially crafted unsigned or malformed firmware images to bypass security controls intended to prevent unauthorized firmware modifications.
Attack Vector
The attack requires network access to the device's web interface and high-level privileges (administrative access). An attacker with valid administrative credentials can exploit this vulnerability remotely by submitting a malicious firmware update through the wwwupdate.cgi endpoint. The device will process and install the unsigned firmware, granting the attacker full control over the device's functionality and potentially enabling:
- Persistent backdoor installation
- Manipulation of BACnet routing behavior
- Interception of building automation traffic
- Lateral movement within the OT network
The vulnerability mechanism involves uploading a crafted firmware image through the web interface's update functionality. Due to insufficient signature validation in the wwwupdate.cgi handler, the malicious firmware is accepted and installed without proper cryptographic verification. For detailed technical information, refer to the MBS Solutions Security Advisory.
Detection Methods for CVE-2025-41767
Indicators of Compromise
- Unexpected firmware version changes on UBR devices without authorized update procedures
- Unusual HTTP POST requests to /wwwupdate.cgi from unauthorized IP addresses
- Administrative login activity from unfamiliar network locations
- Modified device behavior or configuration changes not aligned with authorized maintenance
Detection Strategies
- Monitor web server logs on UBR devices for requests to /wwwupdate.cgi endpoint
- Implement network monitoring to detect firmware update traffic to BACnet router devices
- Establish firmware version baselines and alert on unauthorized changes
- Deploy network segmentation to isolate BACnet devices and monitor cross-segment traffic
Monitoring Recommendations
- Enable logging on all administrative interfaces of affected devices
- Configure SIEM rules to alert on firmware update attempts outside maintenance windows
- Perform regular firmware integrity verification using known-good hashes
- Monitor for authentication attempts to device web interfaces from unexpected sources
How to Mitigate CVE-2025-41767
Immediate Actions Required
- Review and restrict administrative access to affected UBR devices
- Implement network segmentation to limit access to device management interfaces
- Audit recent firmware updates on affected devices to verify integrity
- Enforce strong authentication and limit administrative accounts to essential personnel only
Patch Information
MBS Solutions has released a security advisory addressing this vulnerability. Organizations should consult the MBS Solutions Security Advisory for official patch information and updated firmware versions that address the signature bypass vulnerability.
Workarounds
- Restrict network access to the device web interface using firewall rules or VLANs
- Disable remote firmware update functionality if not operationally required
- Implement additional authentication layers such as VPN access for administrative functions
- Monitor and log all access attempts to the wwwupdate.cgi endpoint
# Example: Restrict access to UBR web interface using iptables
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
