CVE-2025-41766: Universal BACnet Router Buffer Overflow

CVE-2025-41766 Overview

CVE-2025-41766 is a stack-based buffer overflow vulnerability affecting MBS Solutions Universal BACnet Router firmware. A low-privileged remote attacker can trigger the buffer overflow via a crafted HTTP POST request using the ubr-network method, resulting in full device compromise. This vulnerability impacts industrial building automation systems that rely on BACnet protocol routing, making it a significant concern for critical infrastructure environments.

Critical Impact

Successful exploitation allows remote attackers with low privileges to achieve complete device compromise through network-accessible HTTP requests, potentially enabling lateral movement across building automation networks.

Affected Products

• MBS Solutions Universal BACnet Router Firmware (all versions)
• MBS Solutions UBR-01 MK II
• MBS Solutions UBR-02
• MBS Solutions UBR-LON

Discovery Timeline

• 2026-03-09 - CVE-2025-41766 published to NVD
• 2026-03-11 - Last updated in NVD database

Technical Details for CVE-2025-41766

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), specifically manifesting as a stack-based buffer overflow in the HTTP request handling functionality of the Universal BACnet Router firmware. The vulnerability exists in the ubr-network method handler, which fails to properly validate the size of user-supplied data before copying it to a fixed-size stack buffer.

Building automation controllers like the affected BACnet routers typically operate with minimal memory protection mechanisms, making stack-based buffer overflows particularly dangerous. When exploited, an attacker can overwrite the return address on the stack, redirecting program execution to attacker-controlled code or achieving arbitrary code execution through return-oriented programming (ROP) techniques.

The network-accessible nature of this vulnerability, combined with the low privilege requirement for exploitation, significantly increases the risk exposure for affected devices deployed in production environments.

Root Cause

The root cause of this vulnerability lies in improper input validation within the HTTP POST request handler for the ubr-network method. The firmware fails to perform adequate bounds checking when processing user-supplied data, allowing oversized input to overflow the designated stack buffer. This is a classic case of insufficient input sanitization in embedded firmware, where memory safety protections common in modern operating systems are often absent.

Attack Vector

The attack is executed remotely over the network via HTTP POST requests. An attacker with low-level credentials or minimal authentication can craft a malicious HTTP POST request targeting the ubr-network endpoint. By including an oversized payload in the request, the attacker can overflow the stack buffer and corrupt adjacent memory regions, including saved return addresses.

The exploitation process involves:

1. Identifying a vulnerable Universal BACnet Router device on the network
2. Authenticating with low-privileged credentials (if required)
3. Sending a crafted HTTP POST request to the ubr-network endpoint with an oversized payload
4. Overwriting the return address to redirect execution flow
5. Achieving arbitrary code execution with firmware-level privileges

Due to the nature of embedded systems, successful exploitation typically grants the attacker complete control over the device, including the ability to intercept and manipulate BACnet traffic, pivot to other devices on the building automation network, or cause denial of service conditions.

Detection Methods for CVE-2025-41766

Indicators of Compromise

• Unusual HTTP POST requests to BACnet router web interfaces, particularly targeting the ubr-network endpoint
• HTTP POST requests with abnormally large payloads exceeding typical operational parameters
• Unexpected device reboots or firmware crashes on affected BACnet routers
• Anomalous network traffic patterns originating from BACnet router devices
• Unauthorized configuration changes on building automation network devices

Detection Strategies

• Monitor HTTP traffic to BACnet router management interfaces for POST requests with oversized body content
• Implement network intrusion detection rules to flag HTTP requests to ubr-network endpoints with payloads exceeding normal thresholds
• Deploy network segmentation and monitor traffic crossing boundaries between IT and OT networks
• Enable logging on building automation controllers where available and centralize log collection

Monitoring Recommendations

• Establish baseline traffic patterns for BACnet router HTTP management interfaces
• Configure alerts for authentication attempts and successful logins to router management interfaces
• Implement continuous monitoring of industrial control system (ICS) network segments for anomalous HTTP activity
• Review device logs regularly for signs of exploitation attempts or unexpected behavior

How to Mitigate CVE-2025-41766

Immediate Actions Required

• Review the MBS Solutions Security Advisory for patch availability and apply updates immediately
• Restrict network access to BACnet router management interfaces using firewall rules or network segmentation
• Disable HTTP management interfaces if not operationally required
• Audit user accounts with access to affected devices and enforce principle of least privilege
• Monitor affected devices for signs of compromise until patches can be applied

Patch Information

MBS Solutions has published a security advisory addressing this vulnerability. Administrators should consult the official vendor advisory for specific firmware update instructions and patch availability for each affected product model. Ensure all Universal BACnet Router devices are updated to the latest firmware version that addresses CVE-2025-41766.

Workarounds

• Isolate affected BACnet routers on dedicated network segments with strict access controls
• Implement firewall rules to block HTTP/HTTPS access to device management interfaces from untrusted networks
• Use VPN or jump hosts to access device management interfaces when remote administration is required
• Disable unnecessary services and protocols on affected devices to reduce attack surface
• Consider deploying a web application firewall (WAF) in front of management interfaces to filter malicious requests

# Example firewall configuration to restrict management interface access
# Restrict HTTP/HTTPS access to BACnet router management interface
iptables -A INPUT -p tcp --dport 80 -s 192.168.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP