CVE-2026-1139: UTT 520W Buffer Overflow Vulnerability

CVE-2026-1139 Overview

A buffer overflow vulnerability has been identified in UTT 进取 520W router firmware version 1.7.7-180627. This vulnerability affects the strcpy function within the /goform/ConfigExceptMSN endpoint, allowing attackers to exploit improper memory bounds checking to overflow buffer boundaries. The vulnerability can be exploited remotely over the network by authenticated users, potentially leading to arbitrary code execution, system compromise, or denial of service conditions on affected devices.

Critical Impact

Remote attackers with low-privilege access can exploit this buffer overflow vulnerability to potentially execute arbitrary code or cause system crashes on UTT 进取 520W routers, compromising network infrastructure security.

Affected Products

• UTT 进取 520W firmware version 1.7.7-180627
• UTT 进取 520W devices with vulnerable /goform/ConfigExceptMSN endpoint

Discovery Timeline

• January 19, 2026 - CVE-2026-1139 published to NVD
• January 19, 2026 - Last updated in NVD database

Technical Details for CVE-2026-1139

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw exists in the handling of user-supplied input within the /goform/ConfigExceptMSN endpoint of the UTT 进取 520W router's web management interface.

The vulnerable code utilizes the strcpy function to copy user-controlled data without proper bounds checking. When an attacker submits a specially crafted request with an oversized input string, the function copies beyond the allocated buffer boundaries, corrupting adjacent memory regions. This memory corruption can overwrite critical data structures, function pointers, or return addresses on the stack.

The network-accessible nature of this vulnerability significantly increases the attack surface, as any authenticated user on the network can potentially reach the vulnerable endpoint. The exploit has been publicly disclosed, which raises the urgency for remediation.

Root Cause

The root cause of this vulnerability is the unsafe use of the strcpy function in the /goform/ConfigExceptMSN handler. The strcpy function does not perform any bounds checking and will continue copying data until it encounters a null terminator, regardless of the destination buffer size. When user-supplied input exceeds the expected buffer length, memory corruption occurs. Proper input validation and use of safer string handling functions such as strncpy or snprintf would prevent this vulnerability.

Attack Vector

The attack vector is network-based, requiring low-privilege authentication. An attacker can exploit this vulnerability by sending malicious HTTP requests to the /goform/ConfigExceptMSN endpoint with carefully crafted oversized parameters. The manipulation triggers a buffer overflow condition that could allow:

1. Code Execution: Overwriting return addresses to redirect execution flow to attacker-controlled code
2. Denial of Service: Crashing the device's web service or causing a complete system reboot
3. Information Disclosure: Potentially leaking memory contents through controlled overflow operations

The exploitation of this vulnerability has been publicly documented. For technical details, refer to the GitHub CVE Documentation and VulDB entry #341730.

Detection Methods for CVE-2026-1139

Indicators of Compromise

• Unusual or malformed HTTP POST requests to /goform/ConfigExceptMSN containing abnormally long parameter values
• Unexpected router reboots or web interface crashes following configuration change attempts
• Anomalous network traffic patterns originating from or destined to the router's management interface
• System logs showing segmentation faults or memory access violations in the web server process

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests with oversized parameters targeting /goform/ConfigExceptMSN
• Monitor for repeated authentication attempts followed by requests to the vulnerable endpoint
• Deploy web application firewall rules to block requests with excessively long input strings to UTT router management interfaces
• Enable and review device logs for service crashes or unexpected restarts

Monitoring Recommendations

• Configure alerting for any access attempts to /goform/ConfigExceptMSN from untrusted network segments
• Implement network segmentation to isolate router management interfaces from general user traffic
• Establish baseline behavior monitoring for router management interface access patterns
• Deploy SentinelOne Singularity for network visibility to detect exploitation attempts targeting embedded devices

How to Mitigate CVE-2026-1139

Immediate Actions Required

• Restrict network access to the UTT 进取 520W router's web management interface using firewall rules
• Limit management interface access to trusted IP addresses and network segments only
• Disable remote management access if not strictly required for operations
• Monitor for and investigate any suspicious activity targeting the /goform/ConfigExceptMSN endpoint

Patch Information

At the time of disclosure, the vendor (UTT) was contacted but did not respond regarding this vulnerability. No official patch is currently available. Organizations should implement compensating controls and monitor for future firmware updates from the vendor.

For additional vulnerability details, consult:

• GitHub CVE Documentation
• VulDB Entry #341730

Workarounds

• Implement strict access control lists (ACLs) to limit management interface access to authorized administrator IP addresses only
• Place the router's management interface on an isolated management VLAN inaccessible from the general network
• Consider deploying a reverse proxy or web application firewall with input length restrictions in front of the management interface
• Evaluate replacing affected devices with alternatives from vendors that provide timely security patches

# Example firewall rule to restrict management interface access (iptables)
# Allow management access only from trusted admin network 192.168.100.0/24
iptables -A INPUT -p tcp --dport 80 -s 192.168.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP