CVE-2026-31062: UTT 520W Firmware Buffer Overflow Flaw

CVE-2026-31062 Overview

CVE-2026-31062 is a buffer overflow vulnerability affecting UTT Aggressive 520W router firmware version 1.7.7-180627. The vulnerability exists in the filename parameter of the formFtpServerDirConfig function, which fails to properly validate input length before copying data to a fixed-size buffer. This security flaw allows attackers with adjacent network access and elevated privileges to cause a Denial of Service (DoS) condition by submitting specially crafted input that overflows the buffer and crashes the device.

Critical Impact

Successful exploitation enables attackers on the adjacent network to crash the affected UTT 520W router, disrupting network connectivity for all dependent devices and services.

Affected Products

• UTT 520W Firmware version 1.7.7-180627
• UTT 520W Hardware version 3.0
• UTT Aggressive 520W v3v1 series routers

Discovery Timeline

• April 6, 2026 - CVE-2026-31062 published to NVD
• April 7, 2026 - Last updated in NVD database

Technical Details for CVE-2026-31062

Vulnerability Analysis

This buffer overflow vulnerability (CWE-120: Buffer Copy without Checking Size of Input) resides in the FTP server directory configuration functionality of the UTT 520W router firmware. The formFtpServerDirConfig function accepts a filename parameter from user input but does not implement proper bounds checking before copying the data into an internal buffer. When an attacker supplies input that exceeds the expected buffer size, the excess data overwrites adjacent memory regions, corrupting critical data structures and causing the router to crash.

The vulnerability requires adjacent network access to exploit, meaning the attacker must be on the same network segment as the vulnerable device. Additionally, high privileges are required to access the administrative function containing the vulnerable code. While the attack complexity is low once these prerequisites are met, the impact is limited to availability—there is no evidence that this vulnerability can be leveraged for code execution or information disclosure.

Root Cause

The root cause is a classic buffer overflow condition stemming from the use of unsafe memory copy operations without proper input length validation. The formFtpServerDirConfig function allocates a fixed-size buffer for the filename parameter but fails to verify that incoming data fits within this allocation before performing the copy operation. This represents a violation of secure coding practices where all external input should be validated against expected constraints before processing.

Attack Vector

The attack requires adjacent network positioning and administrative access to the device. An attacker meeting these prerequisites can submit a maliciously crafted HTTP request to the FTP server configuration endpoint with an oversized filename parameter value. The excessive input triggers the buffer overflow condition, corrupting memory and causing the router to crash or become unresponsive.

The vulnerability is documented in the GitHub PoC Documentation, which provides technical details on exploitation methodology. The attack does not require user interaction and can be executed with low complexity once the attacker has the necessary network position and credentials.

Detection Methods for CVE-2026-31062

Indicators of Compromise

• Unexpected router reboots or crashes, particularly following administrative web interface access
• Abnormally long HTTP POST requests to FTP configuration endpoints containing oversized parameter values
• Error logs indicating memory corruption or segmentation faults in the web server process
• Repeated access attempts to /goform/formFtpServerDirConfig or similar FTP configuration endpoints

Detection Strategies

• Monitor HTTP traffic for requests to FTP server configuration endpoints containing unusually large filename parameter values
• Implement intrusion detection rules to flag HTTP requests exceeding normal parameter lengths to administrative interfaces
• Configure logging to capture all administrative function access attempts for forensic analysis
• Deploy network segmentation monitoring to detect unauthorized devices on the administrative network segment

Monitoring Recommendations

• Enable verbose logging on the UTT 520W router to capture configuration change attempts
• Monitor network uptime metrics to identify unexpected device outages that may indicate exploitation attempts
• Implement SNMP trap monitoring to receive immediate alerts when the router becomes unresponsive
• Review administrative access logs regularly for unusual patterns or unauthorized access attempts

How to Mitigate CVE-2026-31062

Immediate Actions Required

• Restrict administrative access to the UTT 520W router to trusted network segments only
• Implement strong authentication and limit administrative credentials to essential personnel
• Deploy network segmentation to isolate management interfaces from general user traffic
• Consider deploying a web application firewall (WAF) or input validation proxy in front of the router's administrative interface

Patch Information

No vendor patch information is currently available for this vulnerability. Administrators should monitor UTT's official channels for firmware updates addressing CVE-2026-31062. Until a patch is released, implementing the workarounds below is strongly recommended to reduce exposure risk.

Workarounds

• Disable FTP server configuration functionality if not required for operations
• Restrict administrative interface access to specific IP addresses using access control lists
• Implement network-level input filtering to block oversized HTTP requests to the router's web interface
• Consider replacing affected devices with alternative hardware that receives regular security updates

# Example: Restrict administrative access via ACL (router-specific syntax may vary)
# Limit web management access to trusted administrative subnet
ip access-list extended MGMT-ACCESS
  permit tcp 192.168.1.0 0.0.0.255 host 192.168.1.1 eq 80
  deny tcp any host 192.168.1.1 eq 80