CVE-2026-2565: Wavlink WL-NU516U1 Buffer Overflow Flaw

CVE-2026-2565 Overview

A stack-based buffer overflow vulnerability has been identified in Wavlink WL-NU516U1 firmware version 20251208. This firmware vulnerability affects the function sub_40785C within the file /cgi-bin/adm.cgi, where manipulation of the time_zone argument can trigger a buffer overflow condition. While the attack can be initiated remotely over the network, successful exploitation requires high privileges and is considered to have high complexity, making the exploitation difficult to execute.

Critical Impact

Successful exploitation of this stack-based buffer overflow could allow an authenticated attacker with elevated privileges to achieve remote code execution, potentially compromising the confidentiality, integrity, and availability of the affected Wavlink device.

Affected Products

• Wavlink WL-NU516U1 Firmware version 20251208
• Wavlink WL-NU516U1 hardware device

Discovery Timeline

• 2026-02-16 - CVE-2026-2565 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2026-2565

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), a fundamental memory safety issue affecting embedded network devices. The vulnerable function sub_40785C in the CGI binary /cgi-bin/adm.cgi fails to properly validate the length of user-supplied input for the time_zone parameter before copying it to a stack-allocated buffer.

The vendor was contacted early about this disclosure but did not respond in any way, leaving affected devices without an official remediation path. The exploit has been made available to the public, which increases the risk of malicious exploitation despite the high complexity required for successful attacks.

Root Cause

The root cause of CVE-2026-2565 lies in insufficient bounds checking when processing the time_zone argument within the sub_40785C function. When an oversized time_zone value is submitted through the /cgi-bin/adm.cgi endpoint, the function copies the input data to a fixed-size stack buffer without validating whether the input exceeds the buffer's capacity. This classic stack-based buffer overflow pattern can corrupt adjacent memory, including saved return addresses and stack canaries if present.

Attack Vector

The attack vector for this vulnerability is network-based, requiring the attacker to have remote access to the device's administrative CGI interface. The exploitation scenario involves:

1. An authenticated attacker with high-level privileges accessing the /cgi-bin/adm.cgi endpoint
2. Submitting a crafted HTTP request with an oversized time_zone parameter value
3. The malicious input triggers a stack buffer overflow in the sub_40785C function
4. Depending on memory layout and exploit sophistication, this could lead to arbitrary code execution

The attack is characterized by high complexity, meaning specific conditions must be met for successful exploitation, such as bypassing any memory protection mechanisms and crafting precise payloads. Technical details regarding the vulnerability mechanism are available in the GitHub documentation for Wavlink.

Detection Methods for CVE-2026-2565

Indicators of Compromise

• Anomalous HTTP requests to /cgi-bin/adm.cgi containing unusually long time_zone parameter values
• Unexpected device reboots or crashes following administrative interface access
• Modified firmware or configuration files on the Wavlink device
• Unauthorized processes or network connections originating from the device

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests with oversized time_zone parameters targeting CGI endpoints
• Deploy web application firewall (WAF) rules to block requests containing abnormally long input values to administrative interfaces
• Monitor for unusual traffic patterns or authentication attempts against Wavlink device management interfaces
• Correlate device logs with network flow data to identify potential exploitation attempts

Monitoring Recommendations

• Enable verbose logging on all Wavlink devices and forward logs to a centralized SIEM platform
• Implement anomaly detection for HTTP request sizes and parameter lengths targeting embedded device interfaces
• Monitor device health metrics such as unexpected restarts, memory usage spikes, or CPU anomalies
• Establish baseline network behavior for Wavlink devices to detect deviations indicative of compromise

How to Mitigate CVE-2026-2565

Immediate Actions Required

• Restrict network access to the Wavlink WL-NU516U1 administrative interface using firewall rules or network segmentation
• Limit administrative access to trusted IP addresses and implement strong authentication controls
• Consider isolating affected devices on a separate VLAN with restricted internet access
• Monitor for any indicators of compromise as detailed above
• Evaluate replacing the affected device with a supported alternative if the vendor does not release a patch

Patch Information

As of the last NVD update on 2026-02-18, no official patch has been released by Wavlink. The vendor was contacted early about this disclosure but did not respond. Users should monitor the VulDB entry #346172 and vendor channels for potential security updates. Until a patch becomes available, implementing the recommended workarounds is critical.

Workarounds

• Disable remote management access to the device and only allow local administration when necessary
• Implement strict input validation at the network perimeter using a reverse proxy or WAF to sanitize requests
• Deploy network-level access controls (ACLs) to restrict which hosts can communicate with the device's management interface
• Consider deploying an intrusion prevention system (IPS) to block requests matching known exploitation patterns

# Example: iptables rules to restrict access to device management interface
# Replace 192.168.1.100 with your Wavlink device IP
# Replace 192.168.1.10 with your trusted admin workstation IP

iptables -A INPUT -d 192.168.1.100 -p tcp --dport 80 -s 192.168.1.10 -j ACCEPT
iptables -A INPUT -d 192.168.1.100 -p tcp --dport 80 -j DROP
iptables -A INPUT -d 192.168.1.100 -p tcp --dport 443 -s 192.168.1.10 -j ACCEPT
iptables -A INPUT -d 192.168.1.100 -p tcp --dport 443 -j DROP