CVE-2026-2567 Overview
A stack-based buffer overflow vulnerability has been identified in the Wavlink WL-NU516U1 USB 2.0 Wireless Network Adapter firmware version 20251208. This vulnerability exists in the sub_401218 function within the /cgi-bin/nas.cgi file and can be triggered through manipulation of the User1Passwd argument. Successful exploitation allows remote attackers with high privileges to execute arbitrary code or cause denial of service conditions on affected devices.
Critical Impact
Remote attackers can exploit this stack-based buffer overflow to potentially achieve code execution, compromise device integrity, and gain unauthorized control over affected Wavlink network adapters.
Affected Products
- Wavlink WL-NU516U1 Firmware version 20251208
- Wavlink WL-NU516U1 Hardware
Discovery Timeline
- 2026-02-16 - CVE-2026-2567 published to NVD
- 2026-02-18 - Last updated in NVD database
Technical Details for CVE-2026-2567
Vulnerability Analysis
This vulnerability is classified as a stack-based buffer overflow (CWE-787: Out-of-bounds Write, CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the sub_401218 function of the /cgi-bin/nas.cgi CGI script, which handles user authentication parameters. When processing the User1Passwd argument, the function fails to properly validate the length of user-supplied input before copying it to a fixed-size stack buffer.
The vulnerability requires network access and elevated privileges to exploit, but does not require user interaction. Successful exploitation can lead to complete compromise of the device's confidentiality, integrity, and availability. The exploit has been publicly disclosed and proof-of-concept information is available.
Root Cause
The root cause of this vulnerability is improper bounds checking in the password handling function. The sub_401218 function allocates a fixed-size buffer on the stack for the User1Passwd parameter but does not validate that the input length does not exceed the buffer capacity. This allows an attacker to supply an oversized password value that overwrites adjacent stack memory, including the return address, enabling control flow hijacking.
Attack Vector
The attack can be initiated remotely over the network by sending a specially crafted HTTP request to the /cgi-bin/nas.cgi endpoint. The attacker must have high-privilege access to the device's administrative interface. By supplying an excessively long value for the User1Passwd parameter, the attacker can overflow the stack buffer and overwrite critical stack data structures including saved registers and return addresses.
The vulnerability manifests when the CGI script processes the malformed password parameter without adequate length validation. For technical details on the exploitation mechanism, refer to the GitHub security writeup and the VulDB entry.
Detection Methods for CVE-2026-2567
Indicators of Compromise
- Unusual HTTP requests to /cgi-bin/nas.cgi containing abnormally long User1Passwd parameter values
- Device crashes, unexpected reboots, or instability of the Wavlink WL-NU516U1 adapter
- Anomalous network traffic patterns originating from or directed at the affected device
- Signs of unauthorized access or configuration changes on the network adapter
Detection Strategies
- Implement network intrusion detection rules to identify HTTP requests with oversized User1Passwd parameters targeting /cgi-bin/nas.cgi
- Monitor web server logs for suspicious CGI requests with unusually long parameter values
- Deploy network-based anomaly detection to identify potential buffer overflow exploitation attempts
- Conduct regular firmware integrity checks on affected Wavlink devices
Monitoring Recommendations
- Enable verbose logging on network infrastructure to capture traffic to/from Wavlink devices
- Set up alerts for any access attempts to the /cgi-bin/nas.cgi endpoint from untrusted sources
- Monitor for device availability issues that may indicate successful exploitation
- Implement network segmentation monitoring to detect lateral movement from compromised IoT devices
How to Mitigate CVE-2026-2567
Immediate Actions Required
- Restrict network access to the Wavlink WL-NU516U1 administrative interface to trusted IP addresses only
- Place affected devices behind a firewall and disable remote administrative access if not required
- Implement strong access controls and limit administrative privileges on the device
- Monitor vendor communications for security patches addressing this vulnerability
Patch Information
As of the last update on 2026-02-18, no official patch information has been released by Wavlink. Organizations using affected devices should monitor the vendor's official channels for firmware updates. For additional vulnerability details, consult the VulDB CTI Entry and the technical writeup on GitHub.
Workarounds
- Disable remote management features on the Wavlink WL-NU516U1 until a patch is available
- Implement network-level access controls to restrict access to the CGI interface
- Consider replacing vulnerable devices with alternative products if critical security is required
- Deploy a web application firewall (WAF) configured to block requests with oversized parameters
# Example firewall rule to restrict access to vulnerable CGI endpoint
# Adjust interface and IP ranges according to your environment
iptables -A INPUT -p tcp --dport 80 -d <device_ip> -s ! <trusted_network> -j DROP
iptables -A INPUT -p tcp --dport 443 -d <device_ip> -s ! <trusted_network> -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
