CVE-2026-3715: Wavlink WL-WN579X3-C Buffer Overflow Flaw

CVE-2026-3715 Overview

A stack-based buffer overflow vulnerability has been identified in the Wavlink WL-WN579X3-C wireless router firmware version 231124. The vulnerability exists in the sub_40139C function within the /cgi-bin/firewall.cgi file, where improper handling of the del_flag argument allows attackers to overflow the stack buffer. This vulnerability can be exploited remotely by authenticated attackers to potentially execute arbitrary code or cause denial of service conditions on affected devices.

Critical Impact

Remote attackers with low-level authentication can exploit this stack-based buffer overflow to compromise network infrastructure devices, potentially gaining full control over the affected router and the networks it manages.

Affected Products

• Wavlink WL-WN579X3-C Firmware version 231124
• Wavlink WL-WN579X3-C Hardware

Discovery Timeline

• March 8, 2026 - CVE-2026-3715 published to NVD
• March 10, 2026 - Last updated in NVD database

Technical Details for CVE-2026-3715

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the firewall configuration CGI script, specifically within the sub_40139C function. When processing the del_flag argument, the function fails to properly validate the input length before copying data to a fixed-size stack buffer, allowing attackers to write beyond the allocated memory boundaries.

The exploit has been publicly disclosed, increasing the risk of active exploitation. Wavlink responded professionally to the disclosure and released a patched firmware version (20260226) to address this vulnerability.

Root Cause

The root cause stems from insufficient bounds checking in the sub_40139C function when handling user-supplied input via the del_flag parameter. The function allocates a fixed-size buffer on the stack but does not verify that incoming data fits within those bounds before performing memory operations. This classic buffer overflow pattern allows attackers to overwrite adjacent stack memory, including return addresses and saved registers.

Attack Vector

The attack can be initiated remotely over the network against the device's web management interface. An attacker with low-level authentication (basic user access) can craft malicious HTTP requests to the /cgi-bin/firewall.cgi endpoint with an oversized del_flag parameter. No user interaction is required beyond the initial authentication.

The vulnerability manifests in the firewall CGI handler when processing the del_flag argument. The function sub_40139C fails to validate input length before copying user-supplied data to a stack buffer, allowing memory corruption. For detailed technical analysis, refer to the GitHub VulDB Repository.

Detection Methods for CVE-2026-3715

Indicators of Compromise

• Unusual HTTP POST requests to /cgi-bin/firewall.cgi with abnormally large del_flag parameter values
• Router crashes or unexpected reboots coinciding with web interface access attempts
• Anomalous outbound network connections from the router to unknown external IP addresses
• Modified router configuration or firewall rules without administrator action

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests to /cgi-bin/firewall.cgi with oversized parameters
• Monitor router logs for repeated crashes or service restarts in the web management daemon
• Deploy web application firewall rules to block requests containing excessively long parameter values to CGI endpoints
• Establish baseline behavior monitoring for IoT and network devices to detect anomalous activity

Monitoring Recommendations

• Enable verbose logging on network perimeter devices to capture traffic to and from Wavlink routers
• Configure SIEM alerts for any detected buffer overflow attack patterns targeting CGI endpoints
• Periodically audit firmware versions across all Wavlink devices in the network inventory
• Monitor for any unauthorized configuration changes on affected router devices

How to Mitigate CVE-2026-3715

Immediate Actions Required

• Upgrade affected Wavlink WL-WN579X3-C devices to firmware version 20260226 or later immediately
• Restrict access to the router's web management interface to trusted networks only
• Implement network segmentation to isolate vulnerable IoT devices from critical infrastructure
• Consider disabling remote management features until patching is complete

Patch Information

Wavlink has released firmware version 20260226 to address this vulnerability. The patched firmware is available for download from the Wavlink Firmware Download page. The vendor responded professionally to the responsible disclosure and quickly released the fixed version. Administrators should verify firmware integrity after download and apply the update during a scheduled maintenance window.

Workarounds

• Disable remote management access to the router's web interface if firmware update cannot be immediately applied
• Implement access control lists (ACLs) to restrict CGI endpoint access to specific trusted IP addresses only
• Deploy a network firewall rule to filter and inspect traffic destined for the router's management interface
• Monitor the device for signs of compromise while awaiting patch deployment

# Example: Restrict management interface access using upstream firewall
# Block external access to router management on port 80/443
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -j DROP
# Allow management only from trusted admin subnet
iptables -I FORWARD -s 192.168.1.0/24 -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s 192.168.1.0/24 -d <ROUTER_IP> -p tcp --dport 443 -j ACCEPT