CVE-2025-61128: WAVLINK Router Buffer Overflow Vulnerability

CVE-2025-61128 Overview

A critical stack-based buffer overflow vulnerability has been identified in WAVLINK QUANTUM D3G/WL-WN530HG3 router firmware version M30HG3_V240730. This vulnerability allows remote attackers to execute arbitrary code by sending a specially crafted HTTP POST request with a malicious referrer value to the login.cgi endpoint. The flaw exists in the firmware's handling of the referrer header during authentication requests, where insufficient bounds checking allows attackers to overflow a stack buffer and potentially gain complete control over the affected device.

Critical Impact

Unauthenticated remote attackers can execute arbitrary code on vulnerable WAVLINK routers, potentially leading to complete device compromise, network infiltration, and use of the device in botnet operations.

Affected Products

• WAVLINK QUANTUM D3G (WL-WN530HG3) with firmware version M30HG3_V240730
• Potentially other WAVLINK router models with similar firmware implementations

Discovery Timeline

• 2025-10-28 - CVE-2025-61128 published to NVD
• 2025-10-30 - Last updated in NVD database

Technical Details for CVE-2025-61128

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when the login.cgi handler processes HTTP POST requests without properly validating the length of the referrer header value. When an attacker sends an HTTP POST request to the login endpoint with an oversized or specially crafted referrer value, the firmware copies this data into a fixed-size stack buffer without adequate bounds checking. This allows the attacker to overwrite adjacent stack memory, including the return address, enabling control flow hijacking and arbitrary code execution.

The vulnerability is particularly severe in the context of IoT/embedded devices because WAVLINK routers typically run with elevated privileges, and successful exploitation grants the attacker full control over the network appliance. This can be leveraged for persistent network access, traffic interception, or enrollment of the device into botnets targeting other infrastructure.

Root Cause

The root cause of this vulnerability lies in unsafe string handling within the login.cgi CGI script or its underlying processing functions. The firmware fails to validate the length of user-supplied input in the HTTP referrer header before copying it to a stack-allocated buffer. This classic buffer overflow pattern allows attackers to inject shellcode or ROP chains that execute with the privileges of the web server process running on the router.

Attack Vector

The attack is conducted over the network by sending a malicious HTTP POST request to the router's web administration interface, specifically targeting the /login.cgi endpoint. The attacker crafts a request containing an oversized or malformed referrer header value designed to overflow the stack buffer. Since no authentication is required to reach the vulnerable code path, this represents a pre-authentication remote code execution vulnerability.

The exploitation involves sending an HTTP POST request with a crafted referrer header that exceeds the expected buffer size, overwriting the saved return address on the stack. By carefully constructing the overflow payload, an attacker can redirect program execution to shellcode or leverage return-oriented programming techniques to achieve arbitrary code execution.

Technical details and a proof-of-concept are available in the GitHub Gist PoC Code published by the security researcher.

Detection Methods for CVE-2025-61128

Indicators of Compromise

• Unusual HTTP POST requests to /login.cgi with abnormally large referrer header values
• Unexpected outbound connections from WAVLINK router devices to unknown IP addresses
• Router configuration changes or unauthorized administrative access
• Presence of unknown processes or services running on the affected device

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests with oversized referrer headers targeting WAVLINK device endpoints
• Monitor for anomalous traffic patterns originating from router management interfaces
• Deploy web application firewall rules to block malformed HTTP requests to CGI endpoints

Monitoring Recommendations

• Enable logging on WAVLINK routers if available and monitor for authentication anomalies
• Implement network segmentation to isolate IoT devices from critical infrastructure
• Use network monitoring tools to detect unusual traffic volumes or connection patterns from router devices

How to Mitigate CVE-2025-61128

Immediate Actions Required

• Restrict access to the router's web administration interface by IP address or disable remote management if not required
• Place affected WAVLINK routers behind a firewall that blocks external access to the management interface
• Monitor WAVLINK's official channels for firmware updates addressing this vulnerability
• Consider replacing affected devices with alternatives from vendors with better security track records if patches are not available

Patch Information

At the time of publication, no official patch information is available from WAVLINK. Users should monitor the vendor's support website and apply firmware updates as soon as they become available. Given the critical nature of this vulnerability, organizations should prioritize network isolation of affected devices until patches are released.

Workarounds

• Disable the web administration interface entirely if it is not required for operations
• Implement strict firewall rules to allow management interface access only from trusted internal IP addresses
• Enable any available access control features on the router to limit exposure
• Consider network-level protections such as VPN-only access to the management interface

# Example iptables rule to restrict access to router management interface
# Apply on upstream firewall or network gateway
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 only from trusted management subnet
iptables -I FORWARD -s 192.168.1.0/24 -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT