CVE-2025-67188: TOTOLINK A950RG Buffer Overflow Flaw

CVE-2025-67188 Overview

A buffer overflow vulnerability exists in the TOTOLINK A950RG router firmware version V4.1.2cu.5204_B20210112. The vulnerability resides in the setRadvdCfg interface within the /lib/cste_modules/ipv6.so module. Due to improper input validation, the function fails to adequately validate the length of the user-controlled radvdinterfacename parameter, enabling remote attackers to trigger a stack buffer overflow condition. This vulnerability is classified under CWE-120 (Buffer Copy without Checking Size of Input).

Critical Impact
Remote attackers can exploit this buffer overflow vulnerability over the network without authentication, potentially achieving complete compromise of the affected router including arbitrary code execution, device takeover, or denial of service.

Affected Products

TOTOLINK A950RG V4.1.2cu.5204_B20210112
/lib/cste_modules/ipv6.so module
setRadvdCfg interface

Discovery Timeline

2026-02-03 - CVE CVE-2025-67188 published to NVD
2026-02-05 - Last updated in NVD database

Technical Details for CVE-2025-67188

Vulnerability Analysis

This vulnerability represents a classic stack buffer overflow condition resulting from insufficient bounds checking on user-supplied input. The vulnerable code path exists within the IPv6 configuration module of the TOTOLINK A950RG router firmware. When processing requests to the setRadvdCfg interface, the application copies the radvdinterfacename parameter value into a fixed-size stack buffer without verifying that the input length does not exceed the buffer's allocated size.

The network-accessible nature of this vulnerability significantly increases its risk profile, as exploitation requires no prior authentication and can be triggered remotely. Successful exploitation could allow an attacker to overwrite adjacent stack memory, potentially corrupting return addresses or other critical stack data. This could lead to arbitrary code execution with the privileges of the affected process, complete device compromise, or denial of service conditions.

Root Cause

The root cause of CVE-2025-67188 is the absence of proper input length validation in the setRadvdCfg function within the ipv6.so shared library. The function accepts the radvdinterfacename parameter from user input and copies it to a stack-allocated buffer using an unsafe copy operation that does not enforce boundary limits. This classic CWE-120 (Buffer Copy without Checking Size of Input) vulnerability pattern allows attackers to supply input exceeding the buffer's capacity, resulting in memory corruption.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can craft a malicious HTTP request to the setRadvdCfg interface with an oversized radvdinterfacename parameter value. When the router processes this request, the excessive input data overflows the stack buffer, potentially allowing the attacker to:

Overwrite the function's return address to redirect execution flow
Inject and execute arbitrary shellcode
Crash the service causing denial of service
Pivot to further compromise the network

The vulnerability is documented in a GitHub PoC Repository which provides technical details about the exploitation mechanism.

Detection Methods for CVE-2025-67188

Indicators of Compromise

Unexpected crashes or reboots of TOTOLINK A950RG routers
Anomalous HTTP requests to the setRadvdCfg interface containing unusually long radvdinterfacename parameter values
Unusual outbound network connections originating from the router
Modified router configuration or firmware integrity failures

Detection Strategies

Monitor network traffic for HTTP requests targeting the setRadvdCfg endpoint with abnormally large parameter values
Implement intrusion detection rules to identify buffer overflow attack patterns against TOTOLINK devices
Deploy network segmentation to limit exposure of IoT devices to untrusted networks
Enable logging on network perimeter devices to capture suspicious requests to router management interfaces

Monitoring Recommendations

Configure SIEM alerts for repeated access attempts to TOTOLINK router management interfaces from external sources
Monitor for firmware integrity changes using hash verification
Implement network behavior analysis to detect anomalous router activity patterns
Review router access logs regularly for signs of exploitation attempts

How to Mitigate CVE-2025-67188

Immediate Actions Required

Restrict network access to the router's management interface to trusted IP addresses only
Place affected TOTOLINK A950RG routers behind a properly configured firewall
Disable remote management features if not required
Monitor the vendor's website for firmware updates addressing this vulnerability
Consider replacing affected devices if no patch is made available

Patch Information

No vendor patch information is currently available for this vulnerability. Users should monitor TOTOLINK's official channels for security updates addressing CVE-2025-67188. Given the critical severity of this vulnerability, organizations should implement compensating controls until a patch is released.

Workarounds

Disable the IPv6 configuration interface if IPv6 functionality is not required
Implement network-level access controls to restrict access to the router's management interface to specific trusted hosts
Deploy a web application firewall (WAF) or intrusion prevention system (IPS) with rules to block oversized parameter values in requests to the affected endpoint
Isolate affected routers on a separate network segment with restricted access

bash

# Example firewall configuration to restrict management access
# Block external access to router management interface
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP

# Allow only specific trusted management hosts
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.100 -j ACCEPT