CVE-2025-67187: TOTOLINK A950RG Buffer Overflow Flaw

CVE-2025-67187 Overview

A stack-based buffer overflow vulnerability was identified in TOTOLINK A950RG V4.1.2cu.5204_B20210112. The flaw exists in the setIpQosRules interface of /lib/cste_modules/firewall.so where the comment parameter is not properly validated for length. This vulnerability allows remote attackers to execute arbitrary code or cause a denial of service on affected devices without requiring authentication.

Critical Impact

This stack-based buffer overflow can be exploited remotely over the network without authentication, potentially allowing attackers to gain complete control of affected TOTOLINK routers, intercept network traffic, or use compromised devices as pivot points for further attacks.

Affected Products

• TOTOLINK A950RG V4.1.2cu.5204_B20210112
• TOTOLINK A950RG firmware versions prior to security patch

Discovery Timeline

• 2026-02-03 - CVE-2025-67187 published to NVD
• 2026-02-04 - Last updated in NVD database

Technical Details for CVE-2025-67187

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when a program writes more data to a stack-allocated buffer than it can hold. In the case of CVE-2025-67187, the vulnerable code resides within the firewall.so shared library, specifically in the setIpQosRules interface that handles Quality of Service rule configurations.

The comment parameter passed to this interface is not properly validated for length before being copied to a fixed-size stack buffer. When an attacker supplies an overly long string, the excess data overwrites adjacent memory on the stack, including the saved return address. This allows attackers to redirect program execution flow to attacker-controlled code.

The network-accessible nature of this vulnerability combined with no authentication requirements makes it particularly dangerous for internet-facing router deployments. Successful exploitation could result in complete device compromise, allowing attackers to modify router configurations, intercept network traffic, or establish persistent backdoors.

Root Cause

The root cause of this vulnerability is improper input validation in the setIpQosRules function within /lib/cste_modules/firewall.so. The function accepts a comment parameter from user input but fails to perform adequate bounds checking before copying the data into a fixed-size stack buffer. This lack of length validation allows attackers to supply crafted input that exceeds the buffer's allocated size, resulting in a classic stack-based buffer overflow condition.

Attack Vector

The attack can be executed remotely over the network. An attacker can send a specially crafted HTTP request to the router's web management interface targeting the setIpQosRules endpoint. By including an excessively long comment parameter value, the attacker can overflow the stack buffer and overwrite critical memory structures.

The vulnerability does not require user interaction or authentication, meaning any attacker with network access to the router's management interface can attempt exploitation. The attack complexity is low, as standard buffer overflow exploitation techniques can be applied to achieve code execution.

For detailed technical analysis of this vulnerability, refer to the GitHub Buffer Overflow Analysis.

Detection Methods for CVE-2025-67187

Indicators of Compromise

• Unexpected router reboots or crashes that may indicate exploitation attempts
• Anomalous HTTP requests to the router management interface containing unusually long parameter values
• Modified router configurations or unauthorized changes to QoS rules
• Unexpected outbound connections from the router to unknown IP addresses

Detection Strategies

• Monitor HTTP traffic to router management interfaces for requests with oversized comment parameters in setIpQosRules calls
• Implement network intrusion detection rules to identify buffer overflow attack patterns targeting TOTOLINK devices
• Deploy web application firewalls to filter malicious requests before they reach vulnerable endpoints
• Analyze router logs for authentication failures and unusual access patterns to the management interface

Monitoring Recommendations

• Enable comprehensive logging on TOTOLINK routers and forward logs to a centralized SIEM solution
• Configure alerts for any access attempts to the setIpQosRules interface from untrusted networks
• Regularly audit router configurations for unauthorized modifications
• Monitor network traffic for signs of lateral movement originating from router IP addresses

How to Mitigate CVE-2025-67187

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management functionality if not required
• Implement network segmentation to isolate vulnerable devices from critical assets
• Deploy network-based intrusion prevention systems to detect and block exploitation attempts

Patch Information

As of the last NVD update on 2026-02-04, no official vendor patch information has been published for CVE-2025-67187. Users should monitor TOTOLINK's official support channels for firmware updates addressing this vulnerability. Consider replacing affected devices with actively supported alternatives if patches are not made available in a timely manner.

Workarounds

• Configure firewall rules to block external access to the router's management interface on ports 80 and 443
• Use VPN or SSH tunneling to access management interfaces when remote administration is necessary
• Implement strict input validation at the network edge using a web application firewall
• Consider deploying the router behind a more secure gateway device that can filter malicious traffic

# Example: Block external access to router management interface
# Add to upstream firewall or gateway device
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 network
iptables -I FORWARD -s <ADMIN_NETWORK>/24 -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT