CVE-2025-67189: TOTOLINK A950RG Buffer Overflow Flaw

CVE-2025-67189 Overview

A buffer overflow vulnerability exists in the setParentalRules interface of TOTOLINK A950RG V4.1.2cu.5204_B20210112. The urlKeyword parameter is not properly validated, and the function concatenates multiple user-controlled fields into a fixed-size stack buffer without performing boundary checks. A remote attacker can exploit this flaw to cause denial of service or potentially achieve arbitrary code execution.

Critical Impact

This vulnerability allows unauthenticated remote attackers to execute arbitrary code or cause denial of service on affected TOTOLINK A950RG routers by sending specially crafted requests to the setParentalRules interface.

Affected Products

• TOTOLINK A950RG V4.1.2cu.5204_B20210112

Discovery Timeline

• 2026-02-03 - CVE-2025-67189 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2025-67189

Vulnerability Analysis

This buffer overflow vulnerability (CWE-120: Buffer Copy without Checking Size of Input) affects the parental control functionality of the TOTOLINK A950RG router. The vulnerable code path exists within the setParentalRules interface, which processes user-supplied input without adequate bounds checking.

When a request is made to the setParentalRules endpoint, the handler function allocates a fixed-size buffer on the stack to store concatenated user input. The urlKeyword parameter, along with other user-controlled fields, are concatenated into this buffer using unsafe string operations. Because no length validation is performed before or during the concatenation, an attacker can supply oversized input that overflows the stack buffer.

The network-accessible nature of this vulnerability, combined with the lack of authentication requirements and the potential for arbitrary code execution, makes this a severe security issue for any exposed TOTOLINK A950RG device.

Root Cause

The root cause of this vulnerability lies in the improper handling of user-supplied input in the setParentalRules function. Specifically:

1. The function allocates a fixed-size buffer on the stack
2. Multiple user-controlled parameters including urlKeyword are concatenated into this buffer
3. No boundary checks are performed during the concatenation operation
4. Standard unsafe string functions are used instead of length-limited alternatives

This classic buffer overflow pattern allows attackers to overwrite adjacent stack memory, including saved return addresses, potentially redirecting program execution to attacker-controlled code.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by sending a maliciously crafted HTTP request to the setParentalRules interface with an oversized urlKeyword parameter or other user-controlled fields.

The exploitation process involves sending specially crafted input that exceeds the expected buffer size, causing stack memory corruption. Technical details and proof-of-concept information can be found in the GitHub PoC Repository.

Detection Methods for CVE-2025-67189

Indicators of Compromise

• Unexpected router reboots or crashes indicating potential exploitation attempts
• Unusual network traffic patterns targeting the router's web management interface
• HTTP requests to the setParentalRules endpoint containing abnormally long parameter values
• Suspicious process behavior or unexpected child processes spawned by the router's web service

Detection Strategies

• Monitor HTTP traffic to TOTOLINK A950RG devices for requests to the setParentalRules endpoint with oversized parameters
• Implement network-based intrusion detection rules to identify buffer overflow attack patterns targeting the urlKeyword parameter
• Deploy SentinelOne Singularity to detect anomalous behavior and potential exploitation attempts on network segments containing vulnerable devices
• Review web server logs for requests with unusually long URL parameters or POST data

Monitoring Recommendations

• Enable logging on TOTOLINK A950RG devices and forward logs to a centralized SIEM solution
• Implement network segmentation to isolate IoT devices like routers from critical infrastructure
• Deploy network traffic analysis tools to identify potential exploitation attempts
• Regularly audit firmware versions across all network devices to identify unpatched systems

How to Mitigate CVE-2025-67189

Immediate Actions Required

• Restrict network access to the router's web management interface to trusted IP addresses only
• Disable remote management if not required for operations
• Implement network segmentation to isolate affected devices from critical systems
• Monitor for vendor firmware updates and apply patches as soon as they become available

Patch Information

At the time of publication, no vendor patch has been identified for this vulnerability. Users should monitor TOTOLINK's official channels for security updates addressing CVE-2025-67189. Consider replacing affected devices with supported alternatives if no patch becomes available.

Workarounds

• Disable the web management interface on the WAN side to prevent external exploitation
• Use firewall rules to block external access to the router's management ports
• Implement a VPN solution for remote management instead of exposing the web interface directly
• Consider deploying a network firewall or IPS in front of the affected device to filter malicious requests

# Example firewall rules to restrict access to router management interface
# Block external access to HTTP/HTTPS management ports
iptables -A INPUT -p tcp --dport 80 -i eth0 -j DROP
iptables -A INPUT -p tcp --dport 443 -i eth0 -j DROP

# Allow management only from trusted internal network
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT