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CVE-2025-9303: Critical Buffer Overflow Vulnerability in TOTOLINK A720R Router

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Overview

A critical security vulnerability has been identified in the TOTOLINK A720R 4.1.5cu.630_B20250509 router. This vulnerability, indexed as CVE-2025-9303, can potentially allow an attacker to remotely exploit the system, leading to a potential system compromise or data leakage. Given the ubiquity of TOTOLINK routers in home and small business environments, the impact of this vulnerability is widespread and poses a significant risk to information security.

Vulnerability Summary

CVE ID: CVE-2025-9303
Severity: Critical (8.8 CVSS Severity Score)
Attack Vector: Remote
Privileges Required: None
User Interaction: None
Impact: Potential system compromise or data leakage

Affected Products

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Product | Affected Versions

TOTOLINK A720R Router | 4.1.5cu.630_B20250509

How the Exploit Works

This vulnerability stems from a flaw in the function setParentalRules of the file /cgi-bin/cstecgi.cgi. By manipulating the argument ‘desc’, an attacker can cause a buffer overflow condition. This buffer overflow can allow the execution of arbitrary code, meaning an attacker could potentially gain unauthorized access to the system and data stored on the device.

Conceptual Example Code

Here is a conceptual example of how an attacker might exploit this vulnerability in a HTTP request by sending a large amount of data as the ‘desc’ parameter:

POST /cgi-bin/cstecgi.cgi HTTP/1.1
Host: target_router_ip
Content-Type: application/x-www-form-urlencoded
setParentalRules&desc=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA...

In this example, the ‘desc’ parameter is filled with a large number of ‘A’ characters, causing a buffer overflow. The overflow data could contain malicious code that the router inadvertently executes.

Recommendations for Mitigation

Users are strongly urged to apply the vendor-provided patch as soon as possible. Until the patch can be applied, users may use a Web Application Firewall (WAF) or Intrusion Detection System (IDS) as a temporary mitigation measure. These systems can detect and block attempts to exploit this vulnerability. However, they are not a long-term solution and patching the device should be the priority.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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