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CVE-2025-8940: Tenda AC20 Buffer Overflow Vulnerability

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Overview

CVE-2025-8940 is a critical vulnerability that has been identified in Tenda AC20 routers, specifically in versions up to 16.03.08.12. This vulnerability arises due to an issue with the strcpy function in the /goform/saveParentControlInfo file. It is a pressing concern as it allows a potential attacker to manipulate the Time argument resulting in a buffer overflow. This vulnerability matters because it can be exploited remotely, which could potentially compromise the entire system or result in data leakage.

Vulnerability Summary

CVE ID: CVE-2025-8940
Severity: Critical, CVSS score of 8.8
Attack Vector: Remote
Privileges Required: None
User Interaction: None
Impact: System compromise and potential data leakage

Affected Products

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Product | Affected Versions

Tenda AC20 | Up to 16.03.08.12

How the Exploit Works

The vulnerability comes into play when the strcpy function is used in the process of saving parental control information. The Time argument, which is used in this function, is not properly checked for its length. This lack of length validation allows an attacker to send a larger than expected input, causing the buffer to overflow. This overflow can be manipulated by a skilled attacker to execute arbitrary code or disrupt the normal functioning of the application.

Conceptual Example Code

The following conceptual code snippet demonstrates how an attacker might exploit this vulnerability. Please note that this is a hypothetical example and should not be used for malicious purposes.

POST /goform/saveParentControlInfo HTTP/1.1
Host: target.example.com
Content-Type: application/json
{
"Time": "A really long string that causes buffer overflow"
}

In the above example, the attacker sends a specially crafted POST request where the Time argument contains an excessively long string, causing a buffer overflow in the strcpy function.
To mitigate this vulnerability, it is advised to apply patches provided by the vendor as soon as possible. In the interim, using Web Application Firewalls (WAF) or Intrusion Detection Systems (IDS) can provide a temporary solution. Regularly updating and patching systems is an effective way to stay protected against such vulnerabilities.

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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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