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CVE-2025-8939: Buffer Overflow Vulnerability in Tenda AC20 Leading to Potential System Compromise

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Overview

The CVE-2025-8939 is a cybersecurity vulnerability recently discovered in the Tenda AC20 up to 16.03.08.12. This flaw, found in an unidentified function of the file /goform/WifiGuestSet, can potentially enable remote attackers to compromise the system or leak data by exploiting a buffer overflow. As the Tenda AC20 routers are widely used, this vulnerability could have far-reaching consequences, impacting countless systems and networks worldwide. It’s even more critical as the exploit details have been disclosed to the public, increasing the likelihood of potential attacks.

Vulnerability Summary

CVE ID: CVE-2025-8939
Severity: High (8.8 CVSS Severity Score)
Attack Vector: Remote
Privileges Required: None
User Interaction: None
Impact: System compromise or data leakage

Affected Products

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Product | Affected Versions

Tenda AC20 | Versions up to 16.03.08.12

How the Exploit Works

The vulnerability exists due to improper handling of the ‘shareSpeed’ parameter in the /goform/WifiGuestSet file. Attackers can manipulate this parameter to cause a buffer overflow condition. This overflow can then be leveraged to execute arbitrary code on the system or access sensitive information. The attack can be launched remotely and does not require any form of user interaction, making it a dangerous and highly exploitable vulnerability.

Conceptual Example Code

The following is a conceptual example of how this vulnerability might be exploited. This example represents a malicious HTTP POST request to the vulnerable endpoint with a manipulated ‘shareSpeed’ parameter:

POST /goform/WifiGuestSet HTTP/1.1
Host: target.example.com
Content-Type: application/x-www-form-urlencoded
shareSpeed=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA...

In the example above, the ‘shareSpeed’ parameter is overloaded with an excessively long string of ‘A’ characters, triggering a buffer overflow condition. This conceptual example is for illustrative purposes only and does not represent an actual exploit.

Mitigation Guidance

Users of the affected Tenda AC20 routers are advised to apply the vendor-released patch immediately to remedy this vulnerability. In cases where immediate patching is not feasible, implementing Web Application Firewalls (WAFs) or Intrusion Detection Systems (IDS) can serve as temporary mitigation against potential exploits. However, these measures should not replace the need for patching as soon as possible.

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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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