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
A new way to communicate
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Message, call, share files, and coordinate with identities kept separate.
- • Encrypted identity
- • Ameeba Chat authenticates access
- • Aliases and categories
- • End-to-end encrypted chat, calls, and files
- • Secure notes for sensitive information
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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.