CVE-2025-3820: Critical Buffer Overflow Vulnerability in Tenda W12 and i24 Routers

Overview

The vulnerability identified as CVE-2025-3820 is a critical security flaw found in Tenda W12 and i24 router models with firmware versions 3.0.0.4(2887) and 3.0.0.5(3644). This vulnerability allows for a stack-based buffer overflow that can be exploited remotely by a malicious actor. It is a significant threat due to its high CVSS severity score of 8.8 and the potential for system compromise or data leakage.
Due to the public disclosure of this exploit, it is now widely accessible to potential attackers, making every router with the affected versions an active target. Therefore, it is crucial for users of these routers to understand the nature of the vulnerability and take immediate steps to mitigate it.

Vulnerability Summary

CVE ID: CVE-2025-3820
Severity: Critical (8.8)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise and data leakage

Affected Products

Product | Affected Versions

Tenda W12 | 3.0.0.4(2887), 3.0.0.5(3644)
Tenda i24 | 3.0.0.4(2887), 3.0.0.5(3644)

How the Exploit Works

The exploit takes advantage of a stack-based buffer overflow vulnerability in the `cgiSysUplinkCheckSet` function of the `bin/httpd` file in the affected routers. By manipulating the `hostIp1/hostIp2` arguments, an attacker can cause the buffer to overflow, potentially allowing them to execute arbitrary code on the device or cause a denial of service.

Conceptual Example Code

Here is a conceptual example of an HTTP request that might exploit this vulnerability:

POST /cgi-bin/httpd?cgiSysUplinkCheckSet HTTP/1.1
Host: [Target IP]
Content-Type: application/x-www-form-urlencoded
hostIp1=192.168.1.1&hostIp2=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

In this example, the `hostIp2` parameter is filled with an excessive number of ‘A’ characters, causing the buffer to overflow.
Please note that this is a conceptual example and should not be used for malicious purposes. The actual exploit may require more complex manipulation, including the use of specific shellcode, to achieve successful execution.

Remediation

Affected users should apply the vendor-provided patch as soon as possible to mitigate this vulnerability. In the meantime, users can deploy a Web Application Firewall (WAF) or Intrusion Detection System (IDS) to monitor and block potential exploit attempts.