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CVE-2025-11091: Remote Buffer Overflow Vulnerability in Tenda AC21 Router

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Overview

A significant security vulnerability, identified as CVE-2025-11091, has recently been discovered in Tenda AC21 routers up to version 16.03.08.16. This vulnerability specifically affects the function ‘sscanf’ of the file ‘/goform/SetStaticRouteCfg’, leading to a buffer overflow. The flaw is of critical concern as it allows remote attackers to potentially compromise systems and leak sensitive data. Given the widespread use of Tenda AC21 routers, this vulnerability poses a substantial threat to both individual users and organizations alike.

Vulnerability Summary

CVE ID: CVE-2025-11091
Severity: High (8.8 CVSS v3)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: System compromise and potential data leakage

Affected Products

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Product | Affected Versions

Tenda AC21 | Up to 16.03.08.16

How the Exploit Works

The vulnerability lies in the improper handling of arguments by the ‘sscanf’ function in the ‘/goform/SetStaticRouteCfg’ file. By manipulating the argument list, an attacker can trigger a buffer overflow condition. This overflow allows the attacker to execute arbitrary code, possibly leading to a complete system compromise or the leakage of sensitive data.

Conceptual Example Code

An attacker might exploit this vulnerability by sending a specially crafted HTTP request, as illustrated in this conceptual example:

POST /goform/SetStaticRouteCfg HTTP/1.1
Host: target_router_ip
Content-Type: application/x-www-form-urlencoded
routeName=Default+Route&routeDest=0.0.0.0&routeMask=0.0.0.0&routeGateway=x.x.x.x&routeMetric=1&routeInf=br0%00{payload}

In this example, `{payload}` represents a maliciously crafted sequence of bytes designed to overflow the buffer and execute arbitrary code.

Recommended Mitigations

To protect against this vulnerability, users are advised to apply the patch provided by the vendor as soon as it becomes available. In the interim, users can mitigate the risk by implementing a Web Application Firewall (WAF) or an Intrusion Detection System (IDS) to detect and block attempts to exploit this vulnerability.

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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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