CVE-2025-3693: Tenda W12 Buffer Overflow Vulnerability

CVE-2025-3693 Overview

A critical stack-based buffer overflow vulnerability has been identified in the Tenda W12 wireless router firmware version 3.0.0.5. The vulnerability exists within the cgiWifiRadioSet function located in the /bin/httpd binary. Improper bounds checking during input processing allows attackers to manipulate data in a way that triggers a buffer overflow condition on the stack. This vulnerability can be exploited remotely over the network, potentially allowing attackers to execute arbitrary code, crash the device, or gain unauthorized control over the affected router.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to compromise Tenda W12 routers, potentially gaining complete control of the device and using it as a pivot point for further network attacks.

Affected Products

• Tenda W12 Firmware version 3.0.0.5
• Tenda W12 Hardware Device

Discovery Timeline

• April 16, 2025 - CVE-2025-3693 published to NVD
• July 16, 2025 - Last updated in NVD database

Technical Details for CVE-2025-3693

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The vulnerable function cgiWifiRadioSet in the /bin/httpd binary fails to properly validate the length of user-supplied input before copying it to a fixed-size buffer allocated on the stack. When an attacker provides input exceeding the expected buffer size, the overflow overwrites adjacent memory on the stack, including potentially critical data such as return addresses and saved frame pointers.

The exploit has been publicly disclosed, increasing the risk of widespread attacks against unpatched devices. Given that this is a network-accessible vulnerability requiring low privileges to exploit, it presents a significant threat to enterprise and home networks using the affected Tenda W12 router.

Root Cause

The root cause of this vulnerability lies in the inadequate input validation within the cgiWifiRadioSet function. The function handles HTTP requests related to WiFi radio configuration settings but does not implement proper bounds checking when processing user-supplied parameters. This allows oversized input to overwrite the stack buffer boundaries, leading to memory corruption.

The lack of modern exploit mitigations commonly found in embedded device firmware (such as stack canaries, ASLR, or non-executable stack protections) may further increase the exploitability of this vulnerability.

Attack Vector

The attack vector for CVE-2025-3693 is network-based, allowing remote exploitation without physical access to the device. An attacker with low-level privileges (such as basic network access) can craft malicious HTTP requests targeting the /bin/httpd web server on the Tenda W12 router.

The attack flow typically involves:

1. The attacker identifies a vulnerable Tenda W12 router on the network
2. A specially crafted HTTP request is sent to the web management interface targeting the cgiWifiRadioSet endpoint
3. The oversized input overflows the stack buffer in the vulnerable function
4. Memory corruption occurs, potentially allowing the attacker to control program execution flow
5. Successful exploitation could result in arbitrary code execution with the privileges of the httpd process

Technical details about the vulnerability mechanism can be found in the GitHub Issue Report and VulDB #304982.

Detection Methods for CVE-2025-3693

Indicators of Compromise

• Unexpected HTTP requests to the Tenda W12 web management interface containing unusually long parameter values
• Abnormal router behavior including unexpected reboots, configuration changes, or network anomalies
• Suspicious outbound connections from the router to unknown external IP addresses
• Modified firmware or configuration files on the affected device

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests with abnormally large payloads targeting Tenda router management interfaces
• Monitor for patterns consistent with buffer overflow attempts, such as long strings containing repeated characters or NOP sleds
• Deploy SentinelOne Singularity for network visibility to detect lateral movement originating from compromised IoT devices
• Review router access logs for unusual authentication patterns or repeated requests to configuration endpoints

Monitoring Recommendations

• Establish baseline network behavior for IoT devices and alert on deviations
• Implement network segmentation to isolate vulnerable IoT devices from critical infrastructure
• Enable logging on network firewalls to capture traffic destined for router management ports
• Configure SIEM rules to correlate multiple indicators that may suggest exploitation attempts

How to Mitigate CVE-2025-3693

Immediate Actions Required

• Restrict access to the Tenda W12 web management interface to trusted networks only
• Disable remote management features if not required for business operations
• Place affected devices behind a properly configured firewall with strict access controls
• Monitor the Tenda Website for firmware updates addressing this vulnerability

Patch Information

As of the last modification date, no official patch has been released by Tenda for this vulnerability. Organizations should monitor official Tenda security advisories and vendor communications for updates. The exploit has been publicly disclosed, making it essential to implement compensating controls until a patch becomes available.

For tracking purposes, additional technical details are available through VulDB CTI ID #304982 and VulDB Submission #553526.

Workarounds

• Disable the web management interface entirely and manage the device through console access only if possible
• Implement network-level access control lists (ACLs) to restrict which IP addresses can reach the router's management interface
• Consider replacing vulnerable devices with alternative hardware until a patch is available
• Deploy a Web Application Firewall (WAF) in front of the management interface to filter malicious requests

# Example network ACL configuration to restrict management access
# Limit access to router management interface (example for upstream firewall)
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP