Executive Summary

[{'type': 'paragraph', 'content': 'CVE-2026-4535 is a critical vulnerability in the Tenda FH451 router, version 1.0.0.9. It is a stack-based buffer overflow found in the HTTP daemon\'s WrlclientSet function. This function processes a user-supplied parameter named "GO" without validating its length. When an attacker sends a specially crafted HTTP POST request with an excessively long "GO" parameter to the /goform/WrlclientSet endpoint, it causes the buffer to overflow.'}, {'type': 'paragraph', 'content': 'This overflow occurs because the input is copied into a fixed-size stack buffer using the sprintf function without proper length checks, leading to memory corruption.'}, {'type': 'paragraph', 'content': 'Exploitation of this vulnerability can lead to denial of service (DoS) or remote code execution (RCE) on the affected device.'}] [1]

Useful 0 Not Useful 0

Impact Analysis

This vulnerability can have severe impacts on users of the Tenda FH451 router version 1.0.0.9. An attacker can remotely exploit the buffer overflow by sending a crafted HTTP POST request, which may result in:

• Denial of Service (DoS) - causing the router to crash or become unresponsive.
• Remote Code Execution (RCE) - allowing the attacker to execute arbitrary code on the device, potentially taking full control over it.

Such control could lead to interception of network traffic, unauthorized access to the internal network, or further attacks on connected devices.

Useful 0 Not Useful 0

Compliance Impact

I don't know

Useful 0 Not Useful 0

Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability can be detected by monitoring for specially crafted HTTP POST requests sent to the endpoint /goform/WrlclientSet containing an excessively long "GO" parameter.'}, {'type': 'paragraph', 'content': 'A practical detection method is to capture and analyze HTTP traffic to identify POST requests targeting /goform/WrlclientSet with unusually large payloads in the "GO" parameter.'}, {'type': 'paragraph', 'content': 'For example, using command-line tools like curl or wget to send test requests or using network monitoring tools such as tcpdump or Wireshark to filter and inspect HTTP POST requests can help detect attempts to exploit this vulnerability.'}, {'type': 'list_item', 'content': "Use tcpdump to capture HTTP POST requests to /goform/WrlclientSet: tcpdump -i <interface> -A 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/goform/WrlclientSet'"}, {'type': 'list_item', 'content': 'Use curl to test the endpoint with a large GO parameter: curl -X POST http://<target-ip>/goform/WrlclientSet -d \'GO=$(python3 -c "print(\'A\'*1000)")\''}] [1]

Useful 0 Not Useful 0

Mitigation Strategies

[{'type': 'paragraph', 'content': 'Immediate mitigation steps include restricting access to the vulnerable endpoint /goform/WrlclientSet by implementing firewall rules or access control lists to block unauthorized or suspicious HTTP POST requests.'}, {'type': 'paragraph', 'content': 'Additionally, monitoring and filtering HTTP traffic to detect and block requests with abnormally large "GO" parameters can reduce the risk of exploitation.'}, {'type': 'paragraph', 'content': 'If possible, update the firmware of the Tenda FH451 router to a version that patches this vulnerability or apply any vendor-provided security updates.'}, {'type': 'paragraph', 'content': 'Until a patch is available, consider isolating the device from untrusted networks or limiting remote management access.'}] [1]

Useful 0 Not Useful 0