Stack-Based Buffer Overflow in Tenda F451 httpd Allows Remote Exploit

Executive Summary

CVE-2026-6123 is a stack-based buffer overflow vulnerability found in the Tenda F451 firmware version 1.0.0.7, specifically in the fromAddressNat function of the httpd service.

The vulnerability occurs because the function reads a user-supplied parameter named "entrys" and stores it in a variable that is then passed to the sprintf function without any bounds checking. This lack of validation allows an attacker to overflow the buffer.

An attacker can exploit this remotely by sending a crafted HTTP POST request to the "/goform/addressNat" endpoint with an oversized "entrys" parameter, potentially causing a denial of service or enabling remote code execution.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the vulnerable endpoint "/goform/addressNat" to trusted users only, such as by implementing firewall rules or access control lists.

Additionally, monitoring and blocking suspicious HTTP POST requests with unusually large "entrys" parameters can help prevent exploitation.

If possible, update the firmware of the Tenda F451 device to a version where this vulnerability is patched or contact the vendor for a security update.

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Compliance Impact

The provided information does not specify any direct impact of the CVE-2026-6123 vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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Impact Analysis

This vulnerability can have serious impacts including denial of service (DoS) and remote code execution on the affected device.

An attacker exploiting this flaw can crash the device or take control of it remotely by sending a specially crafted HTTP POST request.

Such impacts can lead to service disruption, unauthorized access, and potential compromise of the network where the device is deployed.

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Detection Guidance

This vulnerability can be detected by monitoring for HTTP POST requests sent to the "/goform/addressNat" endpoint containing an unusually large or oversized "entrys" parameter.

A practical detection method is to capture and analyze network traffic for such requests, especially those with payloads similar to the proof of concept which sends 2048 bytes of the character 'a' in the "entrys" field.

For example, using command-line tools like curl or netcat to simulate or detect such requests can help identify attempts to exploit this vulnerability.

• Use a network packet capture tool (e.g., tcpdump or Wireshark) to filter HTTP POST requests to "/goform/addressNat".
• Example tcpdump command: tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/goform/addressNat'
• Use curl to test the endpoint with a crafted payload: curl -X POST http://<target-ip>/goform/addressNat -d 'entrys=$(python3 -c "print('a'*2048)")'

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