Executive Summary

This vulnerability is a buffer overflow flaw found in the Tenda A18 Pro router firmware version 02.03.02.28, specifically in the setSchedWifi function of the /goform/openSchedWifi endpoint.

The function processes Wi-Fi scheduling parameters schedStartTime and schedEndTime, copying them into a fixed-size buffer of 25 bytes using the unsafe strcpy function without checking the length of the input.

Because there is no length validation, an attacker can supply an excessively long schedStartTime string that overflows the allocated buffer, causing a heap buffer overflow.

This flaw can be exploited remotely by sending specially crafted requests to the router.

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Impact Analysis

The vulnerability can lead to several serious impacts:

• Denial of Service (DoS): Memory corruption caused by the overflow can crash the HTTP daemon process, making the device management interface unavailable.
• Remote Code Execution (RCE): An attacker may exploit the overflow to hijack the control flow and execute arbitrary code on the device.

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability can be detected by monitoring or testing the `/goform/openSchedWifi` endpoint on Tenda A18 Pro routers running firmware version V02.03.02.28. Specifically, sending crafted POST requests with oversized `schedStartTime` parameters can trigger the buffer overflow.'}, {'type': 'paragraph', 'content': 'A practical detection method involves sending a POST request with an excessively long `schedStartTime` parameter to see if the device crashes or behaves abnormally, indicating the presence of the vulnerability.'}, {'type': 'list_item', 'content': 'Use a command-line tool like curl to send a test POST request: curl -X POST http://<router-ip>/goform/openSchedWifi -d "schedStartTime=$(python3 -c \'print("1500"*10000)\')&schedEndTime=0000"'}, {'type': 'paragraph', 'content': 'If the device crashes or the HTTP daemon becomes unavailable after this request, it is likely vulnerable.'}] [1]

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Mitigation Strategies

Immediate mitigation steps include restricting access to the vulnerable endpoint and avoiding sending or accepting Wi-Fi schedule configuration inputs from untrusted sources.

If possible, update the firmware to a version where the vulnerability is fixed by replacing unsafe `strcpy` calls with safer alternatives like `strncpy` and implementing strict input validation.

• Block or filter incoming requests to `/goform/openSchedWifi` from untrusted networks.
• Disable remote management features on the router to reduce exposure.
• Monitor the device for crashes or abnormal behavior indicating exploitation attempts.

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