Executive Summary

This vulnerability is a critical stack-based buffer overflow found in the Tenda RX3 router firmware version 16.03.13.11, specifically in the /goform/openSchedWifi endpoint. It arises from unsafe handling of user-supplied parameters schedStartTime and schedEndTime, which are copied into a fixed-size buffer without proper length validation. This unsafe copying using the strcpy function allows an attacker to provide oversized input strings that overflow the buffer, causing memory corruption.

The root cause is the lack of bounds checking during the copying of these scheduling time parameters, leading to heap or stack memory corruption. This flaw can be exploited remotely without local access, making it highly accessible to attackers.

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Impact Analysis

Exploitation of this vulnerability can lead to severe impacts including Denial of Service (DoS) and Remote Code Execution (RCE).

• Denial of Service (DoS): Memory corruption caused by the buffer overflow can crash the HTTP daemon process, disabling the device management interface and rendering the router unusable.
• Remote Code Execution (RCE): Carefully crafted inputs can hijack the control flow of the device, allowing an attacker to execute arbitrary code remotely.

Because the exploit is publicly available and the attack can be initiated remotely without authentication, the risk of compromise is high.

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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 the Tenda RX3 router firmware version V16.03.13.11 for abnormal behavior when sending manipulated parameters `schedStartTime` and `schedEndTime`.'}, {'type': 'paragraph', 'content': 'A proof-of-concept exploit involves sending an HTTP POST request with an excessively long `schedStartTime` parameter to trigger the buffer overflow and cause the device to crash or become unresponsive.'}, {'type': 'paragraph', 'content': "Suggested detection commands include using tools like curl or custom scripts to send oversized strings to the vulnerable endpoint and observe the device's response or stability."}, {'type': 'list_item', 'content': 'Example curl command to test the vulnerability: curl -X POST http://<router-ip>/goform/openSchedWifi -d "schedStartTime=$(python3 -c \'print("1500"*10000)\')&schedEndTime=0000"'}, {'type': 'paragraph', 'content': 'If the device crashes, becomes unresponsive, or the HTTP daemon process stops, it indicates the presence of the vulnerability.'}] [2]

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Mitigation Strategies

Immediate mitigation steps include avoiding the use of the vulnerable firmware version V16.03.13.11 on Tenda RX3 routers and restricting access to the `/goform/openSchedWifi` endpoint to trusted users only.

Since the vulnerability arises from unsafe handling of input parameters, it is recommended to implement input validation and replace unsafe functions like `strcpy` with safer alternatives such as `strncpy`.

If possible, update the router firmware to a version where this vulnerability is patched or consider replacing the affected device with a more secure alternative.

In the absence of an official patch, network administrators should monitor for exploitation attempts and limit remote access to the device management interface.

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