Executive Summary

This vulnerability exists in the Tenda A18 Pro router firmware version 02.03.02.28, specifically in the MAC Filtering Configuration Endpoint at /goform/setMacFilterCfg within the function sub_423B50.

The issue arises when the function processes the deviceList parameter, which contains MAC filter rules. It parses this parameter line by line and uses the unsafe strcpy function to copy parts of the input into a fixed-size buffer without checking the length.

Because there is no bounds checking, an attacker can supply an excessively long string that overflows the stack buffer, potentially overwriting the saved return address on the stack.

This stack-based buffer overflow can be triggered remotely by sending a specially crafted request to the vulnerable endpoint.

Useful 0 Not Useful 0

Impact Analysis

[{'type': 'paragraph', 'content': "Exploiting this vulnerability can lead to a denial of service (DoS) by crashing the router's service handling the MAC filter configuration."}, {'type': 'paragraph', 'content': 'More critically, because the overflow overwrites the stack return address, an attacker may be able to execute arbitrary code remotely on the device, potentially gaining control over the router.'}] [1]

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 unusual POST requests to the endpoint `/goform/setMacFilterCfg` that include an excessively long `deviceList` parameter containing carriage return (`\\r`) delimiters.'}, {'type': 'paragraph', 'content': 'A practical detection method is to observe if the service crashes or becomes unresponsive after receiving such requests, which indicates a potential buffer overflow exploitation attempt.'}, {'type': 'paragraph', 'content': 'You can use network monitoring tools or packet capture utilities like tcpdump or Wireshark to filter HTTP POST requests to `/goform/setMacFilterCfg` and inspect the `deviceList` parameter length.'}, {'type': 'paragraph', 'content': 'Example command to capture relevant HTTP POST requests on the network interface eth0:'}, {'type': 'list_item', 'content': "tcpdump -i eth0 -A 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep --line-buffered 'POST /goform/setMacFilterCfg'"}, {'type': 'paragraph', 'content': 'Additionally, a Python script using the requests library can be used to send crafted payloads to test if the service crashes, indicating vulnerability.'}] [1]

Useful 0 Not Useful 0

Mitigation Strategies

Immediate mitigation steps include restricting access to the vulnerable endpoint `/goform/setMacFilterCfg` by implementing network-level controls such as firewall rules to block unauthorized or external access.

Limit access to trusted users or management networks only, and monitor for suspicious POST requests containing large or malformed `deviceList` parameters.

If possible, disable the MAC Filtering Configuration feature temporarily until a firmware update or patch is available.

Applying vendor-provided firmware updates or patches that fix the buffer overflow vulnerability is the most effective long-term mitigation.

Useful 0 Not Useful 0