Buffer Overflow in TRENDnet TEW-821DAP Firmware

Executive Summary

This vulnerability is a buffer overflow in the Trendnet TEW-821DAP router firmware version 1.12B01. It occurs in the function sub_41EC14 of the ssi component, specifically when handling the nslookup_target argument. The argument is copied into a buffer of only 2 bytes without size checks. If an attacker sends input longer than 392 bytes via an HTTP POST request to /goform/tools_nslookup, it causes a buffer overflow.

This overflow can overwrite the return address on the stack, potentially allowing an attacker to execute arbitrary code remotely.

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Impact Analysis

The vulnerability allows remote attackers to exploit a buffer overflow, which can lead to arbitrary code execution on the affected device.

This means an attacker could potentially take control of the router, disrupt network operations, intercept or manipulate network traffic, or use the device as a foothold for further attacks within the network.

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Detection Guidance

This vulnerability can be detected by monitoring for HTTP POST requests sent to the endpoint /goform/tools_nslookup, which is the exploit path triggering the buffer overflow.

Specifically, detection involves identifying unusually large or malformed POST requests containing the nslookup_target parameter with payloads exceeding normal size limits (greater than 2 bytes, potentially over 392 bytes).

Network administrators can use packet capture tools like tcpdump or Wireshark to filter and analyze HTTP POST traffic to /goform/tools_nslookup.

• Example tcpdump command to capture relevant traffic: tcpdump -i <interface> -A 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/goform/tools_nslookup'
• Use curl or similar tools to test the endpoint by sending crafted POST requests with varying sizes of nslookup_target to observe abnormal behavior.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the vulnerable endpoint /goform/tools_nslookup to trusted users only, ideally by firewall rules or network segmentation.

Since the affected product (TRENDnet TEW-821DAP 1.12B01) is no longer supported by the vendor, applying official patches is not possible.

As a workaround, disable or block HTTP POST requests to /goform/tools_nslookup to prevent exploitation.

Consider replacing the affected device with a supported model to ensure ongoing security updates.

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