Executive Summary

[{'type': 'paragraph', 'content': 'CVE-2026-2186 is a critical stack-based buffer overflow vulnerability found in the Tenda RX3 router firmware version 16.03.13.11. The flaw exists in the function fromSetIpMacBind within the file /goform/SetIpMacBind, which processes the "list" parameter containing IP-MAC binding rules.'}, {'type': 'paragraph', 'content': 'The vulnerability arises because the function uses the unsafe strcpy function to copy the input string into a fixed-size 128-byte stack buffer without validating the input length. This allows an attacker to overflow the buffer and overwrite the stack frame.'}, {'type': 'paragraph', 'content': 'Additionally, the input is parsed using _isoc99_sscanf, and the function calls set_device_name, which uses unsafe sprintf calls to write into a 256-byte buffer without bounds checking, creating further opportunities for stack corruption.'}, {'type': 'paragraph', 'content': 'An attacker can exploit this remotely by sending a specially crafted "list" parameter to the router\'s /goform/SetIpMacBind endpoint, potentially causing a buffer overflow.'}] [1, 2, 3]

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Impact Analysis

[{'type': 'paragraph', 'content': 'This vulnerability can have severe impacts including:'}, {'type': 'list_item', 'content': 'Remote Code Execution (RCE): An attacker can exploit the buffer overflow to overwrite the saved return address and execute arbitrary code with root privileges on the router.'}, {'type': 'list_item', 'content': "Denial of Service (DoS): Sending malformed or oversized input can crash the router's HTTP daemon, disabling the web management interface and potentially disrupting network connectivity."}, {'type': 'list_item', 'content': 'Compromise of Confidentiality, Integrity, and Availability: Since the router can be fully controlled by an attacker, sensitive network traffic and device configurations can be exposed or altered.'}] [1, 2, 3]

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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 sending a specially crafted HTTP POST request to the endpoint /goform/SetIpMacBind with an excessively large or malformed "list" parameter. For example, sending a very long string (e.g., 10,000 \'A\'s) in the "list" parameter can trigger the stack-based buffer overflow and cause the router\'s web management interface to crash.'}, {'type': 'paragraph', 'content': 'A proof-of-concept Python script exists that demonstrates this detection method by sending such a request to the vulnerable router firmware version V16.03.13.11.'}, {'type': 'list_item', 'content': 'Use curl or similar tools to send a POST request with a large "list" parameter to http://<router-ip>/goform/SetIpMacBind, for example:'}, {'type': 'list_item', 'content': 'curl -X POST -d "list=$(python3 -c \'print("A"*10000)\')" http://<router-ip>/goform/SetIpMacBind'}, {'type': 'paragraph', 'content': 'If the router crashes, becomes unresponsive, or the web interface stops working after this request, it indicates the presence of the vulnerability.'}] [1]

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Mitigation Strategies

[{'type': 'paragraph', 'content': "Immediate mitigation steps include avoiding exposure of the router's web management interface to untrusted networks, especially the internet, to prevent remote exploitation."}, {'type': 'paragraph', 'content': 'Since no vendor patch or fix is currently available, it is recommended to replace the affected product with an alternative device that is not vulnerable.'}, {'type': 'paragraph', 'content': 'Network administrators should also monitor for unusual HTTP POST requests to the /goform/SetIpMacBind endpoint containing abnormally large or malformed "list" parameters and block such traffic if possible.'}, {'type': 'paragraph', 'content': 'Long term, remediation involves applying patches that replace unsafe functions like strcpy with safer alternatives such as strncpy, enforce strict input length validation, and use bounds-checked functions like snprintf in the affected firmware.'}] [1, 3]

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