Executive Summary

[{'type': 'paragraph', 'content': 'CVE-2026-2930 is a stack-based buffer overflow vulnerability found in the Tenda A18 router firmware version 15.13.07.13. It exists in the Httpd Service component, specifically in the function webCgiGetUploadFile within the /cgi-bin/UploadCfg interface.'}, {'type': 'paragraph', 'content': "The vulnerability occurs because the 'boundary' parameter from a multipart/form-data POST request is not properly validated for length before being copied into a fixed-size stack buffer. This improper handling allows an attacker to overflow the buffer on the stack."}, {'type': 'paragraph', 'content': 'Exploiting this flaw can lead to remote code execution or cause a denial of service (DoS) condition on the device. The attack can be performed remotely without requiring local access or physical interaction.'}] [1, 2, 3]

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Impact Analysis

This vulnerability can have serious impacts including remote code execution, which allows an attacker to run arbitrary code on the affected device.

It can also cause a denial of service (DoS), making the router unavailable or unstable.

Because the vulnerability affects confidentiality, integrity, and availability of the device, it can compromise the security and proper functioning of your network.

There are no known mitigations or patches available, so the recommended action is to replace the affected product to avoid risk.

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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 for suspicious HTTP POST requests targeting the '/cgi-bin/UploadCfg' endpoint on Tenda A18 routers running firmware version 15.13.07.13. Specifically, look for requests containing a multipart/form-data POST with a specially crafted 'boundary' parameter that exceeds normal length or contains unusual characters."}, {'type': 'paragraph', 'content': "Network intrusion detection systems (NIDS) or web application firewalls (WAF) can be configured to alert on unusually long or malformed 'boundary' parameters in HTTP POST requests to this endpoint."}, {'type': 'paragraph', 'content': "Example commands to detect such activity might include using tools like tcpdump or tshark to capture and filter HTTP POST requests to '/cgi-bin/UploadCfg':"}, {'type': 'list_item', 'content': "tcpdump -i <interface> -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/cgi-bin/UploadCfg'"}, {'type': 'list_item', 'content': 'tshark -i <interface> -Y \'http.request.method == "POST" and http.request.uri contains "/cgi-bin/UploadCfg"\' -T fields -e http.file_data'}, {'type': 'paragraph', 'content': "Additionally, inspecting logs for abnormal POST requests with large or malformed 'boundary' strings can help identify exploitation attempts."}] [1, 2, 3]

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Mitigation Strategies

[{'type': 'paragraph', 'content': 'Currently, there are no known vendor-provided patches or fixes available for this vulnerability in the Tenda A18 router firmware version 15.13.07.13.'}, {'type': 'paragraph', 'content': 'Immediate mitigation steps include:'}, {'type': 'list_item', 'content': "Disabling remote access to the router's web management interface to prevent exploitation from external networks."}, {'type': 'list_item', 'content': "Restricting access to the '/cgi-bin/UploadCfg' endpoint via firewall rules or access control lists to trusted internal networks only."}, {'type': 'list_item', 'content': 'Monitoring network traffic for suspicious POST requests targeting the vulnerable endpoint and blocking malicious IP addresses.'}, {'type': 'list_item', 'content': 'Considering replacing the affected device with a different model or vendor that is not vulnerable to this issue.'}, {'type': 'paragraph', 'content': 'These steps help reduce the risk of exploitation until an official patch or firmware update is released.'}] [2]

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