Stack-Based Buffer Overflow in Tenda JD12L Router

Executive Summary

CVE-2026-13519 is a buffer overflow vulnerability found in the Tenda JD12L router firmware version 16.03.53.23. It occurs in the function fromNatStaticSetting within the /goform/NatStaticSetting endpoint. The vulnerability arises because the function uses the unsafe sprintf function to process a user-controlled parameter called page without properly checking its length.

Since the buffer used is fixed at 256 bytes, providing input larger than this size can overwrite adjacent memory on the stack. This can lead to memory corruption, application crashes, or even allow an attacker to execute arbitrary code remotely.

The exploit can be triggered remotely without authentication, making it particularly dangerous. The vulnerability has been publicly disclosed and a proof-of-concept exploit exists.

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Impact Analysis

This vulnerability can have serious impacts including denial of service, information leakage, and potentially full device compromise.

• Denial of Service (DoS) by causing application crashes.
• Information leakage due to memory corruption.
• Remote code execution leading to full control over the affected device.

Since the exploit does not require authentication, attackers can remotely exploit this vulnerability to disrupt network operations or gain unauthorized access to the device.

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Detection Guidance

This vulnerability can be detected by monitoring network traffic for POST requests to the /goform/NatStaticSetting endpoint containing an unusually large or oversized 'page' parameter.

A practical detection method is to use network analysis tools like tcpdump or Wireshark to capture and inspect HTTP POST requests targeting this endpoint.

For example, you can use the following tcpdump command to capture relevant traffic:

• tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/goform/NatStaticSetting'

Additionally, inspecting logs or using intrusion detection systems (IDS) to look for POST requests with large payloads or suspicious 'page' parameter values can help identify exploitation attempts.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the vulnerable endpoint and limiting exposure of the affected device to untrusted networks.

Since no patch is currently available from the vendor, it is recommended to implement network-level protections such as firewall rules to block or limit POST requests to /goform/NatStaticSetting.

Other recommended mitigations include applying the principle of least privilege to reduce potential damage and monitoring for suspicious activity targeting this endpoint.

Long-term mitigation involves updating the firmware once a patch is released that replaces unsafe functions like sprintf with safer alternatives and implements strict input validation.

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Compliance Impact

The vulnerability in Tenda JD12L allows remote attackers to cause buffer overflow, potentially leading to denial of service, information leakage, or full device compromise.

Such security weaknesses can impact compliance with standards like GDPR and HIPAA, which require protection of personal and sensitive data against unauthorized access and breaches.

If exploited, this vulnerability could lead to unauthorized disclosure or alteration of data, violating confidentiality and integrity requirements mandated by these regulations.

Therefore, failure to patch or mitigate this vulnerability may result in non-compliance with these common security standards.

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