Stack-Based Buffer Overflow in Tenda JD12L Router Firmware

Executive Summary

CVE-2026-13515 is a critical buffer overflow vulnerability in the Tenda JD12L router firmware version 16.03.53.23. It exists in the function formSetPPTPServer within the /goform/SetPptpServerCfg endpoint. The vulnerability arises because the startIp parameter is parsed without proper bounds checking, allowing an attacker to supply an excessively large input that overwrites stack memory.

This improper parsing can lead to application crashes, memory corruption, or even arbitrary code execution. The attack can be launched remotely and does not require authentication.

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Impact Analysis

Exploitation of this vulnerability can result in denial of service, information leakage, or full device takeover. An attacker can crash the application, corrupt memory, or execute arbitrary code remotely without needing authentication.

This means your device could be rendered unusable, sensitive information could be exposed, or an attacker could gain control over the router, potentially compromising your entire network.

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Detection Guidance

This vulnerability can be detected by monitoring for suspicious POST requests sent to the `/goform/SetPptpServerCfg` endpoint containing an excessively large or malformed `startIp` parameter.

A proof-of-concept exploit involves sending a malformed POST request with an oversized `startIp` parameter, which can cause application crashes or memory corruption.

To detect potential exploitation attempts on your network, you can use network monitoring tools or packet capture utilities like tcpdump or Wireshark to filter HTTP POST requests targeting `/goform/SetPptpServerCfg`.

• Example tcpdump command to capture suspicious traffic: tcpdump -i <interface> -A 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/goform/SetPptpServerCfg'
• Use curl or similar tools to test the endpoint by sending a POST request with an oversized `startIp` parameter to observe if the device crashes or behaves abnormally.

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Mitigation Strategies

Immediate remediation steps include replacing unsafe parsing functions and implementing strict input validation on the `startIp` parameter to prevent buffer overflow.

Apply the principle of least privilege to limit the impact of any potential exploit.

Enable compiler protections such as stack canaries and Address Space Layout Randomization (ASLR) to mitigate exploitation.

If possible, update the firmware of the Tenda JD12L device to a version where this vulnerability is patched.

In the absence of a patch, consider blocking or filtering incoming traffic to the vulnerable endpoint `/goform/SetPptpServerCfg` at the network perimeter to prevent remote exploitation.

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Compliance Impact

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

Such security weaknesses can impact compliance with standards like GDPR and HIPAA because they may lead to unauthorized access or exposure of sensitive personal or health data, violating data protection and privacy requirements.

Organizations using affected devices must address this vulnerability promptly to maintain compliance by ensuring confidentiality, integrity, and availability of data.

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