Heap overflow vulnerabilities can cause serious security risks, potentially allowing attackers to execute arbitrary code, crash the application, or leak sensitive information. It's crucial that we keep an eye out for these weaknesses and find ways to fix them. In this article, we'll explore a heap overflow vulnerability found in Tenda AX1803 v1...1's GetParentControlInfo function (CVE-2022-40875).

1. Original CVE report: https://.../vulns/CVE-2022-40875
2. Tenda AX1803 Router: https://.../tenda-ax1803
3. Heap overflow explanation: https://.../heap-overflow-exploitation

Vulnerability Details

The vulnerability was discovered in the GetParentControlInfo function of Tenda AX1803 v1...1. This function is responsible for processing the Parent Control settings' information, which is used for controlling internet access permissions for specific devices/users.

When processing the Parent Control settings, an attacker can send an overly long string that causes a heap overflow in the GetParentControlInfo function. This overflow could potentially lead to a crashed application, leakage of sensitive information, or even arbitrary code execution. For a successful exploit, the attacker would need to trick the target into sending crafted Parent Control data that exploits this specific heap overflow.

Below is a code snippet from the GetParentControlInfo function illustrating the heap overflow vulnerability:

int GetParentControlInfo(...)
{
    ...
    char buffer[200];
    
    // Loop through all Parent Control data
    for (int i = ; i < num_of_parent_controls; ++i)
    {
        ...
        // Vulnerable code: strcpy can overflow the buffer if pc_data is too long
        strcpy(buffer, pc_data);
        ...
    }
}

In the snippet above, the strcpy function is called to copy the pc_data variable to the buffer array. However, there is no check to ensure that pc_data is not longer than the buffer array's size. If an attacker sends a string longer than 200 characters, it would result in a heap overflow, causing the application to exhibit the aforementioned undesirable behaviors.

Exploitation

In order to exploit this vulnerability, an attacker would first need to gain access to the network where the targeted Tenda AX1803 v1...1 router is connected. Once on the same network, the attacker can send a crafted Parent Control information package to exploit the heap overflow vulnerability.

However, this specific exploit would require a thorough understanding of the target network, router setup, and the entire attack surface. The attacker would need to monitor the target network for appropriate opportunities to initiate the attack and craft a payload based on the discovered Parent Control settings.

Mitigation

To mitigate this vulnerability, users should keep their firmware updated and apply any patches released by Tenda. Router manufacturers should also take steps to address such heap overflows by implementing secure coding practices. In this specific case, the use of functions like strncpy with proper bounds checking would help prevent the buffer overflow.

As always, users are encouraged to use strong, unique passwords for their routers and implement robust network security measures, such as utilizing firewalls and network segmentation to protect their assets.

Conclusion

CVE-2022-40875 highlights the importance of secure coding practices and staying vigilant in identifying and patching vulnerabilities like heap overflows. Ensuring that your software (or firmware for routers) is up-to-date can go a long way in keeping your systems secure from threats. Let's work together to make the internet a safer place for everyone.

Timeline

Published on: 10/27/2022 18:15:00 UTC
Last modified on: 10/28/2022 18:40:00 UTC