CVE-2021-40556 Explained : Impact and Mitigation

A stack overflow vulnerability exists in the httpd service in ASUS RT-AX56U Router Version 3.0.0.4.386.44266. This vulnerability allows an attacker to execute commands remotely.

Understanding CVE-2021-40556

This CVE involves a stack overflow vulnerability in the httpd service of ASUS RT-AX56U Router, enabling remote command execution.

What is CVE-2021-40556?

The vulnerability in the httpd service of ASUS RT-AX56U Router Version 3.0.0.4.386.44266 allows users to input 0xFFFF bytes into the stack through the "caupload" input handle function.

The Impact of CVE-2021-40556

The vulnerability allows an attacker to execute commands remotely on the affected router, potentially leading to unauthorized access and control of the device.

Technical Details of CVE-2021-40556

This section provides in-depth technical information about the CVE.

Vulnerability Description

The vulnerability is due to the strcat function in the "caupload" input handle function, enabling the user to overflow the stack with 0xFFFF bytes.

Affected Systems and Versions

Vendor: n/a
Product: n/a
Versions: Version 3.0.0.4.386.44266 (affected)

Exploitation Mechanism

The vulnerability is exploited by inputting a large number of bytes (0xFFFF) into the stack, triggering a stack overflow and allowing malicious command execution.

Mitigation and Prevention

Steps to secure systems and prevent exploitation of the vulnerability.

Immediate Steps to Take

Apply vendor patches promptly.
Implement strong authentication mechanisms.
Monitor network traffic for unusual activity.

Long-Term Security Practices

Regularly update firmware and software.
Conduct security audits and penetration testing.
Educate users on safe computing practices.

Patching and Updates

Check for and install updates from ASUS for the RT-AX56U Router.