OpenVPN is a widely used VPN solution that provides secure and encrypted communication between devices. This long read post discusses a security vulnerability (CVE-2023-7235) found in the OpenVPN GUI installer before version 2.6.9, which did not set the proper access control restrictions to the installation directory of OpenVPN binaries when using a non-standard installation path. This vulnerability could allow an attacker to replace binaries with malicious executables, potentially compromising the user's system.

Description of the Vulnerability

The vulnerability (CVE-2023-7235) is present in the OpenVPN GUI installer before version 2.6.9. When a user installs the OpenVPN software, the installer does not set the proper access control restrictions to the installation directory of OpenVPN binaries, allowing an attacker to manipulate the installed files. This is especially true when a non-standard installation path is used, as there would be even less security in place.

An attacker can exploit this vulnerability by replacing the OpenVPN binaries with malicious executables. When the user runs the OpenVPN software, the malicious executables will be executed, potentially compromising the user's system.

For example, let's assume that a user has installed OpenVPN in a non-standard path, such as "C:\custom-path\openvpn". An attacker can replace the legitimate "openvpn.exe" binary with a malicious file, and when the user tries to initiate a VPN connection, the attacker's payload will be executed.

Code Snippet

A hypothetical sample of malicious code that could be injected in the OpenVPN binary could be a simple backdoor to obtain the user's system information:

#include <iostream>
#include <fstream>
#include <windows.h>
#include <Lmcons.h>

int main()
{
    TCHAR username[UNLEN+1];
    DWORD size = UNLEN+1;

    GetUserName((TCHAR*)username, &size);
    std::ofstream outFile;
    outFile.open("stolen-data.txt", std::ios::out | std::ios::app);
    outFile << "Username: " << username << std::endl;
    outFile.close();
    
    // The actual OpenVPN binary would be run here to avoid suspicion
    return ;
}

Original References

The vulnerability was first disclosed by an independent security researcher and has been assigned the CVE identifier CVE-2023-7235.
- NVD - CVE-2023-7235
- OpenVPN Security Advisory

Exploit Details

To exploit this vulnerability, an attacker would need to have access to the target system, either through physical access or by compromising the system via another vulnerability. Once the attacker gains access, they can replace the OpenVPN binaries with malicious executables in the non-standard installation path.

Users can protect themselves against this vulnerability by following these guidelines

1. Upgrade OpenVPN GUI to version 2.6.9 or later: The vulnerability is fixed in OpenVPN GUI versions 2.6.9 and later. Download and install the latest version of OpenVPN GUI from the official website: OpenVPN Download
2. Use the default installation path: By using the standard installation path, users can ensure that their OpenVPN installation is protected with proper access control restrictions.
3. Limit user privileges on the system: Restricting user privileges can prevent an attacker from executing malicious files.
4. Monitor system files for any unauthorized changes: Regularly scan installed applications and their files for any changes made without user consent.

Conclusion

The CVE-2023-7235 vulnerability in the OpenVPN GUI installer before version 2.6.9 is a serious security issue that can allow an attacker to replace the OpenVPN binaries with arbitrary executables. By upgrading to the latest version of OpenVPN GUI and adhering to the mitigation steps listed above, users can protect themselves from this vulnerability and maintain a secure VPN connection.

Timeline

Published on: 02/21/2024 11:15:07 UTC
Last modified on: 08/26/2024 17:35:02 UTC