CVE-2024-21397: Exploring Microsoft Azure File Sync Elevation of Privilege Vulnerability and Analyzing Exploit Techniques

Microsoft Azure is a key player in cloud computing, offering services ranging from computing to networking to storage. Azure File Sync is one such service, designed to synchronize files across different servers and Azure Files. However, a recent vulnerability (CVE-2024-21397) has put the security of this service into question, leaving organizations exposed to an elevation of privilege threat. In this post, we will break down the nature of the vulnerability, study the exploit code, and discuss the potential impact on organizations.

What is the vulnerability?
The CVE-2024-21397 vulnerability is classified as an elevation of privilege attack, which allows an attacker to execute malicious actions that would normally be restricted by the system. In this instance, the vulnerability lies in the improper handling of the Inter-Process Communication (IPC) mechanism in the Azure File Sync Agent. This could potentially allow a local attacker to impersonate a higher privileged user, and subsequently access sensitive data or execute arbitrary code.

Link to original reference

More details about the vulnerability can be found in the official notification from Microsoft here.

Exploit code snippet

Inside the Azure File Sync Agent subsystem, there is a named pipe used for communication with the monitoring service. When a client application connects to this named pipe and sends a specific type of message, the agent does not properly validate the client's permissions. Below is a high-level representation of the attack:

import ctypes

# Load the Windows API CreateFileA function
CreateFile = ctypes.windll.kernel32.CreateFileA

# Specify the target named pipe
named_pipe = "\\\\.\\pipe\\AzureFileSyncIPC"

# Call the CreateFile function to connect to the named pipe
handle = CreateFile(named_pipe, GENERIC_READ | GENERIC_WRITE, , None, OPEN_EXISTING, , None)

# Check if the connection was successful
if handle == INVALID_HANDLE_VALUE:
    print("Failed to connect to named pipe.")
else:
    print("Connected to named pipe.")

# Craft malicious message and send it to the named pipe
malicious_message = "Some malicious content"
write_response = ctypes.windll.kernel32.WriteFile(handle, malicious_message, len(malicious_message), None, None)

# Close the connection
ctypes.windll.kernel32.CloseHandle(handle)

In the above code snippet, the attacker connects to the named pipe, sends a crafted malicious message, and then closes the connection. Due to improper validation in the agent, this message may convince the system to grant the attacker higher privileges.

Mitigation and prevention

Microsoft has released patches to fix the vulnerability, and organizations are strongly advised to apply the patches at their earliest convenience. Additionally, it is recommended to follow security best practices such as:

1. Implement the principle of least privilege, granting users the minimum level of access necessary to perform their tasks.
2. Regularly audit and update all applications, frameworks, and operating systems to ensure they are protected with the latest security patches.
3. Train employees on security awareness, particularly around recognizing and reporting potential threats or suspicious activity.

Conclusion

The CVE-2024-21397 vulnerability exposes Microsoft Azure File Sync users to an elevation of privilege threat. By exploiting this vulnerability, malicious actors may be able to gain unauthorized access to sensitive data or execute arbitrary code. Organizations relying on Azure services should remain vigilant, apply available security patches, and continuously follow best practices to ensure the safety of their digital assets.

Timeline

Published on: 02/13/2024 18:15:58 UTC
Last modified on: 02/23/2024 17:47:25 UTC