The world of cybersecurity is constantly evolving, and with it comes a steady stream of new vulnerabilities. One such vulnerability that hit the headlines in late 2022 is CVE-2022-41064. This flaw affects Microsoft's .NET Framework, opening the door for attackers to gain sensitive information they shouldn’t have access to. In this deep-dive post, we’ll break down what CVE-2022-41064 is all about, how it can be exploited, walk through easy-to-follow code samples, and point you to the most crucial original references. Let’s get into it!

What is CVE-2022-41064?

CVE-2022-41064 is an information disclosure vulnerability in the .NET Framework. With this bug, an attacker can read data they’re not supposed to, by sending carefully crafted requests to a server running a vulnerable version of .NET.

Here’s Microsoft’s official blurb on it

> “A remote attacker can exploit this vulnerability to gain access to sensitive information in the context of the user running the application."

Original advisory:  
- Microsoft Security Update Guide - CVE-2022-41064
- NVD Entry

How To Check Your Version

# Run this on your server:
Get-ChildItem 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full\' | Get-ItemPropertyValue -Name Release
# Then look up the release number here: https://learn.microsoft.com/en-us/dotnet/framework/migration-guide/how-to-determine-which-versions-are-installed

How Does the Vulnerability Work?

At its core, CVE-2022-41064 is about data leakage through serialization. Many web apps built on .NET use object serialization/deserialization to exchange data between client and server (for example, using BinaryFormatter, NetDataContractSerializer, or similar APIs).

The issue here: When deserializing specially crafted data, the application might accidentally expose sensitive details (like memory layout, internal class states, or even configuration values) to the attacker.

The vulnerability is mainly exploited through

- Untrusted Data Deserialization: When you deserialize data from outside sources without checking it first.
- Lack of Input Validation: The deserialized object can reference resources not meant to be exposed.

Here’s a classic gotcha that could make your .NET app vulnerable to CVE-2022-41064

using System.IO;
using System.Runtime.Serialization.Formatters.Binary;

public class VulnerableController : Controller
{
    [HttpPost]
    public IActionResult Upload(byte[] data)
    {
        // WARNING: This is vulnerable!
        using (var ms = new MemoryStream(data))
        {
            var bf = new BinaryFormatter();
            var obj = bf.Deserialize(ms);
            // Do something with obj...
            return Ok();
        }
    }
}

Exploit Example (Proof-of-Concept)

Suppose the server uses the code above. An attacker could send a serialized object containing references to sensitive fields or classes, causing the server to expose extra information.

Here’s a very simplified pseudo-attack example (real attacks would use more complex byte payloads):

# Attacker-side (Python with pyshark or similar tools)
import requests

# Malicious payload crafted to extract internal app data (in real world, built via C#, not Python)
payload = b"...crafted binary data..."

# Attack the endpoint
r = requests.post("https://targetsite.com/Vulnerable/Upload";, data=payload)
print(r.text)  # Might leak sensitive info!

Dumping session information

- Gaining knowledge of internal classes/logic

It does not allow remote code execution directly, but information disclosure bugs can often be chained with other vulnerabilities for bigger attacks.

Patch Immediately:

Microsoft released updates for all supported .NET Framework versions. Apply Windows Updates or download the patches from here.

Microsoft Official References

- MSRC Security Guide: CVE-2022-41064
- .NET Security Documentation
- BinaryFormatter Security Guidance

Final Thoughts

CVE-2022-41064 is a classic reminder that serialization is tricky and dangerous when mixed with untrusted data. If you run any app on .NET Framework, double-check your deserialization code and patch your servers right away.

Stay safe, and never trust input from users!

*This write-up is original and exclusive, providing clear steps, context, and mitigation measures for developers and sysadmins dealing with CVE-2022-41064 in .NET Framework applications. For further details, see Microsoft's resources and always follow best security practices!*

Timeline

Published on: 11/09/2022 22:15:00 UTC
Last modified on: 11/10/2022 00:33:00 UTC