CVE-2024-51417 - Remote Access Exploit in System.Linq.Dynamic.Core Before 1.6.—What Developers Should Know

System.Linq.Dynamic.Core is a widely-used .NET library that lets you build LINQ queries dynamically. This flexibility is great for developers, but sometimes, it can open doors for attackers if security isn’t tight. The security issue identified as CVE-2024-51417 is a perfect example of this risk. In this post, we’ll unpack what this vulnerability means, show you how an exploit might work, and explain how to protect your apps.

What Is CVE-2024-51417?

In System.Linq.Dynamic.Core versions before 1.6., there’s a vulnerability that lets users create dynamic queries which access certain .NET properties or fields via reflection. Basically, someone could use this to reach into types and even static fields that should be off-limits—like getting environmental variables, secret keys, or other sensitive parts of your application.

How Does the Exploit Work?

When you let users pass in their own queries (think: user-generated filters or sorts), Dynamic LINQ will parse these strings and run them as C# expressions. If the library isn’t strict about what’s allowed, attackers can get creative.

Let’s see a simple code setup that might be vulnerable if you’re using a version before 1.6.

using System.Linq.Dynamic.Core;
using System.Linq;

var myData = Enumerable.Range(1, 10).AsQueryable();
string userQuery = "System.Environment.MachineName"; // User-supplied

// This line will execute the user's query dynamically!
var result = myData.Select(userQuery).ToList();

Before 1.6., this dangerous query runs and leaks your machine name! Worse still, you could potentially access even deeper parts of the .NET API:

// Grab the current process's privileged info
string evilQuery = "System.Diagnostics.Process.GetCurrentProcess().MainModule.FileName";

var stolenInfo = myData.Select(evilQuery).ToList();

Output would be the file path to the executable — definitely something you don’t want to hand out.

What Makes This Exploit Dangerous?

- Attackers don’t need direct server access. If your app lets users submit dynamic queries, an attacker just sends a carefully-crafted string.

How To Fix

Update immediately to at least version 1.6. of System.Linq.Dynamic.Core. In this release, the maintainers tightened up what tokens and expressions can be parsed, shutting out this attack vector.

dotnet add package System.Linq.Dynamic.Core --version 1.6.

Or, if using NuGet Package Manager

Update-Package System.Linq.Dynamic.Core

Extra: How the Patch Works

The patched version blocks access to sensitive types, especially reflection, static fields, and other potentially dangerous APIs. Any attempts to reference things like System.Reflection or static properties from untrusted input will now throw an exception.

Sanitize all user queries to whitelist only known-safe fields and properties.

- Reject any input that contains “System.”, “Reflection”, or class/property/field names you don’t intend to expose.

Here’s a simple whitelist approach

string[] allowedFields = { "Id", "Name", "CreatedDate" };

if (!allowedFields.Contains(userQuery))
{
    throw new Exception("Invalid query field!");
}

References

- Original Advisory by System.Linq.Dynamic.Core
- NVD Record for CVE-2024-51417
- System.Linq.Dynamic.Core GitHub Repository

In Summary

CVE-2024-51417 is a serious risk for any .NET application letting users write or submit their own dynamic LINQ strings. Attackers can use this bug to access deep internals of your running server, leaking sensitive data or even controlling aspects of your app. Don’t wait—inspect your code, upgrade your dependencies, and lock down how and where users can craft queries.

Questions? Want more real-world .NET exploit walk-throughs? Drop a comment below!

Timeline

Published on: 01/21/2025 19:15:10 UTC
Last modified on: 02/04/2025 16:15:38 UTC