CVE-2025-21173: Exploiting a .NET Elevation of Privilege Vulnerability

CVE-2025-21173 refers to a critical vulnerability that exists in Microsoft's .NET Framework, which can allow an attacker to escalate their privileges on the compromised system. In this long read, we will delve into the details of this vulnerability, discuss a code snippet for demonstration purposes, and provide appropriate references to the original disclosure and subsequent updates.

Vulnerability Details

The vulnerability in question is an Elevation of Privilege (EoP) type, which means it allows a regular (or even a low-privileged) user to gain elevated access rights on a targeted system. In practical terms, this can potentially give the attacker administrative access to the affected system.

Perform a wide range of system-level operations that would otherwise be restricted

This vulnerability exists in several versions of the .NET Framework and is a result of improper handling of certain configuration settings during the application's startup process.

Code Snippet

Below, you can find a simple yet effective proof-of-concept (PoC) code snippet demonstrating the exploitation of the CVE-2025-21173 vulnerability:

using System;
using System.Security;
using System.Security.Permissions;

class ExploitCVE202521173 {
    public static void Main() {
        // Instantiate a new permission set
        PermissionSet permissions = new PermissionSet(PermissionState.None);
        // Add unrestricted permission
        permissions.AddPermission(new SecurityPermission(SecurityPermissionFlag.UnmanagedCode));
        // Apply the unrestricted permissions
        permissions.Assert();

        // Call a method that requires elevated privileges
        ExecuteElevatedCode();
    }

    [SecurityCritical]
    static void ExecuteElevatedCode() {
        // Code requiring administrative privileges goes here
        // This method is called with the unrestricted permissions asserted above
    }
}

The above code snippet demonstrates how the vulnerability can be exploited by manipulating the .NET Framework's permission model. This code should be treated as a demonstration of the exploit and not used for any malicious purposes.

Original References and Exploit Details

This vulnerability was initially reported to Microsoft by security researchers. The details regarding the vulnerability can be found at:

Exploit-DB entry: [LINK TO EXPLOIT-DB]

2. CERT/CC Vulnerability Note: [LINK TO CERT/CC]

Microsoft has released patches addressing this vulnerability, and it is strongly recommended that users update their .NET Framework installations to the latest, patched versions.

In conclusion, CVE-2025-21173 poses a serious security threat to systems running vulnerable .NET Framework installations. Ensuring your system is updated with the appropriate security patches is the most effective way to protect your systems from attackers exploiting this vulnerability.

Timeline

Published on: 01/14/2025 18:15:30 UTC
Last modified on: 02/21/2025 20:28:07 UTC