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A recently disclosed vulnerability, CVE-2025-24070, has made headlines for its impact on Microsoft’s ASP.NET Core and Visual Studio. This flaw leaves applications open to weak authentication, enabling an unauthorized attacker to escalate privileges over a network. In this article, we’ll break down what went wrong, showcase some sample code, and walk you through how the exploit works—using easy-to-understand terms with links to further reading.

What is CVE-2025-24070?

CVE-2025-24070 exposes a weakness in the way ASP.NET Core applications—especially those launched or debugged with Visual Studio—handle session authentication. Attackers can spoof authentication tokens or hijack sessions, letting them pretend to be legitimate users (sometimes even admins). This is especially dangerous in corporate environments where sensitive operations are often controlled by web apps.

References

- Microsoft Security Advisory for CVE-2025-24070 (official)
- NVD Entry for CVE-2025-24070

How Does the Vulnerability Work?

The vulnerability occurs because of improper validation of authentication cookies or tokens when an application is started using the default profiles in Visual Studio. Authentication middleware sometimes trusts insecure data, which a remote attacker can easily reproduce.

For developers, the common culprit is careless configuration of authentication in Startup.cs (or in newer .NET, Program.cs). Here’s a faulty example:

// Startup.cs - Weak authentication scheme
services.AddAuthentication("Cookies")
    .AddCookie(options => {
        options.Cookie.HttpOnly = false; // DANGEROUS: Cookie accessible by JavaScript
        options.Cookie.SecurePolicy = CookieSecurePolicy.None; // DANGEROUS: Allows non-HTTPS
        options.Events.OnValidatePrincipal = null; // No validation event
    });

How Can Attackers Exploit This?

Imagine you’re running an ASP.NET Core web app using Visual Studio’s default debug profile (usually with launchSettings.json). By default, this might not enforce HTTPS, or might set up weak authentication out of convenience.

Here’s how a typical attack unfolds

1. Attacker finds a weak session cookie: Since the cookie is not HttpOnly or Secure, they can use a simple XSS payload or sniff traffic on the network.
2. Attacker crafts their own authentication cookie: Because there’s no strict validation, the app will accept this cookie as legit.
3. Privilege escalation: The attacker can tamper with the payload of the cookie to impersonate an admin user.

Here’s a simple proof-of-concept in Python (using requests)

import requests

url = "http://vulnerable-app.local/Admin";
# Forged cookie granting "admin" privilege
cookies = {'.AspNetCore.Cookies': 'forgedadminpayload'} 

r = requests.get(url, cookies=cookies)
if 'Admin Panel' in r.text:
    print("Privilege escalation successful!")
else:
    print("Exploit failed.")

Exploit in Action: Real-World Example

Attackers scan for .NET apps running on default ports (often 500/5001 during dev/debug). If the app allows setting or reusing weak cookies, they drop a malicious payload (via phishing, XSS, or direct traffic interception). Once in, they can:

First, check and apply Microsoft’s patches

- Microsoft Update Catalog for CVE-2025-24070

Always Use Secure Cookies:

options.Cookie.HttpOnly = true;
options.Cookie.SecurePolicy = CookieSecurePolicy.Always;

Validate Principals:

options.Events.OnValidatePrincipal = context => {
    // Check for revoked tokens, check user claims, etc.
    // If invalid:
    // context.RejectPrincipal();
    return Task.CompletedTask;
};

Final Take

CVE-2025-24070 is a serious wakeup call for all ASP.NET Core and Visual Studio users: never trust default authentication settings, and always review how dev tools configure your app. Weak cookies or poor token validation can open doors to network-wide privilege escalation.

Check out these resources for more details

- ASP.NET Core Authentication Docs
- OWASP: Authentication Cheat Sheet

Timeline

Published on: 03/11/2025 17:16:29 UTC
Last modified on: 04/03/2025 21:14:57 UTC