In recent times, a newly discovered security vulnerability in the widely used web framework Django has caused significant concern within the developer community. This vulnerability, designated as CVE-2023-43665, affects the popular Django versions 3.2 (before 3.2.22), 4.1 (before 4.1.12), and 4.2 (before 4.2.6). It centers around the 'django.utils.text.Truncator' class and its 'chars()' and 'words()' methods, which, when used with the 'html=True' flag, can potentially lead to a denial of service (DoS) attack through specific input containing long, possibly malformed pieces of HTML content.

To better understand this issue, it's essential to note that this vulnerability results from an incomplete fix to a previous security threat, CVE-2019-14232. In this long read, we will delve into what this vulnerability means for Django users, including the code snippets, original references, and exploit details, all explained in simple American language.

Code Snippets

To demonstrate this vulnerability, consider the following example of a typical usage scenario of the 'chars()' and 'words()' methods with 'html=True'.

from django.utils.text import Truncator

malformed_html = '''
<!doctype HTML PUBLIC "-//W3C//DTD HTML 4. Transitional//EN">

# Potentially long and malformed HTML content


truncated_chars = Truncator(malformed_html, html=True).chars(50)
truncated_words = Truncator(malformed_html, html=True).words(50)

By supplying a very long and potentially malformed HTML input to the 'Truncator' class and invoking the 'chars()' and 'words()' methods with 'html=True', an attacker can cause a significant slowdown or exhaustion of resources, resulting in a DoS attack.

Several resources detail this vulnerability, including the official Django Project security advisory and GitHub pull requests that aim to provide a fix for the issue. Here are a few essential links where you can delve deeper into understanding and resolving the problem:

1. Django Project Security Advisory post on CVE-2023-43665: Django Security Advisory
2. GitHub Pull Request for Django 3.2: #15494
3. GitHub Pull Request for Django 4.1: #15495
4. GitHub Pull Request for Django 4.2: #15496

Exploit Details

The exploit of CVE-2023-43665 involves providing a string of long, potentially malformed HTML content as input to the 'Truncator.chars()' or 'Truncator.words()' methods with 'html=True'. This input would require a considerable amount of processing time and resources, causing performance degradation or unavailability of the web application, effectively resulting in a denial of service attack. Since these methods are used to implement the 'truncatechars_html' and 'truncatewords_html' template filters, these filters are also vulnerable.

It is crucial to rectify the vulnerability as soon as possible to prevent potential exploitation. To protect your Django application from this vulnerability, update your Django installation to the latest respective patch release (Django 3.2.22, 4.1.12, or 4.2.6).

In conclusion, CVE-2023-43665 is a serious security vulnerability affecting many Django installations, and the root cause lies in an incomplete fix for CVE-2019-14232. It is essential for developers and system administrators to familiarize themselves with this issue, update their installations accordingly, and keep an eye on future security updates from the Django Project.


Published on: 11/03/2023 05:15:30 UTC
Last modified on: 12/21/2023 22:15:14 UTC