CVE-2018-7536: Django - Catastrophic Backtracking Vulnerability in urlize() Function

Background

Django is a popular Python web framework that provides a set of tools and libraries for building web applications. It includes various features such as an ORM, template engine, and authentication system. The urlize() function in Django is used to implement the urlize and urlizetrunc template filters, which automatically convert URLs in text into clickable links. However, versions of Django prior to 2.0.3, 1.11.11, and 1.8.19 are vulnerable to a catastrophic backtracking vulnerability in the urlize() function.

Vulnerability Detail

The urlize() function in Django is susceptible to catastrophic backtracking due to two regular expressions (one in Django 1.8.x) that evaluate certain inputs very slowly. This vulnerability allows an attacker to craft malicious input that can cause the function to consume excessive CPU resources, leading to denial of service (DoS) attacks. The urlize() function is commonly used in Django templates, making it a potential target for exploitation. The vulnerability was assigned CVE-2018-7536 and has been documented in the PyPI advisory database.

pip install --upgrade "django==6.1.2"

Workaround

If upgrading Django is not immediately feasible, a temporary workaround is to avoid using the urlize and urlizetrunc template filters in Django templates. Instead, developers can manually sanitize and convert URLs in their code to mitigate the risk of exploitation. Here's an example of how to manually sanitize and convert URLs using the Django URLValidator:

from django.core.validators import URLValidator
from django.core.exceptions import ValidationError

def sanitize_and_convert_url(url):
    validator = URLValidator()
    try:
        validator(url)
        return '<a href="' + url + '">' + url + '</a>'
    except ValidationError:
        return url

This code snippet demonstrates a basic approach to sanitize and convert URLs, but it may need to be adapted based on specific application requirements.

Conclusion

The catastrophic backtracking vulnerability in the urlize() function of Django versions prior to 2.0.3, 1.11.11, and 1.8.19 can be mitigated by upgrading to the fixed versions. It is crucial to promptly address this vulnerability to prevent potential denial of service attacks and ensure the security and stability of Django applications. For further assistance or support in vulnerability remediation, please contact DevNack.com.

See every vulnerability recorded for django →

FAQ