CVE-2013-6044 in Django
Summary
by MITRE
The is_safe_url function in utils/http.py in Django 1.4.x before 1.4.6, 1.5.x before 1.5.2, and 1.6 before beta 2 treats a URL s scheme as safe even if it is not HTTP or HTTPS, which might introduce cross-site scripting (XSS) or other vulnerabilities into Django applications that use this function, as demonstrated by "the login view in django.contrib.auth.views" and the javascript: scheme.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 01/08/2022
The vulnerability identified as CVE-2013-6044 represents a critical security flaw in the Django web framework's URL validation mechanism. This issue affects versions 1.4.x prior to 1.4.6, 1.5.x prior to 1.5.2, and versions before beta 2 of 1.6, where the is_safe_url function fails to properly validate URL schemes beyond the standard http and https protocols. The flaw stems from the function's overly permissive approach to scheme validation, which allows potentially malicious schemes such as javascript: to be treated as safe, thereby creating pathways for cross-site scripting attacks and other security vulnerabilities within Django applications.
The technical implementation of this vulnerability lies in the flawed logic of the is_safe_url function within Django's utils/http.py module. When processing URLs, the function incorrectly assumes that any URL scheme, regardless of its nature, should be considered safe if it matches certain predefined criteria. This oversight specifically impacts the javascript: scheme and other non-standard schemes that could be exploited to inject malicious code into web applications. The vulnerability manifests when Django applications utilize this function for redirect validation, particularly in authentication flows where users are redirected after login operations. The login view in django.contrib.auth.views serves as a prime example of how this flaw can be exploited, as it relies on the is_safe_url function to validate redirect URLs.
The operational impact of CVE-2013-6044 extends beyond simple XSS attacks, creating potential vectors for more sophisticated exploitation techniques that align with ATT&CK framework tactics such as T1059.007 for Command and Scripting Interpreter and T1566 for Phishing. Applications using Django's authentication system become vulnerable to attackers who can craft malicious URLs with javascript: schemes to redirect users to harmful content. This vulnerability is particularly dangerous because it operates at the framework level, affecting all Django applications that depend on the vulnerable function for URL validation. The flaw essentially allows an attacker to bypass security controls designed to prevent redirection to external domains, potentially leading to session hijacking, credential theft, or the execution of arbitrary JavaScript code within the context of authenticated user sessions.
This vulnerability maps directly to CWE-601, which describes URL Redirector Abuse, and represents a classic case of insufficient input validation in web applications. The flaw demonstrates how seemingly innocuous security functions can become attack vectors when they fail to properly validate user input. Organizations using affected Django versions face significant risk of compromise, as the vulnerability can be exploited without requiring special privileges or advanced technical knowledge. The impact is particularly severe for applications that rely heavily on user redirects, such as single sign-on implementations, OAuth flows, and other authentication mechanisms that depend on redirect validation.
The recommended mitigation strategy involves upgrading to Django versions 1.4.6, 1.5.2, or the corresponding beta 2 release for 1.6, which contain the patched is_safe_url function. Security teams should also implement additional defensive measures including explicit URL scheme validation in custom applications, input sanitization for redirect parameters, and monitoring for suspicious redirect patterns. Organizations should conduct comprehensive vulnerability assessments to identify any custom implementations that might be affected by similar logic flaws, and consider implementing web application firewalls to detect and block suspicious URL patterns. The fix implemented by Django developers specifically addresses the scheme validation logic to ensure that only http and https schemes are considered safe, thereby preventing the exploitation of the javascript: and other potentially dangerous schemes.