CVE-2015-2317 in Django
Summary
by MITRE
The utils.http.is_safe_url function in Django before 1.4.20, 1.5.x, 1.6.x before 1.6.11, 1.7.x before 1.7.7, and 1.8.x before 1.8c1 does not properly validate URLs, which allows remote attackers to conduct cross-site scripting (XSS) attacks via a control character in a URL, as demonstrated by a \x08javascript: URL.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 05/01/2022
The vulnerability identified as CVE-2015-2317 represents a critical cross-site scripting flaw in the Django web framework that affects multiple versions prior to specific security patches. This vulnerability resides within the utils.http.is_safe_url function which is responsible for validating URLs to prevent unsafe redirections. The flaw allows remote attackers to bypass URL validation mechanisms and inject malicious content through carefully crafted URLs containing control characters, specifically demonstrating the exploitation potential through javascript: URLs that could execute arbitrary code in victims' browsers.
The technical implementation of this vulnerability stems from insufficient input validation within Django's URL sanitization logic. When the is_safe_url function processes incoming URLs, it fails to properly sanitize control characters that may be present in the URL structure. This inadequate validation allows attackers to inject malicious protocols such as javascript: or data: that would normally be rejected by proper URL validation. The vulnerability specifically exploits the difference between how URLs are parsed and validated, creating a gap where control characters can slip through without proper encoding or sanitization. This type of flaw maps directly to CWE-79, which describes Cross-Site Scripting vulnerabilities, and more specifically to CWE-116, which addresses improper encoding of control characters.
The operational impact of this vulnerability extends beyond simple XSS attacks as it can enable sophisticated phishing campaigns, session hijacking, and data exfiltration attacks. Attackers can craft malicious URLs that appear legitimate to users while redirecting them to harmful destinations. The vulnerability is particularly dangerous because it can be exploited through various attack vectors including email links, social media posts, or even within web applications that use Django's built-in redirect functionality. This creates a significant risk for organizations using affected Django versions, as any application that relies on user-provided URLs for redirection could become a vector for malicious activity. The attack surface is broad since many web applications use redirect mechanisms that depend on Django's URL validation functions, making this vulnerability particularly widespread.
Mitigation strategies for CVE-2015-2317 require immediate application of security patches to upgrade to affected Django versions that contain the necessary fixes. Organizations should prioritize updating their Django installations to versions 1.4.20, 1.6.11, 1.7.7, or 1.8c1 and later, depending on their current version. Additionally, administrators should implement proper URL validation at multiple layers including application-level input sanitization and web application firewalls that can detect and block suspicious URL patterns. The implementation of Content Security Policy headers can provide additional defense-in-depth measures to prevent execution of unauthorized scripts. Security teams should also conduct thorough code reviews to identify any custom URL handling logic that might be vulnerable to similar issues and ensure that all user-provided URL inputs are properly sanitized before being processed or redirected. This vulnerability demonstrates the importance of proper input validation and the potential consequences of insufficient sanitization in web application security.