CVE-2011-4138 in Django
Summary
by MITRE
The verify_exists functionality in the URLField implementation in Django before 1.2.7 and 1.3.x before 1.3.1 originally tests a URL s validity through a HEAD request, but then uses a GET request for the new target URL in the case of a redirect, which might allow remote attackers to trigger arbitrary GET requests with an unintended source IP address via a crafted Location header.
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Analysis
by VulDB Data Team • 11/24/2021
The vulnerability CVE-2011-4138 represents a significant security flaw in Django's URLField implementation that existed in versions prior to 1.2.7 and 1.3.1. This issue specifically affects the verify_exists functionality which is designed to validate URL addresses by checking their existence. The vulnerability stems from the inconsistent handling of HTTP requests during URL validation, creating a potential attack vector that can be exploited by remote adversaries to manipulate network traffic patterns.
The technical flaw manifests in the URL validation process where Django initially performs a HEAD request to test URL validity, but when a redirect occurs, it switches to using a GET request for the new target URL. This behavior creates a scenario where malicious actors can craft a Location header in a redirect response that causes the application to make unintended GET requests. The critical aspect of this vulnerability is that these requests are made from the server's IP address rather than from the attacker's source, potentially allowing attackers to bypass certain network restrictions or access resources that would normally be protected from external access.
This vulnerability operates under the principles of server-side request forgery and can be classified under CWE-918, which deals with server-side request forgery vulnerabilities. The attack mechanism aligns with techniques described in the MITRE ATT&CK framework under T1190 for Proxying and T1071.1003 for Application Layer Protocol: DNS, where attackers exploit the application's handling of network requests to achieve unauthorized access. The flaw essentially allows attackers to use the application server as a proxy for making GET requests to arbitrary destinations, potentially exposing internal network resources or bypassing access controls.
The operational impact of this vulnerability is substantial as it can enable attackers to perform unauthorized network reconnaissance, access internal services, or exploit vulnerable systems that are not directly exposed to the internet. An attacker could potentially use this vulnerability to probe internal networks, access restricted resources, or even exploit vulnerabilities in systems that are normally protected by firewalls or other network security controls. The unintended source IP address characteristic means that security systems monitoring network traffic might incorrectly attribute the malicious requests to the application server rather than to the actual attacker.
Organizations using affected Django versions should immediately upgrade to patched releases to mitigate this vulnerability. The recommended mitigation strategy involves implementing proper input validation and sanitization, avoiding the use of the verify_exists functionality in production environments, and configuring proper network access controls to limit what internal resources can be accessed through the application server. Additionally, monitoring network traffic for unusual GET requests originating from the application server can help detect exploitation attempts. Security teams should also consider implementing rate limiting and request validation mechanisms to prevent abuse of URL validation features and ensure that the application properly handles HTTP redirects and location headers.