CVE-2017-7233 in Django
Summary
by MITRE
Django 1.10 before 1.10.7, 1.9 before 1.9.13, and 1.8 before 1.8.18 relies on user input in some cases to redirect the user to an "on success" URL. The security check for these redirects (namely ``django.utils.http.is_safe_url()``) considered some numeric URLs "safe" when they shouldn't be, aka an open redirect vulnerability. Also, if a developer relies on ``is_safe_url()`` to provide safe redirect targets and puts such a URL into a link, they could suffer from an XSS attack.
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Analysis
by VulDB Data Team • 11/27/2022
The vulnerability identified as CVE-2017-7233 represents a critical open redirect flaw affecting multiple versions of the Django web framework. This issue stems from improper validation logic within the django.utils.http.is_safe_url() utility function, which is designed to verify whether redirect URLs are safe for use in web applications. The vulnerability affects Django versions 1.10 prior to 1.10.7, 1.9 prior to 1.9.13, and 1.8 prior to 1.8.18, making it a widespread concern across several long-term support releases. The flaw specifically manifests when the function incorrectly classifies certain numeric URLs as safe, creating potential attack vectors for malicious actors to redirect users to unintended destinations.
The technical implementation of this vulnerability lies in the flawed URL validation algorithm that fails to properly sanitize numeric representations of URLs. When developers implement redirect functionality using Django's built-in redirect mechanisms, they typically rely on is_safe_url() to validate destination URLs before performing redirects. However, the vulnerability allows attackers to craft malicious URLs that contain numeric representations which bypass the security checks. This occurs because the validation logic does not adequately distinguish between legitimate numeric URLs and potentially dangerous ones that could be exploited for phishing attacks or other malicious purposes. The vulnerability is classified under CWE-601 as an Open Redirect vulnerability, which represents a well-known security weakness where applications redirect users to external sites without proper validation.
The operational impact of CVE-2017-7233 extends beyond simple open redirects to include potential cross-site scripting attacks when developers improperly use the vulnerable function in their applications. When developers trust the output of is_safe_url() to provide safe redirect targets and subsequently embed these URLs in HTML links, they create an additional attack surface for XSS exploitation. Attackers can leverage this vulnerability to construct malicious URLs that appear legitimate to users while actually redirecting them to attacker-controlled domains. The vulnerability is particularly concerning because it affects core Django functionality that is widely used across web applications, potentially allowing attackers to craft convincing phishing campaigns that exploit the trust users place in legitimate application redirects.
Security professionals should note that this vulnerability aligns with ATT&CK technique T1566.001 for Phishing and T1566.002 for Spearphishing via Service, as attackers can use the open redirect to create convincing phishing attacks that leverage legitimate application redirects. The vulnerability demonstrates how seemingly minor flaws in URL validation can compound into significant security risks when combined with other application logic patterns. Organizations running affected Django versions should immediately upgrade to the patched releases to mitigate the risk of unauthorized redirects and potential XSS attacks. The remediation process involves updating to Django 1.10.7, 1.9.13, or 1.8.18 respectively, which contain the necessary fixes to properly validate numeric URLs and prevent the bypass of security checks. Additionally, developers should review their application code to ensure they are not relying on potentially vulnerable redirect logic and should implement additional input validation measures where redirect functionality is used.