CVE-2021-46898 in django-grappelli
Summary
by MITRE • 10/25/2023
views/switch.py in django-grappelli (aka Django Grappelli) before 2.15.2 attempts to prevent external redirection with startswith("/") but this does not consider a protocol-relative URL (e.g., //example.com) attack.
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Analysis
by VulDB Data Team • 11/12/2023
The vulnerability identified as CVE-2021-46898 affects django-grappelli, a popular Django admin interface enhancement package, specifically in versions prior to 2.15.2. This security flaw resides within the views/switch.py file and represents a critical issue in the application's redirection handling mechanism. The vulnerability stems from an insufficient validation approach that attempts to prevent external redirection attacks by checking if URLs start with a forward slash character. This simplistic validation method fails to account for protocol-relative URLs, which can bypass the intended security controls and enable malicious redirection attacks.
The technical implementation of this vulnerability demonstrates a classic input validation flaw that can be categorized under CWE-601, which specifically addresses URL redirection vulnerabilities. The flaw occurs when the application processes user-provided redirect parameters without proper sanitization of protocol-relative URLs. In the context of web applications, protocol-relative URLs are those that begin with double forward slashes, such as //example.com, which inherit the protocol (http or https) from the current page context. This characteristic allows attackers to craft malicious URLs that appear to be internal but actually redirect to external domains, bypassing the intended security checks that only verify the presence of a leading forward slash.
From an operational perspective, this vulnerability poses significant risks to applications using django-grappelli, as it enables open redirect attacks that can be exploited for phishing campaigns, credential theft, or malware distribution. Attackers can manipulate the redirect functionality to send users to malicious websites while maintaining the appearance of legitimate internal navigation. The impact extends beyond simple redirection, as this vulnerability can be chained with other attacks to create more sophisticated exploitation scenarios. The vulnerability affects the authentication and authorization mechanisms within the Django admin interface, potentially allowing attackers to compromise user sessions or gain unauthorized access to administrative functions.
Security professionals should note that this vulnerability aligns with ATT&CK technique T1566.002, which covers "Phishing: Spearphishing Attachment," as attackers can leverage open redirect vulnerabilities to deliver malicious payloads through deceptive links. The flaw also relates to ATT&CK technique T1071.004, covering "Application Layer Protocol: DNS," as malicious redirection can be used to manipulate DNS resolution or direct users to malicious DNS servers. Organizations using django-grappelli should prioritize immediate patching to version 2.15.2 or later, as the fix addresses the core validation logic to properly handle protocol-relative URLs. Additionally, implementing proper input sanitization, validating all redirect parameters against a strict allowlist of approved domains, and monitoring for suspicious redirect patterns can serve as effective mitigations. The vulnerability highlights the importance of comprehensive security testing, particularly for authentication and authorization components, and demonstrates the necessity of considering edge cases in URL validation logic.