CVE-2020-25626 in Django REST Framework
Summary
by MITRE • 10/04/2020
A flaw was found in Django REST Framework versions before 3.12.0 and before 3.11.2. When using the browseable API viewer, Django REST Framework fails to properly escape certain strings that can come from user input. This allows a user who can control those strings to inject malicious <script> tags, leading to a cross-site-scripting (XSS) vulnerability.
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Analysis
by VulDB Data Team • 11/15/2020
The vulnerability identified as CVE-2020-25626 represents a critical cross-site scripting flaw within the Django REST Framework that affects versions prior to 3.12.0 and 3.11.2. This security issue manifests specifically within the browseable API viewer component of the framework, which serves as a web interface for developers to interact with and test API endpoints. The vulnerability stems from inadequate input sanitization mechanisms that fail to properly escape user-controllable strings, creating a pathway for malicious actors to inject harmful script content into the application's response. The affected component operates as a user-facing interface that displays API documentation and allows interactive testing of endpoints, making it a prime target for exploitation.
The technical flaw resides in the improper handling of HTML escaping within the browseable API viewer's rendering process. When user input flows through the framework's rendering pipeline to the web interface, the system fails to adequately sanitize special characters that could be interpreted as HTML or JavaScript markup. This deficiency allows attackers to inject malicious script tags directly into the response, particularly when user-controlled parameters are displayed within the API documentation interface. The vulnerability specifically impacts scenarios where the framework displays user-generated content such as parameter values, response data, or custom documentation elements that are not properly escaped before being rendered in the browser context. This issue falls under the CWE-79 classification for Cross-Site Scripting and aligns with ATT&CK technique T1203 for Exploitation for Client Execution.
The operational impact of this vulnerability extends beyond simple data theft or defacement, as it enables attackers to execute arbitrary JavaScript within the context of authenticated users' browsers. An attacker who can control input parameters or manipulate API responses can leverage this vulnerability to perform session hijacking, steal authentication tokens, redirect users to malicious sites, or perform actions on behalf of authenticated users. The vulnerability is particularly concerning because it affects the framework's built-in API documentation interface, which is typically accessible to developers and authorized users, making it easier to exploit in real-world scenarios. The attack surface is broad as it can be triggered through various input points within the API testing interface, including query parameters, request bodies, and response data that gets displayed in the browseable format.
Mitigation strategies for CVE-2020-25626 primarily involve upgrading to Django REST Framework versions 3.11.2 or 3.12.0, which contain the necessary patches to properly escape user-controllable strings in the browseable API viewer. Organizations should conduct thorough testing of their API interfaces to identify any custom implementations that might be vulnerable, as third-party extensions or custom templates could also be affected. Security teams should implement additional safeguards such as content security policies that limit script execution within the API documentation interface, and consider disabling the browseable API in production environments where it is not strictly necessary. The fix implemented by the Django REST Framework team involves strengthening the HTML escaping mechanisms within the rendering pipeline to ensure that all user-controllable content is properly sanitized before being displayed in the web interface, addressing the root cause of the vulnerability through proper input validation and output encoding practices.