vulnerabilities-workflow-1.md

• Vulnerability Name: Unauthenticated Arbitrary File Upload via Attachment Endpoint Due to Inadequate File Type Validation

  • Description: An external attacker can exploit the file upload endpoint at /summernote/upload_attachment/ to store arbitrary files on the server without authentication. This vulnerability arises because the server-side validation of uploaded files is insufficient. In scenarios where the Pillow library (used for image validation) is not installed, the application falls back to using a generic FileField instead of ImageField in the upload form. Even when Pillow is installed and ImageField is used, basic image validation can be bypassed by uploading specially crafted files that are valid image formats but contain malicious payloads (e.g., SVG files with embedded JavaScript or HTML files disguised as images). These uploaded files are then saved in the publicly accessible media directory. If the web server is misconfigured to serve static files from the media directory and allows direct access, an attacker can access and potentially execute these malicious files. This can lead to Cross-Site Scripting (XSS) if malicious scripts are embedded in uploaded files (like SVG or HTML) and Remote Code Execution (RCE) if the server is further misconfigured to execute certain file types from the media directory (e.g., PHP or other executable scripts).

  • Impact: This vulnerability can lead to several severe security impacts:

    • Cross-Site Scripting (XSS): By uploading files containing malicious scripts (e.g., JavaScript in SVG or HTML), an attacker can inject these scripts into web pages served by the application. When other users view content containing the uploaded malicious file, the script can execute in their browsers. This can result in session hijacking, website defacement, redirection to malicious sites, or theft of sensitive information.
    • Remote Code Execution (RCE): If the web server is misconfigured to execute files from the media directory (where uploaded files are stored), an attacker could upload and execute arbitrary code on the server. This can lead to a complete compromise of the application and the server, allowing the attacker to gain full control, access sensitive data, modify application functionality, or use the compromised server for further malicious activities, including lateral movement within the hosting environment.
    • Website Defacement and Data Manipulation: Attackers can upload files that deface the website or manipulate data presented to users, damaging the reputation and integrity of the application.
    • Resource Exhaustion: While not the primary impact, attackers could potentially upload very large files to exhaust server storage space or bandwidth, leading to denial of service.

  • Vulnerability Rank: High

  • Currently Implemented Mitigations:

    • Basic Image Validation (with Pillow): When the Pillow library is installed, Django's ImageField in the UploadForm attempts to validate if uploaded files are valid images. However, this validation is not robust and can be bypassed with crafted image files.
    • File Size Limit: The attachment_filesize_limit configuration sets a limit on the size of uploaded files, which can help mitigate some denial-of-service scenarios but does not prevent malicious file uploads.
    • Optional Authentication: The attachment_require_authentication setting allows requiring user authentication for file uploads. When enabled, it reduces the attack surface to authenticated users but does not eliminate the vulnerability for authorized users.
    • Custom Authorization Logic: The test_func_upload_view setting allows for implementing custom authorization logic for the upload view, providing a way to add more restrictive access controls, but it relies on proper configuration by the application developer.
    • X-Frame-Options Header: The @method_decorator(xframe_options_sameorigin) decorator sets the X-Frame-Options header to SAMEORIGIN for the upload view, mitigating clickjacking attacks on the upload endpoint itself.
    • Content Sanitization (for Editor Content): The bleach library is used in SummernoteTextFormField and SummernoteTextField to sanitize content within the Summernote editor, which helps prevent XSS from user-provided text content but does not directly address the file upload vulnerability.

  • Missing Mitigations:

    • Robust File Type Validation: Implement more thorough file validation beyond basic image format checks. This should include:
      • Magic Number Checks: Verify file types based on their content (magic numbers) to ensure they match the expected file type, regardless of the file extension.
      • Deep Content Inspection: Use libraries that deeply inspect file content to ensure they are truly of the expected type and do not contain embedded malicious code. For example, for SVG files, check for <script> tags and event handlers.
      • MIME Type Validation: Perform server-side MIME type validation to verify the declared MIME type of the uploaded file against its actual content.
      • File Type Whitelisting: Explicitly whitelist allowed file types and reject all others.
    • Input Sanitization of Uploaded Filenames: Sanitize filenames to prevent potential path traversal or other issues if filenames are used in insecure ways during retrieval or display.
    • Content Security Policy (CSP): Implement CSP headers to restrict the sources from which scripts can be executed and other resources can be loaded. This can significantly mitigate the impact of XSS if malicious scripts are uploaded, even if they are served.
    • Secure Media Directory Configuration: Provide clear guidelines and warnings in documentation about the security risks of serving media files directly as static files. Recommend best practices for securing media directories, such as:
      • Disabling execution of scripts and other executable files from the media directory in the web server configuration.
      • Using a dedicated, isolated storage for user-uploaded files, separate from the web server's document root.
      • Implementing access control mechanisms for media files to restrict access only to authorized users or contexts.
    • Regular Security Audits and Penetration Testing: Conduct regular security audits and penetration testing to identify and address potential vulnerabilities, including file upload vulnerabilities.

  • Preconditions:

    • The disable_attachment setting is set to False, enabling the attachment feature.
    • The application is deployed in an environment where the Pillow library might not be installed, or even if installed, the basic ImageField validation is relied upon without further robust checks.
    • The attachment_require_authentication setting is set to False (default), allowing unauthenticated users to upload attachments, or the vulnerability is exploitable by authenticated users if authentication is required.
    • The web server is configured to serve files from the media directory as static files and allows direct access to this directory. This is a common configuration in development and some production environments that are not properly secured.

  • Source Code Analysis:

    • django_summernote/forms.py - UploadForm Definition:

      from django import forms
      try:
          from PIL import Image  # noqa: F401
          FIELD = forms.ImageField
      except ImportError:
          FIELD = forms.FileField
      
      class UploadForm(forms.Form):
          file = FIELD(required=True)

      • This code block shows that the UploadForm dynamically chooses between forms.ImageField and forms.FileField based on the availability of the Pillow library.
      • If Pillow is successfully imported, FIELD is set to forms.ImageField, which performs basic image validation by attempting to open the uploaded file as an image.
      • If Pillow is not found (ImportError), FIELD defaults to forms.FileField, which performs no specific file type validation beyond checking if a file was uploaded. This fallback makes the application vulnerable to arbitrary file uploads when Pillow is not installed.

    • django_summernote/views.py - SummernoteUploadAttachment.post Method:

      def post(self, request, *args, **kwargs):
          # ...
          if not request.FILES.getlist('files'):
              return JsonResponse({
                  'status': 'false',
                  'message': _('No files were requested'),
              }, status=400)
      
          for file in request.FILES.getlist('files'):
              form = UploadForm(
                  files={
                      'file': file,
                  }
              )
              if not form.is_valid():
                  # ... error handling ...
              else:
                  attachment = Attachment()
                  attachment.file.save(file.name, file)
                  attachment.name = file.name
                  attachment.save()
                  return JsonResponse({
                      'url': attachment.file.url,
                      'name': attachment.name,
                  })
          return JsonResponse({'status': 'false', 'message': _('Unknown error')}, status=400)

      • This code snippet demonstrates how the SummernoteUploadAttachment view handles POST requests for file uploads.
      • It retrieves uploaded files from request.FILES.getlist('files').
      • For each uploaded file, it instantiates an UploadForm to validate the file.
      • The crucial part is that the validation is performed using the UploadForm, which, as shown in forms.py, may use either forms.ImageField or forms.FileField.
      • If the form is valid (meaning the file passed the validation, which might be minimal if Pillow is not installed or if a crafted image is uploaded), the file is saved using the Attachment model, and its URL is returned in a JSON response.
      • This process confirms that without robust file validation beyond forms.ImageField (or no validation at all with forms.FileField), arbitrary files can be uploaded and stored.

  • Security Test Case:

    1. Prepare the Environment:

       • Set up a test deployment of the application with django-summernote integrated.
       • Optionally, remove the Pillow library to test the FileField fallback scenario (using pip uninstall Pillow). Alternatively, keep Pillow installed to test bypass using crafted images.
       • Ensure that disable_attachment is set to False and attachment_require_authentication is set to False in the application's settings.
       • Verify that the media directory is publicly accessible and that the web server serves static files from this directory.

    2. Craft Malicious Files:

       • Malicious SVG file (for XSS): Create a file named malicious.svg with the following content:

         <svg xmlns="http://www.w3.org/2000/svg">
           <script>alert("XSS Vulnerability in django-summernote");</script>
         </svg>

         Rename this file to malicious.png to attempt to bypass basic extension-based checks and target ImageField validation.
       • Malicious HTML file (for HTML upload test): Create a file named malicious.html with the following content:

         <html>
         <body>
         <h1>Malicious HTML File</h1>
         <script>alert("HTML Upload Test");</script>
         </body>
         </html>

         Rename this file to malicious_html.png.

    3. Access the Summernote Editor:

       • Navigate to a page in the application where the Summernote editor is used (e.g., admin panel, a blog post creation form, or a test page with Summernote).

    4. Initiate File Upload:

       • In the Summernote editor toolbar, locate the "Image" upload button and click it to open the file upload dialog.

    5. Upload Malicious Files:

       • Upload malicious.png (the SVG file renamed to .png) and malicious_html.png (the HTML file renamed to .png) one at a time through the Summernote editor's image upload functionality.

    6. Verify Successful Upload:

       • After each upload, check the HTTP response. A successful upload should return a 200 status code and a JSON response containing the URL of the uploaded file. Note down these URLs.

    7. Test XSS (SVG):

       • Insert the uploaded malicious.png (SVG) image into the Summernote editor content.
       • Save the content.
       • View the saved content in a browser outside of the editor (e.g., on the public-facing frontend or by viewing the saved content in the admin panel).
       • Observe if an alert box with the message "XSS Vulnerability in django-summernote" appears. If it does, XSS is confirmed.

    8. Test HTML Upload (Direct Access):

       • Open a new browser tab and directly access the URL of the uploaded malicious_html.png file (obtained in step 6).
       • Observe if the HTML content is rendered and if the JavaScript alert "HTML Upload Test" is executed. If the HTML is rendered and the alert appears, it confirms that HTML files can be uploaded and directly accessed/executed, highlighting a more severe risk depending on server configuration.

    9. Conclusion:

       • If the malicious SVG file triggers an XSS alert and/or the malicious HTML file is rendered/executed when accessed directly, the unauthenticated arbitrary file upload vulnerability is confirmed. This demonstrates the ability to upload and potentially execute malicious content due to inadequate file type validation in django-summernote.