A security vulnerability has been recently discovered in the popular web development framework, Django. This issue, identified as CVE-2024-39330, impacts versions 5. before 5..7 and 4.2 before 4.2.14. Derived classes of the django.core.files.storage.Storage base class, when they override generate_filename() without replicating the file-path validations from the parent class, are potentially vulnerable to directory traversal attacks via certain inputs during a save() call. Thankfully, built-in Storage sub-classes are unaffected.

In this post, we will delve into the details of this exploit, providing code snippets for better understanding and links to the original references for further information.

Vulnerability Details

To understand this vulnerability, let's first look at the generate_filename() method in the Storage base class within Django.

def generate_filename(self, filename):
    """
    Apply any processing that is required to the filename before
    using it. By default, this does nothing.
    """
    return filename

As you can see, the base implementation of this method does not do any processing on the filename. However, when a derived class overrides this method, it should replicate the file-path validations provided by the parent class.

Here is an example of a vulnerable derived class that does not replicate the file-path validations

# Bad Example
class VulnerableStorage(Storage):
    def generate_filename(self, filename):
        # Custom processing code that ignores parent implementation and validations
        return some_custom_processing_function(filename)

In this example, there is a possibility of a directory traversal attack. An attacker could potentially manipulate the filename input during a save() call and access files outside the intended directory.

Exploit Details

An attacker can exploit this vulnerability by crafting a malicious filename input during a save() call in a Django web application if it uses a derived class of the Storage base class that overrides the generate_filename() method without replicating the file-path validations found in the parent class. This could potentially lead to unauthorized file access and compromise the security of the web application.

Mitigation and Fix

To fix this vulnerability, derived classes should implement the file-path validations present in the parent class while overriding the generate_filename() method. Check the following code snippet for a recommended implementation.

# Good Example
class SafeStorage(Storage):
    def generate_filename(self, filename):
        # Custom processing code while ensuring parent implementation and validations
        filename = super().generate_filename(filename)
        return some_custom_processing_function(filename)

The Django project has released updates to address this issue, and it is highly recommended to update your Django version to the latest, secure release.

You can find more information about CVE-2024-39330 and the related updates from the following sources:

1. Django Security Advisory
2. Django GitHub Repository
3. CVE-2024-39330 Record on NIST

Conclusion

CVE-2024-39330 is a significant security vulnerability found in specific versions of the Django web development framework. This issue affects derived classes of the django.core.files.storage.Storage base class when they override the generate_filename() method without incorporating the file-path validations from the parent class. Users of vulnerable Django versions should upgrade to the latest release with the provided security patch as soon as possible.

Timeline

Published on: 07/10/2024 05:15:12 UTC
Last modified on: 07/11/2024 13:05:54 UTC