PRACTITIONER File path traversal, validation of file extension with null byte bypass How to prevent a path traversal attack The following is an example of an equivalent attack against a Windows-based server: \ are valid directory traversal sequences. On Unix-based operating systems, this is a standard file containing details of the users that are registered on the server, but an attacker could retrieve other arbitrary files using the same technique. sequences step up from /var/www/images/ to the filesystem root, and so the file that is actually read is: is valid within a file path, and means to step up one level in the directory structure. This causes the application to read from the following file path: As a result, an attacker can request the following URL to retrieve the /etc/passwd file from the server's filesystem: This application implements no defenses against path traversal attacks. The image files are stored on disk in the location /var/In other words, the application reads from the following file path: The loadImage URL takes a filename parameter and returns the contents of the specified file. This might load an image using the following HTML: Imagine a shopping application that displays images of items for sale. Reading arbitrary files via path traversal
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