![]() This works for GIF, JPEG, and PNG only, of course, and you may run into some issues like alpha channel and colour profile problems. This would erase any ID3 and other header information contained in the file, and probably destroy any exploit attempts (GD would probably choke on such a file and return an error). You could however, to provide totally maximum security, of course copy the image into a new image container using GD's imagecopy. Make sure you read post below and follow the link, it contains a bunch of great information on other security aspects when dealing with files. So, as long as you make sure you use is_uploaded_file() and move_uploaded_file() when handling the upload, you should be fine, at least on the image format front. This is impossible to protect effectively against from server side and is the browser vendor's responsibility. The only security breach imaginable using a forged image file would be something that exploits the browser's rendering engine. by using include()), that is not a problem and you do not need to check for PHP code or anything else. But as long as you're not going to execute the file (e.g. “shell.php/” or “scri[t.php.\”).įile upload vulnerabilities are very common when conducting a penetration test against web applications, knowing how to bypass file restrictions is key as these will often result in a full system compromise.Neither file extension nor mime type can give you 100% security that you are dealing with a image file. Although slash or backslash characters are unlikely to succeed as they are normally used to separate directories, they are worth a try (e.g. Special characters like spaces or dots in Windows or dots and slashes in a Linux at the end of a filename will be removed automatically (e.g. Try adding neutral characters after the filename ![]() ![]() filename=’web”config’ to replace the “web.config” file). In order to include the double quote character in the filename in a normal file upload request, the filename in the “Content-Disposition” header should use single quotes (e.g. “web<<” can replace the “web.config” file). Try finding characters that are converted to other useful characters during the file upload process.įor instance, when running PHP on IIS, the “>”, “<”, and double quote “ characters respectively convert to “?”, “*”, and “.” characters that can be used to replace existing files (e.g. For example shell.aspx will become SHELL~1.ASP The Windows 8.3 short name version can be used in the file name. Try using Windows 8.3 notation for the file name php can help bypass file extension whitelistsĪn executable script can be inserted into an image in the form of a metadata comment, which will then be executed when the web server uses the image in a page In order webservers, adding special characters such as %$
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