Files have signatures or 'magic numbers' embedded in them, usually near the beginning of the file. Libmagic is a library which extracts a files signature and looks it up in a signature database. This is the way Unix type systems determine file types i.e.

If you save a text file without an extension on Linux it will still automatically open with a text editor. Systems like Windows on the other hand only look at file extension. Opening a text file with no extension on Windows will result in a WTf-is-this popup window.

So there are merits in checking both the extension and the magic number since your website will likely have visitors with different operation systems. True, although I would add that not all files have magic numbers. In particular, Linux-like systems tend to recognize a text file by its lack of a known magic number.

Is there a tool that can determine the file type from containing data? How can I detect if the extension of a file has been modified? How to get(extract) a file extension in PHP? The simplest way to get file extension in php is to use php built-in function pathinfo. $file_ext = pathinfo.

Mime_content_type (PHP 4 >= 4.3.0, PHP 5, PHP 7) mime_content_type — Detect MIME Content-type for a file. Smart File Type Detection Using PHP. In most web applications today, there is a need to allow users to upload images, audio and video files. Sometimes, we also need.

And depending on which program is doing the interpretation, a known file extension could override the type determination from the magic number. (which is occasionally desirable) I would say only that Linux file managers base their determination of the file type on the file's content and its name, whereas Windows Explorer bases it solely on the extension. – May 13 '14 at 16:06. The $_FILES contains mime types as well, you can check that. You can parse the files with a specific parser which throws an exception when the file is not really what it waits. Omnicron Alarm Manual here. Anything else can be falsified I think. For example you can use GD or Imagick by image files, a JSON parser by json files, DOM and XML parser (with turned off external entities) by HTML and XML files, etc.

By Imagick you can use the as well. Batman Dark Moon Rising Pdf. I think there are other tools for other file types. What really matters by file upload is • preventing execution (Use chmod() to change file attributes, and/or move them to a static subdomain.), • file inclusion (Never include an uploaded file by serving the clients, use file reading methods like file_get_contents(), or use the X-Sendfile header without HTTP header injection vulnerability, if you want to have access control on the file.

If not, then let the HTTP server do its job.), • eval injection (Never use exif data in an eval context, for example with preg_replace().), • content sniffing (Force download with Content-Disposition header without HTTP header injection vulnerability, or by inclusion use the following headers: Strict-Transport-Security, X-Content-Type-Options, X-Frame-Options, X-XSS-Protection, Content-Security-Policy.) • xss (The same as by content sniffing. Try to avoid client side file inclusion, if not necessary, and use the proper headers.) and so on. I wrote an even more about PHP uploads, maybe it helps. Salvador Dali has some very good suggestions with regards to images. 1 thing however that he is missing.

It is possible for an image to show as perfectly valid however contain malicious code. This for example can be placed after the end of image marker (0xFF, 0xD9). 1 potential way to get around this is to re sample the file using something like GD.

It used to be quite common for avatar and signature uploads to be taken advantage of in forums. Someone would upload their image which will display as normal but will also contain code that could infect the users PC with malware. The same is probably also true for MP3's and other file types.