A common task that can be very dangerous. People can upload a file and then execute that file on your server. In <cffile>, many peole use the accept="" attribute to limit the kinds of files you can upload, but this isn't the greatest approach. A hacker can spoof the mime type. So, could upload a ColdFusion page, spoof the mime type, and execute the ColdFusion page. This spoofing can easily be done with ColdFusion.
Best practices: Upload to a directory outside the web root or to a static content server. Always check the file extension (cffile.serverFileExt), although this is obviously not reliable, but it would stop someone from executing a ColdFusion page when it has an image mime type (as an example). Use the accept="" attribute, just don't rely on it. Also check the filename to avoid XSS. Otherwise, a person could have JavaScript in the filename that could be executed. The combination of these things would make it very challenging to exploit uploading.
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