Scope:
All Barracuda Web Filters, all firmware versions.
Answer:
When entering MIME types into the Block/Accept > MIME Type Blocking page, make sure you enter the entire MIME type in the following format:
image/jpeg
If you only enter the first part or second part, or if you leave out the slash, the Barracuda Web Filter will not properly recognize and catch the MIME type you are trying to block. You can find a complete list of MIME types here [1]https://www.iana.org/assignments/media-types/media-types.xhtml
MIME type blocking works by matching the MIME type that is presented by the web server when the download is requested. There is no formal requirement for web servers to provide this information and in some cases there are more than one MIME type used for the same file type. For example .exe files can be application/octet-stream , application/x-sdlc or application/x-msdos-program.
One easy way to identify the MIME type being presented by the web server can be done with most modern browsers. Enable the developer console in your browser and attempt to download the file you are blocking. Typically the information needed is displayed in the tab called Network. As you can see in the highlighted portion of the image below, when downloading the Java installer the far left column shows the name of the file “chromeinstall-7u67.exe” and shows a type of application/x-sdlc . To block downloads of this file you would need to add this to the MIME types to block in the Web Filter under Block/Accept > MIME type blocking you would enter application/x-sdlc.
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