![]() ![]() ![]() ![]() MIME type guessing has led to security exploits in Internet Explorer based on malicious authors incorrectly reporting a MIME type of a dangerous file as a safe type. For example, an executable program should not be executed on the user’s computer, and at most should cause a dialog to appear asking the user if they wish to download the file. For this reason, the actions a browser can take when given content of that type are usually restricted. Some content types, such as executable programs, are inherently unsafe. If the browser guesses the MIME type, this option is no longer available to the author. If the browser ignores the reported MIME type, web administrators and authors no longer have control over how their content is to be processed.įor example, a website oriented for web developers might wish to send certain example HTML documents as either text/html or text/plain in order to have the documents either processed and displayed as HTML or as source code. ![]() Why browsers should not guess MIME typesĪpart from violating the HTTP specification, it is a bad strategy for browsers to guess MIME types for the following reasons. Serving content using the correct MIME type can also be important for security reasons it’s possible for malicious content to affect the user’s computer by pretending to be a safe type of document when it is in fact not. This has sheltered many web administrators from their own errors as, using this method, Internet Explorer will continue to process content as expected even though the web server is misconfigured, e.g., it may correctly display an image that is reported to be plain text. Some other web browsers, such as Internet Explorer, try to allow for misconfigured web servers and applications by guessing what the correct MIME type should be. If the web server or application reports an incorrect MIME type for content, a web browser has no way, according to the HTTP specification, of knowing that the author actually intended the content to be processed and displayed in a way different from that implied by the reported MIME type. The HTTP specification defines a superset of MIME which is used to describe the media types used on the web. MIME is currently defined in RFCs 2045, 2046, 2047, 2048, and 2049 registered values for MIME types are available in IANA/MIME Media Types. This is a major source of problems for users of Gecko-based browsers, which respect the MIME types as reported by web servers and web applications. As new content types are invented or added to web servers, web administrators may fail to add the new MIME types to their web server’s configuration. application/pdf for Adobe ® PDF documents.īy default, many web servers are configured to report a MIME type of text/plain or application/octet-stream for unknown content types.application/x-java-applet for Java ™ applets.application/octet-stream meaning “download this file”.MIME types-also sometimes called Internet media types or Content-types-describe the media type of content either contained in email or served by web servers or web applications, and are intended to help guide a web browser to correctly process and display the content. Some of these players are built into the client, typically a browser (for example, all browsers come with GIF and JPEG image players, as well as the ability to handle HTML files) other players may need to be downloaded. Clients use this header to select an appropriate display, or "player", application for the type of data indicated by the header. Servers insert the MIME header at the beginning of any web transmission. In 1991, the protocol was extended so that Internet clients and servers could recognize and handle various kinds of data, and new file types were added to the “mail” protocol as supported Internet Protocol file types. MIME (Multi-purpose Internet Mail Extensions) is an expansion of the original Internet e-mail protocol that exchanges different kinds of data files on the Internet: text, audio, video, images, application programs, and others. Common MIME types are for example text/html for html-files or image/jpeg for jpeg-files. As a result the browser is able to choose a suitable displaying method. MIME types enable browsers to recognize the filetype of a file which has been sent via HTTP by the webserver. ![]()
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