MIME Types in WordPress

WordPress restricts both file types and MIME types, with additional types being added through code changes. In this article we explain what MIME types are, which MIME types WordPress allows to be uploaded, which MIME types WordPress recognizes, and how to add more MIME types if needed.

We’ll also explain why you may receive a security error when uploading an image, such as “Sorry, this file type is not permitted for security reasons” and how to fix this error.

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About MIME Types

MIME stands for Multipurpose Internet Mail Extensions. MIME types are used by browsers and other internet devices to determine the type of content associated with a page. For instance, if you have a .png file and a .jpeg file on the page, the browser would know by their MIME types to treat both files as images rather than videos or some other file types.

By default, WordPress has a list of registered mime types stored in wp-includes/functions.php that any developer can call using wp_get_allowed_mime_types(). These files are the file types recognized by WordPress. However, not all MIME types recognized are allowed to be uploaded through the WordPress Admin Dashboard. To see only the types that WordPress allows to be uploaded, you can use the upload_mimes filter.

If you attempt to upload a file where either the MIME type or file type are not supported by WordPress, you will get the error “Sorry, this file type is not permitted for security reasons.” Skip ahead to learn how to fix this error.

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Allowed WordPress MIME Types

Just because WordPress identifies a specific MIME type does not mean that the file type can be uploaded in your WordPress Admin Dashboard. WordPress restricts the file types that can be uploaded to the ones listed below.

Below is a list of the various file types that you can upload to WordPress, and the corresponding MIME type. These file types will upload without any security warnings in you wp-admin dashboard.

File Extension	MIME Type
.jpg	image/jpeg, image/pjpeg
.jpeg	image/jpeg, image/pjpeg
.png	image/png
.gif	image/gif
.ico	image/x-icon
.pdf	application/pdf
.doc	application/msword
.docx	application/vnd.openxmlformats-officedocument.wordprocessingml.document
.ppt	application/mspowerpoint, application/powerpoint, application/vnd.ms-powerpoint, application/x-mspowerpoint
.pptx	application/vnd.openxmlformats-officedocument.presentationml.presentation
.pps	application/mspowerpoint, application/vnd.ms-powerpoint
.ppsx	application/vnd.openxmlformats-officedocument.presentationml.slideshow
.odt	application/vnd.oasis.opendocument.text
.xls	application/excel, application/vnd.ms-excel, application/x-excel, application/x-msexcel
.xlsx	application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
.psd	application/octet-stream
.mp3	audio/mpeg3, audio/x-mpeg-3, video/mpeg, video/x-mpeg
.m4a	audio/m4a
.ogg	audio/ogg,
.wav	audio/wav, audio/x-wav
.mp4	video/mp4
.m4v	video/x-m4v
.mov	video/quicktime
.wmv	video/x-ms-asf, video/x-ms-wmv
.avi	application/x-troff-msvideo, video/avi, video/msvideo, video/x-msvideo
.mpg	audio/mpeg, video/mpeg
.ogv	video/ogg
.3gp	video/3gpp, audio/3gpp
.3g2	video/3gpp2, audio/3gpp2

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Not Allowed WordPress MIME Types

Using the wp_get_allowed_mime_types() function will give you a list of the MIME types WordPress recognizes, but does not allow to be uploaded. Below we’ll go over the MIME types that are not allowed to be uploaded in the wp-admin, but that WordPress still recognizes.

When uploading a file using one of the following extensions you will see the security warning “Sorry, this file type is not permitted for security reasons.” Skip to this section to learn how to resolve the error.

File Extension	MIME Type
.bmp	image/bmp
.tif	image/tiff
.tiff	image/tiff
.asf	video/x-ms-asf
.asx	video/x-ms-asf
.wm	video/x-ms-wm
.wmx	video/x-ms-wmx
.divx	video/divx
.flv	video/x-flv
.qt	video/quicktime
.mpe	video/mpeg
.webm	video/webm
.mkv	video/x-matroska
.txt	text/plain
.asc	text/plain
.c	text/plain
.cc	text/plain
.h	text/plain
.csv	text/csv
.tsv	text/tab-separated-values
.ics	text/calendar
.rtx	text/richtext
.css	text/css
.htm	text/html
.html	text/html
.m4b	audio/mpeg
.ra	audio/x-realaudio
.ram	audio/x-realaudio
.mid	audio/midi
.midi	audio/midi
.wax	audio/x-ms-wax
.mka	audio/x-matroska
.rtf	application/rtf
.js	application/javascript
.swf	application/x-shockwave-flash
.class	application/java
.tar	application/x-tar
.zip	application/zip
.gz	application/x-zip
.gzip	application/x-zip
.rar	application/rar
.7z	application/x-7z-compressed
.exe	application/x-msdownload
.pot	application/vnd.ms-powerpoint
.wri	application/vnd.ms-write
.xla	application/vnd.ms-excel
.xlt	application/vnd.ms-excel
.xlw	application/vnd.ms-excel
.mdb	application/vnd.ms-access
.mpp	application/vnd.ms-project
.docm	application/vnd.ms-word.document.macroEnabled.12
.dotx	application/vnd.openxmlformats-officedocument.wordprocessingml.template
.dotm	application/vnd.ms-word.template.macroEnabled.12
.xlsm	application/vnd.ms-excel.sheet.macroEnabled.12
.xlsb	application/vnd.ms-excel.sheet.binary.macroEnabled.12
.xltx	application/vnd.openxmlformats-officedocument.spreadsheetml.template
.xltm	application/vnd.ms-excel.template.macroEnabled.12
.xlam	application/vnd.ms-excel.addin.macroEnabled.12
.pptm	application/vnd.ms-powerpoint.presentation.macroEnabled.12
.ppsm	application/vnd.ms-powerpoint.slideshow.macroEnabled.12
.potx	application/vnd.openxmlformats-officedocument.presentationml.template
.potm	application/vnd.ms-powerpoint.template.macroEnabled.12
.ppam	application/vnd.ms-powerpoint.addin.macroEnabled.12
.sldx	application/vnd.openxmlformats-officedocument.presentationml.slide
.sldm	application/vnd.ms-powerpoint.slide.macroEnabled.12
.onetoc	application/onenote
.onetoc2	application/onenote
.onetmp	application/onenote
.onepkg	application/onenote
.odp	application/vnd.oasis.opendocument.presentation
.ods	application/vnd.oasis.opendocument.spreadsheet
.odg	application/vnd.oasis.opendocument.graphics
.odc	application/vnd.oasis.opendocument.chart
.odb	application/vnd.oasis.opendocument.database
.odf	application/vnd.oasis.opendocument.formula
.wp	application/wordperfect
.wpd	application/wordperfect
.key	application/vnd.apple.keynote
.numbers	application/vnd.apple.numbers
.pages	application/vnd.apple.pages

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Additional File Types

If you need to use other file types with WordPress beyond what it identifies already, it simplest to use a plugin to extend this function, for example WP Add Mime Types. Doing this is most often necessary with file types that are not images. Common examples include .epub or .mobi files from eBooks.

If you need a complete reference of which MIME types exist, see this comprehensive list.

If you’re still having issues, another potential solution is to add the following to your wp-config.php file. This allows uploading of non-image file types just for administrator-level users.

define( 'ALLOW_UNFILTERED_UPLOADS', true );

To modify the wp-config file connect with either SFTP or SSH Gateway.

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Non-Image File Upload Error

In the security patch for WordPress 4.7.1 which was released in January 2017, a change to the way WordPress checks the file “MIME type” for uploads was made, which may cause a security error on uploads for some file types (specifically non-image files).

Some users, especially those using custom plugins to add additional file types to the ones WordPress allows by default (found here) may experience this error when uploading to the wp-admin:

“filename” has failed to upload.
Sorry, this file type is not permitted for security reasons.

This security error is most often see with files using the extensions: .docx, .ppt, .svg, .xlsm, .ai but may display for may more file types. If you’ve just started seeing this warning you may be wondering how to fix this error. There are a couple different ways to resolve the issue:

1. Add the following line to the wp-config.php file. This will allow non-image uploads for administrators only:
   • define( 'ALLOW_UNFILTERED_UPLOADS', true );
   • To modify the wp-config file connect with either SFTP or SSH Gateway
2. Use a plugin that restores this ability, such as WP Add MIME Types
3. Upload the file that is returning the error using SFTP instead

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