U4-6873 - Adding nosniff-header breaks PNG-images in Internet Explorer

Created by Jeffrey Schoemaker 24 Jul 2015, 15:07:24 Updated by Sebastiaan Janssen 05 Jan 2016, 09:55:06

Relates to: U4-629

Relates to: U4-694

Summary: If you add a png-image to the mediasection, Umbraco will create a .jpg-thumbnail, but this file isn't a real .jpg but actually a .png that is stored as a jpg. This issue has been in the Umbraco core since a few years, but we didn't have any issues (although it was wrong). A few weeks ago we had to add a security-header ("no-sniff") to all our websites and then Umbraco breaks, because Internet Explorer won't display the images any longer.

Details: https://our.umbraco.org/forum/umbraco-7/using-umbraco-7/66788-adding-nosniff-header-breaks-png-images-in-internet-explorer#comment-222740

Related issues:

• http://issues.umbraco.org/issue/U4-694
• http://issues.umbraco.org/issue/U4-629

Fix: https://github.com/umbraco/Umbraco-CMS/pull/747

We tested the code pretty good with several examples in different use cases and we think it will fix this issue and won't introduce other issues, but please test properly. If you upgrade your Umbraco with this fix new thumbnails will probably be generated by Umbraco (happens now too if the thumbnail gets deleted). But if your old code expect always a .jpg-thumbnail in your usercontrols/views/etcetera your code will not work any longer because now the proper. In that way you could see this is a "breaking" change.

Hope you like it,

Jeffrey

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