Wrong reference to big-f0f0f0.gif in xtheme-t3skin.css
in TYPO3 8.7.30 (and all previous versions of TYPO3 8.7 too) in file typo3/sysext/core/Resources/Public/ExtJs/xtheme-t3skin.css in line 493 and 517 are references to ../images/spinner/big-f0f0f0.gif for the background-image url.
The folder typo3/sysext/core/Resources/Public/images/spinner doesn't exist. The file big-f0f0f0.gif resides in folder typo3/sysext/core/Resources/Public/ExtJs/images, so it should be:
Updated by Tobias Schaefer over 1 year ago
Thank you for the quick response. Of course I hoped that this easy to fix bug would be fixed.
But I understand that you want to concentrate on newer TYPO3 versions.
In my case this bug is critical because the backend users will get blocked by fail2ban (https://www.fail2ban.org/) if a request for a non-existing file happens.
Fail2ban is installed mainly to block hackers (not backend users) but it doesn't distinguish between failing request from the frontend or backend.
I solved it for me by correcting the stylesheet with an extension ($GLOBALS['TBE_STYLES']['skins'][$_EXTKEY]['stylesheetDirectories']['css'] = 'EXT:'.$_EXTKEY.'/Resources/Public/Css/backend/';).