I'm looking to customize/change thefor (failed) logins. As recently as WHM 11.28 the failurls file was located in /var/cpanel/failurls, but it's not there now in 11.32.3. I understand there was a security issue, from cPanel HTTP Response Splitting Vulnerability - cPanel Inc.
But I can't find anywhere to whitelist failurl.The ‘failurl’ parameter is not used in the default cPanel UI. Custom login pages and forms used by third parties do make use of this parameter. Beginning in cPanel 11.25.0 Build 43786 only ‘failurl’ values whitelisted by the system administrator will be processed by cPanel.