Magento has released a patch that provides support for PHP 7.2.x for Magento Commerce 1.14.2.x and 1.14.3.x, as well as Magento Open Source 1.9.2.x and 1.9.3.x Going forward, support for PHP 7.2 will be included as part of the Magento Commerce 126.96.36.199 and Magento Open Source 188.8.131.52 releases, which are currently scheduled for late 2018.
Important note: While this patch resolves compatibility issues with the core Magento code, you must also update any extensions and customizations.
Magento Commerce customers can find patch options under Magento Commerce 1.x > Support Patches and Security Patches > PHP Compatibility patches in the Downloads section of their account and there are separate patches for versions 184.108.40.206 to 220.127.116.11, 18.104.22.168, and 22.214.171.124 to 126.96.36.199 (note this last patch is compatible with the recently released version 188.8.131.52):
Magento Open Source merchants can download the following patches from Magento Tech Resources and again there are separate patches for versions 184.108.40.206 to 220.127.116.11, 18.104.22.168, and 22.214.171.124 to 126.96.36.199 (this last patch is also compatible with recently released version 188.8.131.52):
Magento have run a series of tests with these patches but no testing can cover every single scenario. Therefore, as with any changes applied to a live site, we always recommend testing these first on a test or staging area and then always ensuring full backups are taken before moving ahead on your live site. Before changing the account to PHP 7.2, ensure you check and test all third party components are also compatible with PHP 7.2