Admin Login form empty after upgrade to 1.9.4.2

Question

After upgrading from 1.9.4.1 to 1.9.4.2, the login form for the backend is empty (No input tags for username or password). This is same after cache has been cleared. Does anyone have a solution?

The call to this->getFormKey(); appears to be causing the problem.

<input name="form_key" type="hidden" value="<?php echo $this->getFormKey() ?>" />

Answer 1

I ended up discovering the issue. At some point app/code/core/Mage/Core/functions.php was copied to app/code/local/Mage/Core/functions.php to fix a compatibility issue. Therefor after updating, I was missing a patch to functions.php which include defining random_int() for PHP versions less than 7. This method is used to generate the form key.