it probably starts with a correct and safe authorization check, but this vulnerability happens before any user code runs, so every PHP page is vulnerable.
True-ish? If your firewall's admin page is internet-accessible, you have no excuse for not doing "bolted to bedrock" lockdowns of your web server config and your PHP config. Either of which could have blocked exploitation of the PHP vuln.
Then similar for your web server (Apache, nginx, whatever).
EDIT: About your "would've seemed adequate before this" - I dug up a copy of a PHP v5.2 php.ini file (2-ish decades ago). That file begins thus:
;;;;;;;;;;;
; WARNING ;
;;;;;;;;;;;
; This is the default settings file for new PHP installations.
; By default, PHP installs itself with a configuration suitable for
; development purposes, and *NOT* for production purposes.
; For several security-oriented considerations that should be taken
; before going online with your site, please consult php.ini-recommended
; and http://php.net/manual/en/security.php.
[–] cowlevel 14 hours ago
[–] bell-cot 14 hours ago
[–] cowlevel 14 hours ago
[–] bell-cot 12 hours ago
Maybe compare with https://github.com/php/php-src/blob/master/php.ini-developme..., too.
Then similar for your web server (Apache, nginx, whatever).
EDIT: About your "would've seemed adequate before this" - I dug up a copy of a PHP v5.2 php.ini file (2-ish decades ago). That file begins thus:
[–] cowlevel 12 hours ago