Writeups from the various researchers who discovered the vulnerabilities:
Wiz: https://www.wiz.io/blog/php2shell-php-rce
Calif: https://calif.io/php2shell/
OpenAI: https://openai.com/index/coordinated-disclosure-of-critical-vulnerabilities/
wiz.ioPHP2Shell: AI uncovers critical RCE vulnerabilities affecting 70% of the Internet | Wiz BlogCore PHP engine flaws enable remote code execution and Heartbleed-style memory disclosure across the web.