Found it, you were right, thanks. CVE-2026-115560, no patch yet. The good news is it needs an unusual setup: an app that sets session.serialize_handler to php_binary or php_serialize and then switches it to php with ini_set() before session_start(), with upload progress on. PHP rates it unlikely and will fix it in a regular release. Meanwhile the same mitigation as before: session.upload_progress.enabled=0. No exploitation reported.
https://www.bleepingcomputer.com/news/security/php-shares-mitigation-for-new-and-unpatched-rce-vulnerability/
