An embargoed security issue in PHP leaked and it is extremely serious: all versions >5.4 are affected. No patches are available yet.
I highly recommend shutting down any PHP services until the patch is available—that's how serious this issue is.
Edit: Patches are available! Patch ASAP!!
Upstream: https://www.php.net/archive/2026.php#2026-10-21-5
Debian: https://security-tracker.debian.org/tracker/CVE-2026-109619
Ubuntu: https://ubuntu.com/security/notices/USN-8948-1
Fedora: https://bugzilla.redhat.com/show_bug.cgi?id=2556842
Fix does not yet appear to be available in RHEL: https://access.redhat.com/security/cve/cve-2026-109618
To mitigate, Apache HTTPD users can run
a2dismod php8.2 # any version
a2dissite <affected website configs>
systemctl restart apache2
https://cert.europa.eu/publications/security-advisories/2026-018/