Ondřej Surý has finally released PHP 7.2.0 Beta 3 packages for Debian GNU/Linux 8 (oldstable)

What's new in PHP 7.2.0 Beta 3:

- Core:
. Fixed bug #75063 (Main CWD initialized with wrong codepage). (Anatol)

- Date:
. Fixed bug #75002 (Null Pointer Dereference in timelib_time_clone). (Derick)

- FTP:
. Added ftp_append() function. (blar)

- Mbstring:
. Fixed bug #75001 (Wrong reflection on mb_eregi_replace). (Fabien
Villepinte)

- SQLite3:
. Updated to SQLite 3.20.0. (cmb)

- SPL:
. Fixed bug #75049 (spl_autoload_unregister can't handle
spl_autoload_functions results). (Laruence)
. Added spl_object_id(). (Tyson Andre)

- Standard:
. Fixed bug #75075 (unpack with X* causes infinity loop). (Laruence)
. Fixed bug #74103 (heap-use-after-free when unserializing invalid array
size). (Nikita)
. Fixed bug #75054 (A Denial of Service Vulnerability was found when
performing deserialization). (Nikita)

- WDDX:
. Fixed bug #73793 (WDDX uses wrong decimal seperator). (cmb)

- XMLRPC:
. Fixed bug #74975 (Incorrect xmlrpc serialization for classes with declared
properties). (blar)

To add the deb.sury.org PHP repository to your Debian installation, run as root:

apt-get install apt-transport-https lsb-release ca-certificates
wget -O /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg
sh -c 'echo "deb https://packages.sury.org/php/ $(lsb_release -sc) main" > /etc/apt/sources.list.d/php.list'
apt-get update

To install PHP 7.2 with MySQL/MariaDB and php-fpm support:

apt-get install php7.2-cgi php7.2-gd php7.2-curl php7.2-imap php7.2-sqlite3 php7.2-mysql php7.2-tidy php7.2-pspell php7.2-recode php7.2-xml php7.2-intl php7.2-enchant php7.2-gmp php7.2-mbstring php7.2-soap php7.2-xmlrpc php7.2-zip php7.2-fpm

Please note that the mcrypt package is no longer available after the support has been removed from PHP 7.2