PHP

Warning:

These instructions were only tested on Debian. It will probably work for other Linux distributions, but you might need to adapt the provided instructions.

Warning:

This page is a work in progress and is not completed. Important informations might be missing or wrong.

Prerequisite

To use this guide, you will need Nginx installed and configured.

Installation

Debian Jessie

# apt install php5-cli php5-fpm php5-apcu

Debian Stretch

# apt install php7.0-cli php7.0-fpm php7.0-apcu

Configuration

Common configuration

In Debian, the different flavour of PHP have their own configuration file. This allow fine grained configuration but makes it harder to have common behaviour.

Let’s create a common file read by all PHP interpreters.

Debian Jessie

# echo -e '; Commmon configuration for all PHP interpreters\n; priority=99\n' > /etc/php5/mods-available/local-common.ini
# php5enmod local-common

Unless specified, all the settings bellow should go to /etc/php5/mods-available/local-common.ini

Debian Stretch

# echo -e '; Commmon configuration for all PHP interpreters\n; priority=99\n' > /etc/php/7.0/mods-available/local-common.ini
# phpenmod -v 7.0 local-common

Unless specified, all the settings bellow should go to /etc/php/7.0/mods-available/local-common.ini

Integrate with Nginx

Debian Jessie

Create file /etc/nginx/conf.d/php5.conf

upstream php5 {
    server unix:/var/run/php5-fpm.sock;
}

Debian Stretch

Create file /etc/nginx/conf.d/php7.0.conf

upstream php7 {
    server unix:/var/run/php7.0-fpm.sock;
}

Security

PHP is known to have a particularly poor track record in term of security. Although things are improving, it is recommended to harden you installation.

Hide PHP

It is generally a bad idea to give information on the technologies used by your system. This setting make sure that PHP is not exposed.

; Name of the sessionid cookie. Hide PHP and get a smaller cookie
session.name = sid
; Don't add script name in emails
mail.add_x_header = 0

Session IDs

By default PHP session IDs are not very random. Let's get some more entropy

; By default, PHP session IDs are not very random
; http://samy.pl/phpwn/ reduce session entropy down to 20 bits
; The settings bellow uses 256 bits of entropy from /dev/urandom
session.entropy_length = 32
; Default is md5
session.hash_function = sha256
; Not security related. Make the session ID cookie a bit shorter
session.hash_bits_per_character = 6

Prevent session fixation attacks

; Don't allow client to choose their session id
session.use_strict_mode = 1
; Hide session cookie from JavaScript
session.cookie_httponly = 1
; Make session cookie work only with HTTPS
; Warning: it might break you application if you don't use HTTPS
session.cookie_secure = 1

Limit File Access

By default, PHP allow scripts to read any file on the machine including sensible files like /etc/passwd. The setting bellow limit that. Of course when new sites are added, the list of folder need to be extended.

; Column separated list of folder to allow inclusion from.
; Eg. "/usr/share/php/:/usr/share/phpmyadmin/"
open_basedir = "/usr/share/php/"

Limit access to POST data

This setting only apply to Debian 8 (Jessie) and bellow

; The preferred method for accessing raw POST data is php://input, and $HTTP_RAW_POST_DATA is deprecated in PHP 5.6.0 onwards.
; This feature is removed in PHP7
always_populate_raw_post_data = -1;