10 Steps for Securing a PHP Application

Hello PHP developers. In this article I provide concrete steps to improve the security of PHP applications by focusing on PHP configuration itself, without covering SQL injection, HTTPS, or other non‑PHP topics.

I illustrate the changes using bash lines from my docker-entrypoint.sh script, but the same adjustments apply to non‑Docker environments.

Sessions

Use a longer Session ID length

Increasing the session ID length makes brute‑force or side‑channel guessing harder; valid lengths range from 22 to 256 characters, with the default of 32.

sed -i -e "s/session.sid_length = 26/session.sid_length = 42/" /etc/php7/php.ini

Use a custom session save path with restricted permissions

Only nginx/php need access to sessions, so place them in a dedicated folder with limited rights.

sed -i -e "s:;session.save_path = \"/tmp\":session.save_path = \"/sessions\":" /etc/php7/php.ini
mkdir -p /sessions
chown nginx:nginx /sessions
chmod 700 /sessions

If you use Redis for sessions, this step can be skipped.

Secure session cookies

Enable session.cookie_httponly to block JavaScript access, and set session.cookie_secure to prevent transmission over plain HTTP. Also enable session.cookie_samesite (available in recent PHP/browser versions) to mitigate cross‑site attacks.

sed -i -e "s/session.cookie_httponly.*/session.cookie_httponly = true/" /etc/php7/php.ini
sed -i -e "s/;session.cookie_secure.*/session.cookie_secure = true/" /etc/php7/php.ini

Enable strict mode so that an attacker‑initialized session ID cannot be used.

sed -i -e "s/session.use_strict_mode.*/session.use_strict_mode = true/" /etc/php7/php.ini

Set session.cookie_lifetime to 0 so sessions expire when the browser closes.

sed -i -e "s/session.cookie_lifetime.*/session.cookie_lifetime = 0/" /etc/php7/php.ini

Open_basedir

The open_basedir directive limits the file system paths PHP can access.

sed -i -e "s#;open_basedir =#open_basedir = /elabftw/:/tmp/:/usr/bin/unzip#" /etc/php7/php.ini

Here /elabftw holds the source PHP files; /tmp is included for reasons specific to the environment.

Disable risky functions

Disabling functions such as shell_exec can prevent uploaded web shells from executing.

sed -i -e "s/disable_functions =/disable_functions = php_uname, getmyuid, getmypid, passthru, leak, listen, diskfreespace, tmpfile, link, ignore_user_abort, shell_exec, dl, system, highlight_file, source, show_source, fpaththru, virtual, posix_ctermid, posix_getcwd, posix_getegid, posix_geteuid, posix_getgid, posix_getgrgid, posix_getgrnam, posix_getgroups, posix_getlogin, posix_getpgid, posix_getpgrp, posix_getpid, posix_getppid, posix_getsid, posix_getuid, posix_isatty, posix_kill, posix_mkfifo, posix_setegid, posix_seteuid, posix_setgid, posix_setpgid, posix_setsid, posix_setuid, posix_times, posix_ttyname, posix_uname, phpinfo/" /etc/php7/php.ini

Disable allow_url_fopen

This option is dangerous; turn it off.

sed -i -e "s/allow_url_fopen = On/allow_url_fopen = Off/" /etc/php7/php.ini

Disable cgi.fix_pathinfo

Prevent non‑PHP files from being executed as PHP.

sed -i -e "s/;cgi.fix_pathinfo=1/cgi.fix_pathinfo=0/g" /etc/php7/php.ini

Hide PHP version

Turn off exposure of the PHP version.

sed -i -e "s/expose_php = On/expose_php = Off/g" /etc/php7/php.ini

That’s it. I hope you find these configuration tweaks useful and improve your PHP setup. If I missed anything important, please let me know in the comments.