Users with superuser privileges – sudo and su on RHEL 8

Sudo and su are two powerful utilities on linux operating system that enables one to manipulate who is performing actions on the filesystem and with which privileges .

The main difference between those two tools is that if administrator uses su - username then he should provide the user password in order to switch to the end user rights. On the other hand with sudo command the administrator should use its own password in order to validate with the system that he wants to run as a superuser the command su - .

As a result by using sudo su - x you dont have to specify the end user password but your own password.

Another way you can authorize your self as superuser is with sudo -i so you do not have to provide the password of root in the system.

The sudo command is very powerful and useful in the linux systems because for security purposes many times you could find root user deactivated and each user has its own credentials and rights. Also actions performed with sudo commands are logged in the operating system.

The most important prerequisite in order to use sudo command in Red Hat or Centos Linux is to be a member of the wheel group. You can give a specific user sudo rights with the following:

Create a new file under /etc/sudoers.d/USERNAME

touch /etc/sudoers.d/operator

and then vi the operator file and add the following line:

operator ALL=(ALL) ALL

using sudo with a user that does not have admin rights.
using sudo after creating the necessary file under sudoers.d

The ultimate Guide of Security – Infrastructure Web application Hardening

This guide is written in order to help the IT Security Administrators secure their Infrastructure (VM in the cloud or something equivalent) that host web applications. It encloses knowledge that has been gained from multiple penetrations test from different vendors in projects that I have participated. It cannot protect you 100% but is a good and detailed way to start your security hardening.

Table of contents:

  • OS patching
  • Strong passwords and permissions
  • SSL Certificate
  • Install fail2ban
  • Set up firewall
  • Limit ssh access
  • PHP Hardening
  • Apache Hardening

OS patching:
Keep always your OS ( Red Hat Linux or equivalent) up to date with the latest security updates and patches. As a result before starting your installations perform an OS update. It is very important also to keep your Apache and PHP packages patched.

Strong passwords and permissions:
Create strong passwords for your users and add users with separate directories and permissions. Each user should have its own directory to manipulate files and should not have root access. For example if user X should be the application owner, then he should have permissions only to write/upload files in /var/www/application folder and no root permissions.

SSL Certificate:
Install a valid SSL Certificate and redirect all http traffic to https. You can view my blog post on how to install your apache SSL certificate from here. Redirection can be implemented by adding the appropriate rule in your .htaccess file.

Install fail2ban:
Fail2Ban scans log files like /var/log/auth.log and bans IP addresses conducting too many failed login attempts. You can find it from Github and configure it appropriately.

Set up firewall:
You should consider enabling a firewall for your infrastructure like Cloudflare that enables WAF/DDOS protection actions. You could also enable the build in Linux firewall and set up rules through iptables.

Limit ssh access:
Limit IP addresses that could access your infrastructure server. You could do that by disabling all from /etc/hosts.deny and allow only the IP addresses that you will use in /etc/hosts.allow . As a result you should

/etc/hosts.deny:
sshd : ALL

/etc/hosts.allow:
sshd : YOUR_IPS/24

PHP Hardening:
open_basedir, if set, limits all file operations to the defined directory and below. When a script tries to access the filesystem for example using fsockopen() the location of the file is checked. If the file is outside the defined directory PHP will refuse access.
Set openbasedir to your site directory. For example if your web application is a drupal installed in the directory /var/www/drupal then your openbasedir should be set to include your app directory and every other directory that you want (see below example).

open_basedir = "/home/X/:/var/www/drupal/:/tmp/"

Also you should consider disabling some php functions for security reasons like the below.

disable_functions = phpinfo,exec,shell_exec,passthru,system,proc_open,popen,curl_exec,curl_multi_exec,parse_ini_file,show_source,proc_close,symlink,apache_getenv,apache_get_modules,apache_get_version,apache_lookup_uri,apache_note,apache_request_headers,apache_reset_timeout,apache_response_headers,apache_setenv,closelog,curl_exec,curl_multi_exec,debugger_off,debugger_on,define_syslog_var,define_syslog_variables,diskfreespace,disk_free_space,dl,escapeshellarg,escapeshellcmd,exec,ftok,ftp_connect,ftp_exec,ftp_get,ftp_login,ftp_nb_fput,ftp_put,ftp_raw,ftp_rawlist,getmypid,getmyuid,highlight_file,ignore_user_abord,ini_alter,ini_get_all,ini_restore,leak,limit,link,listen,mysql_list_dbs,openlog,parse_ini_file,passthru,pclose,pcntl_exec,pg_host,php_uname,popen,posix_access,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_getpwnam,posix_getpwuid,posix_getrlimit,posix_getsid,posix_getuid,posix_isatty,posix_kill,posix_mkfifo,posix_mknod,posix_setegid,posix_seteuid,posix_setgid,posix_setp,posix_setpgid,posix_setsid,posix_setuid,posix_times,posix_ttyname,posix_uname,proc_close,proc_get_status,proc_nice,proc_open,proc_terminate,readfile,readlink,safe_dir,satty,scandir,set_time,set_time_limit,shell_exec,show_source,socket_accept,socket_bind,socket_clear_error,socket_close,socket_connect,source,symlink,syslog,system,tmpfile,virtual

Disable allow_url_include and allow_url_fopen

allow_url_fopen=Off
allow_url_include=Off

The previous described actions should be applied on /etc/php.ini file.

Some of them may disable your web application behavior so you should check if you need them.

Apache Hardening:


Disable content or MIME sniffing:

Header set X-Content-Type-Options: "nosniff"

Defense from Clickjacking attack:

Header set X-Frame-Options: "sameorigin"

Set Strict-Transport-Security header settings configured for a timespan of 2 years:

Header set Strict-Transport-Security "max-age=63072000; includeSubDomains;"

Add X-XSS-Protection header to prevent some level of XSS:

Header set X-XSS-Protection "1; mode=block"

Add Referrer-Policy header to your webserver:

Header always set Referrer-Policy "same-origin"

Deny TRACE/TRACK requests:

RewriteEngine On
RewriteCond %{REQUEST_METHOD} ^(TRACE|TRACK)
RewriteRule .* - [F]

Hide Apache Information:

ServerSignature Off
ServerTokens Prod

Of course there are a lot more things that could be applied for your infrastructure hardening per case. The system Administrator should always be up to date with the security standards and discoveries in order to eliminate risks from malicious unauthorized access.