The Practical Linux Hardening Guide


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"Did you know all your doors were locked?" - Riddick (The Chronicles of Riddick)


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Created by trimstray and contributors

:collision: Work in progress, just a moment... First, I update a [Table Of Content](#table-of-content) and chapters. **** ## Table Of Contents - **[Contributing](#contributing)** - **[Pre install tasks](#pre-install-tasks)** * **[Hard disk encryption](#hard-disk-encryption)** + [Introduction](#information_source-introduction-1) + [Encrypt root filesystem](#eight_pointed_black_star-encrypt-root-filesystem) + [Encrypt /boot partition](#eight_pointed_black_star-encrypt-boot-partition) + [Swap partition](#eight_pointed_black_star-swap-partition) + [Summary checklist](#ballot_box_with_check-summary-checklist-1) - **[Post install tasks](#post-install-tasks)** * **[Bootloader configuration (grub)](#bootloader-configuration-grub)** + [Introduction](#information_source-introduction-2) + [Protect bootloader with password](#information_source-protect-bootloader-with-password) + [Protect bootloader config files](#information_source-protect-bootloader-config-files) + [Summary checklist](#ballot_box_with_check-summary-checklist-2) * **[Disk partitions](#disk-partitions)** + [Introduction](#information_source-introduction-3) + [Separate disk partitions](#eight_pointed_black_star-separate-disk-partitions) + [Mount options: nodev, noexec and nosuid](#eight_pointed_black_star-mount-options-nodev-noexec-and-nosuid) + [Secure /boot directory](#eight_pointed_black_star-secure-boot-directory) + [Secure /tmp and /var/tmp](#eight_pointed_black_star-secure-tmp-and-vartmp) + [Secure /dev/shm](#eight_pointed_black_star-secure-devshm) + [Secure /proc filesystem](#eight_pointed_black_star-secure-proc-filesystem) + [Swap partition](#eight_pointed_black_star-swap-partition-1) + [Disk quotas](#eight_pointed_black_star-disk-quotas) + [Summary checklist](#ballot_box_with_check-summary-checklist-3) * **[Keep system updated](#keep-system-updated)** * [Package management](#package-management) + [Automatic security updates](#automatic-security-updates) + [Remove packages with known issues](#remove-packages-with-known-issues) * [Netfilter ruleset](#netfilter-ruleset) * [TCP wrapper](#tcp-wrapper) * [Users and groups](#users-and-groups) + [Limit su access](#limit-su-access) + [Disable root account](#disable-root-account) + [Logins to system console](#logins-to-system-console) + [Disable shell accounts](#disable-shell-accounts) + [Strong password policy](#strong-password-policy) + [Password aging](#password-aging) + [Previous passwords](#previous-passwords) + [Login failures](#login-failures) + [Protect single user mode](#protect-single-user-mode) * [System path permissions](#system-path-permissions) + [World writable files](#world-writable-files) * [PAM module](#pam-module) * [Limits](#limits) * [Shadow passwords](#shadow-passwords) * [Linux kernel hardening](#linux-kernel-hardening) + [Kernel parameters](#kernel-parameters) + [Network security](#improve-network-security) + [System security](#improve-system-security) * [Remove unused modules](#remove-unused-modules) * [Secure shared memory](#secure-shared-memory) * [IRQ balance](#irq-balance) * [Disable compilers](#disable-compilers) * [Email notifications](#email-notifications) + [Rebooting the system](#rebooting-the-system) * [Backups](#backups) * [External devices](#external-devices) + [Disable USB usage](#disable-usb-usage) - **[Tools](#tools)** * [Logging and Auditing](#logging-and-auditing) + [Auditd](#auditd) + [Tiger](#tiger) + [Aide](#aide) + [Logwatch](#logwatch) * [Other](#other) + [Fail2ban](#fail2ban) + [PSAD](#psad) + [SELinux](#selinux) + [Entropy daemon](#entropy-daemon) + [Centralized authentication service](#centralized-authentication-service) * [Testing tools](#testing-tools) + [Lynis](#lynis) + [Chrootkit](#chrootkit) - **[Services](#services)** * [Disable all unnecessary services](#disable-all-unnecessary-services) + [Common unix print system](#eight_pointed_black_star-common-unix-print-system) + [Summary Checklits](#ballot_box_with_check-summary-checklist-4) * [System services](#system-services) + [OpenSSH](#openssh) + [NTP](#ntp) + [Cron](#cron) + [Anacron](#anacron) + [GnuPG 2](#gnupg2) + [Unattended key generation](#unattended-key-generation) * [DNS services](#dns-services) + [Bind9](#bind9) * [Mail services](#mail-services) + [Postfix](#postfix) * [Web services](#web-services) + [Nginx](#nginx) - [Files and directories permissions](#files-and-directories-permissions) - [Use HTTPS](#use-https) - [Enable HTTP2](#enable-http2) - [Diffie Hellman Ephemeral Parameter](#diffie-hellman-ephemeral-parameter) - [Separate domains](#separate-domains) - [Redirect all unencrypted traffic to HTTPS](#redirect-all-unencrypted-traffic-to-https) - [Enable HTTP Strict Transport Security](#enable-http-strict-transport-security) - [Security related headers](#security-related-headers) + [Apache](#apache) * [Databases](#databases) + [PostgreSQL](#postgresql) + [MySQL](#mysql) + [Redis](#redis) * [Queues](#queues) + [AMQP](#amqp) - **[Deployment](#deployment)** - **[Testing configuration](#testing-configuration)** - **[External resources](#external-resources)** ## Contributing If you find something which doesn't make sense, or one of these doesn't seem right, or something seems really stupid; please make a pull request or please add valid and well-reasoned opinions about your changes or comments. Before add pull request please see **[this](CONTRIBUTING.md)**. ## Pre install tasks ### Hard disk encryption #### :information_source: Introduction Disk encryption is focused on securing physical access, while relying on other parts of the system to provide things like network security and user-based access control. Most of the Linux distributions will allow you to encrypt your disks before installation. If you use an alternative installation method (e.g. from `debootstrap`) you can create an [encrypted disk manually](#disk-partitions). Before this you should to answer the following questions: - What part of filesystem do you want to encrypt? * only user data * user data and system data - How should `swap`, `/tmp` and other be taken care of? * disable or mount as ramdisk * encrypt (separately of as part of full) - How should encrypted parts of the disk be unlocked? * passphrase * key file - When should encrypted parts of the disk be unlocked? * before boot process * during boot process * mixed above or manually [Source](https://uchicago.service-now.com/it?id=kb_article&kb=KB06000398) #### :eight_pointed_black_star: Encrypt root filesystem Unlocked during boot, using passphrases or USB stick with keyfiles. #### :eight_pointed_black_star: Encrypt /boot partition - encrypting the whole disk without `/boot` partition but keeping it on a flash drive you carry at all times - using a checksum value of the boot sector - boot partition to detect it and change you passphrase This may not completely get rid of the attack vector described in this post as there is still part of the bootloader that isn't encrypted, but at least the grub stage2 and the kernel/ramdisk are encrypted and should make it much harder to attack. In addition, the `/boot` partition may be a weak point if you use encryption methods for the rest of the disk. Historically it has been necessary to leave `/boot` unencrypted because bootloaders didn't support decrypting block devices. However, there are some dangers to leaving the bootloader and ramdisks unencrypted. Before this you should to answer the following questions: - Where your `/boot` partition is stored? * the same place where stored `/` * separately partition * external flash drive The following recipe should be made after installing the system (however, these steps are included in this section to avoid mixing issues). [Source](https://security.stackexchange.com/questions/166075/encrypting-the-boot-partition-in-a-linux-system-can-protect-from-an-evil-maid-a) ###### Create copy of your /boot ```bash mkdir /mnt/boot mount --bind / /mnt/boot rsync -aAXv /boot/ /mnt/boot/ umount /mnt/boot ``` ###### Removed old /boot partition ```bash umount /boot sed -i -e '/\/boot/d' /etc/fstab ``` ###### Regenerate grub configuration ```bash # Debian like distributions grub-mkconfig > /boot/grub/grub.cfg # RedHat like distributions grub2-mkconfig > /boot/grub2/grub.cfg ``` ###### Enable `GRUB_ENABLE_CRYPTODISK` param ```bash echo GRUB_ENABLE_CRYPTODISK=y >> /etc/default/grub ``` ###### Reinstall grub ```bash # Debian like distributions grub-install /dev/sda # RedHat like distributions grub2-install /dev/sda ``` > More details can be found here (Bootloader configuration (grub) section): > - [Lock the boot directory](#eight_pointed_black_star-lock-the-boot-directory) #### :eight_pointed_black_star: Swap partition - swap area is not required to survive a reboot, therefore a new random encryption key can be chosen each time the swap area is activated - get the key from `/dev/urandom` because `/dev/random` maybe stalling your boot sequence #### :ballot_box_with_check: Summary checklist | Item | True | False | | :--- | :---: | :---: | | Encrypting the whole disk | :black_square_button: | :black_square_button: | | Usage passphrase or key file to disk unlocked | :black_square_button: | :black_square_button: | | Choosing a strong passphrase | :black_square_button: | :black_square_button: | | Encrypting the `/boot` partition | :black_square_button: | :black_square_button: | | Securing swap partition with `/dev/urandom` | :black_square_button: | :black_square_button: | | `swap` or `tmp` using an automatically generated per-session throwaway key | :black_square_button: | :black_square_button: | ## Post install tasks ### Bootloader configuration (grub) #### :information_source: Introduction Protection for the boot loader can prevent unauthorized users who have physical access to systems, e.g. attaining root privileges through single user mode. Basically when you want to prohibit unauthorized reconfiguring of your system, otherwise anybody could load anything on it. #### :eight_pointed_black_star: Protect bootloader with password You can set password for the bootloader for prevents users from entering single user mode, changing settings at boot time, access to the bootloader console, reset the root password, if there is no password for GRUB-menu or access to non-secure operating systems. ###### Generate password hash ```bash # Debian like distributions grub-mkpasswd-pbkdf2 # RedHat like distributions grub2-mkpasswd-pbkdf2 ``` ###### Updated grub configuration ```bash cat > /etc/grub.d/01_hash << __EOF__ set superusers="user" password_pbkdf2 user grub.pbkdf2.sha512. # rest of your password hash __EOF__ ``` And regenerate grub configuration: ```bash # Debian like distributions grub-mkconfig > /boot/grub/grub.cfg # RedHat like distributions grub2-mkconfig > /boot/grub2/grub.cfg ``` #### :eight_pointed_black_star: Protect bootloader config files Set the owner and group of `/etc/grub.conf` to the root user: ```bash chown root:root /etc/grub.conf ``` or ```bash chown -R root:root /etc/grub.d ``` Set permission on the `/etc/grub.conf` or `/etc/grub.d` file to read and write for root only: ```bash chmod og-rwx /etc/grub.conf ``` or ```bash chmod -R og-rwx /etc/grub.d ``` #### :ballot_box_with_check: Summary checklist | Item | True | False | | :--- | :---: | :---: | | Set password for the bootloader | :black_square_button: | :black_square_button: | ### Disk partitions #### :information_source: Introduction Critical file systems should be separated into different partitions in ways that make your system a better and more secure. #### :eight_pointed_black_star: Separate disk partitions Make sure the following filesystems are mounted on separate partitions: - `/boot` - `/tmp` - `/var` - `/var/log` Additionally, depending on the purpose of the server, you should consider separating the following partitions: - `/usr` - `/home` - `/var/www` You should also consider separating these partitions: - `/var/tmp` - `/var/log/audit` #### :eight_pointed_black_star: Mount options: nodev, nosuid and noexec For more security-focused situations is as follows: - `nodev` - specifies that the filesystem cannot contain special devices: This is a security precaution. You don't want a user world-accessible filesystem like this to have the potential for the creation of character devices or access to random device hardware - `nosuid` - specifies that the filesystem cannot contain set userid files. Preventing setuid binaries on a world-writable filesystem makes sense because there's a risk of root escalation or other awfulness there - `noexec` - this param might be useful for a partition that contains no binaries, like **/var**, or contains binaries you do not want to execute on your system (from partitions with `noexec`), or that cannot even be executed on your system #### :eight_pointed_black_star: Secure /boot directory The boot directory contains important files related to the Linux kernel, so you need to make sure that this directory is locked down to read-only permissions. Add **ro** option and `nodev`, `nosuid` and `noexec` to `/etc/fstab` for **/boot** entry: ```bash LABEL=/boot /boot ext2 defaults,ro,nodev,nosuid,noexec 1 2 ``` > When updating the kernel you will have to move the flag to `rw`: > ```bash > mount -o remount,defaults,rw /boot > ``` #### :eight_pointed_black_star: Secure /tmp and /var/tmp On Linux systems, the **/tmp** and **/var/tmp** locations are world-writable. Several daemons/applications use the **/tmp** or **/var/tmp** directories to temporarily store data, log information, or to share information between their sub-components. However, due to the shared nature of these directories, several attacks are possible, including: - Leaks of confidential data via secrets in file names - Race-condition attacks (TOCTOU) on the integrity of processes and data - Denial-of-Service (DoS) attacks based on race conditions and pre-allocating file/directory names As a rule of thumb, malicious applications usually write to **/tmp** and then attempt to run whatever was written. A way to prevent this is to mount **/tmp** on a separate partition with the options `nodev`, `nosuid` and `noexec` enabled. This will deny binary execution from **/tmp**, disable any binary to be suid root, and disable any block devices from being created. **The first possible scenario is create symlink** ```bash mv /var/tmp /var/tmp.old ln -s /tmp /var/tmp cp -prf /var/tmp.old/* /tmp && rm -fr /var/tmp.old ``` and set properly mount params: ```bash UUID=<...> /tmp ext4 defaults,nodev,nosuid,noexec 1 2 ``` **The second scenario is a bind mount** The storage location **/var/tmp** should be bind mounted to **/tmp**, as having multiple locations for temporary storage is not required: ```bash /tmp /var/tmp none rw,nodev,nosuid,noexec,bind 0 0 ``` **The third scenario is setting up polyinstantiated directories** Create new directories: ```bash mkdir --mode 000 /tmp-inst mkdir --mode 000 /var/tmp/tmp-inst ``` Edit `/etc/security/namespace.conf`: ```bash /tmp /tmp-inst/ level root,adm /var/tmp /var/tmp/tmp-inst/ level root,adm ``` Set correct **SELinux** context: ```bash setsebool polyinstantiation_enabled=1 chcon --reference=/tmp /tmp-inst chcon --reference=/var/tmp/ /var/tmp/tmp-inst ``` And set `nodev`, `nosuid` and `noexec` mount options in `/etc/fstab`. > Alternative for **polyinstantiated directories** is **PrivateTmp** feature available from **systemd**. For more information please see: [New Red Hat Enterprise Linux 7 Security Feature: PrivateTmp](https://access.redhat.com/blogs/766093/posts/1976243). #### :eight_pointed_black_star: Secure /dev/shm `/dev/shm` is a temporary file storage filesystem, i.e. **tmpfs**, that uses RAM for the backing store. One of the major security issue with the `/dev/shm` is anyone can upload and execute files inside the `/dev/shm` similar to the `/tmp` partition. Further the size should be limited to avoid an attacker filling up this mountpoint to the point where applications could be affected. (normally it allows 20% or more of RAM to be used). The sticky bit should be set like for any world writeable directory. For applies to shared memory `/dev/shm` mount params: ```bash tmpfs /dev/shm tmpfs rw,nodev,nosuid,noexec,size=1024M,mode=1777 0 0 ``` > You can also create a group named 'shm' and put application users for SHM-using applications in there. Then the access can be completely be restricted as such: ```bash tmpfs /dev/shm tmpfs rw,nodev,nosuid,noexec,size=1024M,mode=1770,uid=root,gid=shm 0 0 ``` #### :eight_pointed_black_star: Secure /proc filesystem The proc pseudo-filesystem `/proc` should be mounted with `hidepid`. When setting `hidepid` to **2**, directories entries in `/proc` will hidden. ```bash proc /proc proc defaults,hidepid=2 0 0 ``` > Some of the services/programs operate incorrectly when the `hidepid` parameter is set, e.g. Nagios checks. #### :eight_pointed_black_star: Swap partition #### :eight_pointed_black_star: Disk quotas #### :ballot_box_with_check: Summary checklist | Item | True | False | | :--- | :---: | :---: | | Separate base partition scheme: `/boot`, `/tmp`, `/var`, `/var/log` | :black_square_button: | :black_square_button: | | Separate `/usr` partition | :black_square_button: | :black_square_button: | | Separate `/home` partition | :black_square_button: | :black_square_button: | | Separate `/var/www` partition | :black_square_button: | :black_square_button: | | Separate `/var/tmp` partition | :black_square_button: | :black_square_button: | | Separate `/var/audit` partition | :black_square_button: | :black_square_button: | | Secure `/boot` directory with `ro`, `nodev`, `nosuid`, `noexec` options | :black_square_button: | :black_square_button: | | Secure `/tmp` and `/var/tmp` directory with `nodev`, `nosuid`, `noexec` options | :black_square_button: | :black_square_button: | | Create symlink for `/var/tmp` in `/tmp` | :black_square_button: | :black_square_button: | | Setting up bind-mount `/var/tmp` to `/tmp` | :black_square_button: | :black_square_button: | | Setting up polyinstantiated directories for `/tmp` and `/var/tmp` | :black_square_button: | :black_square_button: | | Secure `/dev/shm` directory with `nodev`, `nosuid`, `noexec` options | :black_square_button: | :black_square_button: | | Secure `/proc` filesystem with `hidepid=2` option | :black_square_button: | :black_square_button: | ## Services ### Disable all unnecessary services The action in this section provide guidance on some of unwanted applications and services which you might not needed but they are installed by default during OS installation and unknowingly start eating your system resources and also threats to the system security. If unused services is not enabled then it cannot be exploited. #### :eight_pointed_black_star: Common Unix Print System The Common Unix Print System (CUPS) provides the ability to print to both local and network printers. If the system does not need to accept print jobs from other systems, it's recommended that CUPS be disabled to reduce the potential attack. Run the following command to verify cups is not enabled: ```bash # systemctl is-enabled cups disabled ``` Run the following command to disable cups: ```bash # systemctl disable cups ``` [Source](http://www.cups.org) ### Web services ### Nginx Nginx is an HTTP and reverse proxy server, a mail proxy server, and a generic TCP/UDP proxy server, originally written by [Igor Sysoev](http://sysoev.ru/en/). It's used worldwide, and is one of best tools at what it does. Default configuration that comes with it, however, is not very security oriented, and it requires some work to set it up properly. That's what this section aims to help you with. [Source](https://nginx.org/en/) #### :eight_pointed_black_star: Files and directories permissions Usually setting directories permissions to `0755` and file permissions to `0644` is a good practise. `0755` permissions for directories allows nginx user to access files in the folder, however you don't want to grant same type of permissions to a file, as granting execution permissions to a file is not a good idea, especially on a publicly exposed server. Script for setting all directories permissions to `0755` (here we assume that webserver directory path is `/var/www/html`): ```bash find /var/www/html -type d -exec chmod 755 {} \; ``` Script for setting all files permissions to `0644`: ```bash find /var/www/html -type f -exec chmod 644 {} \; ``` Whatever you do, never grant `0777` permissions to files, nor folders. #### :eight_pointed_black_star: Use HTTPS In this day and age, with services like [Let's Encrypt](https://letsencrypt.org/), there's no excuse not to use HTTPS for your website. This example configuration also includes stronger cihper suite, ssl session adjustments, HSTS header, stronger DHE parameter, and OSCP Stapling. **Example of a config with HTTP to HTTPS redirection:** ``` server { listen 80 default_server; listen [::]:80 default_server; server_name example.com; return 301 https://$host$request_uri; server_tokens off; } server { listen 443 ssl default_server; listen [::]:443 ssl; server_name example.com; server_tokens off; ssl on; ssl_certificate /etc/nginx/ssl/ssl-bundle.crt; ssl_certificate_key /etc/nginx/ssl/cert.key; ssl_session_timeout 1d; ssl_session_cache shared:SSL:50m; ssl_session_tickets off; ssl_protocols TLSv1.2; ssl_ciphers 'ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES256-SHA:ECDHE-ECDSA-DES-CBC3-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA:!DSS'; ssl_prefer_server_ciphers on; ssl_stapling on; ssl_stapling_verify on; ssl_dhparam /etc/nginx/ssl/dhparam-4096.pem; } ``` [Source](https://mozilla.github.io/server-side-tls/ssl-config-generator/) #### :eight_pointed_black_star: Enable HTTP/2 HTTP/2 is a replacement for how HTTP is expressed “on the wire.” It is not a ground-up rewrite of the protocol; HTTP methods, status codes and semantics are the same, and it should be possible to use the same APIs as HTTP/1.x (possibly with some small additions) to represent the protocol. [Source](https://http2.github.io/) **Differences between HTTP/2 and HTTP/1.1:** At a high level, HTTP/2: [Source](https://http2.github.io/faq/#what-are-the-key-differences-to-http1x) **Example config that enables HTTP/2:** ``` server { listen 80 default_server; listen [::]:80 default_server; server_name example.com; return 301 https://$host$request_uri; server_tokens off; } server { listen 443 ssl http2 default_server; listen [::]:443 ssl http2; server_name example.com; server_tokens off; ssl on; ssl_certificate /etc/nginx/ssl/ssl-bundle.crt; ssl_certificate_key /etc/nginx/ssl/cert.key; } ``` #### :eight_pointed_black_star: Separate domains In case you have more than one website you'd like to serve from your server, nginx allows you to that. In this example we'll have 2 different websites, with 2 different domains, served from same virtual machine. **Example config that allows you to serve two websites with two different domains:** ``` server { listen 80; listen [::]:80; server_name first-example.com; root /var/www/html/website1; index index.html; server_tokens off; location / { try_files $uri $uri/ =404; } } server { listen 80; listen [::]:80; server_name second-example.com; root /var/www/html/website2; index index.html; server_tokens off; location / { try_files $uri $uri/ =404; } } ``` #### :eight_pointed_black_star: Redirect all unencrypted traffic to HTTPS This config entry is responsible for permanently redirecting all HTTP traffic to HTTPS. It will redirect all visitors that try to access website through HTTP on port 80, to HTTPS on port 443: `return 301 https://$host$request_uri;` **Example config:** ``` server { listen 80 default_server; listen [::]:80 default_server; server_name example.com; return 301 https://$host$request_uri; server_tokens off; } server { listen 443 ssl http2 default_server; listen [::]:443 ssl http2; server_name example.com; server_tokens off; ssl on; ssl_certificate /etc/nginx/ssl/ssl-bundle.crt; ssl_certificate_key /etc/nginx/ssl/cert.key; } ``` #### :eight_pointed_black_star: Enable HTTP Strict Transport Security **What is HSTS?** HTTPS (HTTP encrypted with SSL or TLS) is an essential part of the measures to secure traffic to a website, making it very difficult for an attacker to intercept, modify, or fake traffic between a user and the website. When a user enters a web domain manually (providing the domain name without the http:// or https:// prefix) or follows a plain http:// link, the first request to the website is sent unencrypted, using plain HTTP. Most secured websites immediately send back a redirect to upgrade the user to an HTTPS connection, but a well‑placed attacker can mount a man‑in‑the‑middle (MITM) attack to intercept the initial HTTP request and can control the user’s session from then on. [Source](https://www.nginx.com/blog/http-strict-transport-security-hsts-and-nginx/) Config entry : ```bash add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always; ``` **Example config** ```bash server { listen 80 default_server; listen [::]:80 default_server; server_name example.com; return 301 https://$host$request_uri; server_tokens off; } server { listen 443 ssl http2 default_server; listen [::]:443 ssl http2; server_name example.com; server_tokens off; ssl on; ssl_certificate /etc/nginx/ssl/ssl-bundle.crt; ssl_certificate_key /etc/nginx/ssl/cert.key; add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always; } ``` #### :eight_pointed_black_star: Diffie Hellman Ephemeral Parameter All versions of nginx as of 1.4.4 rely on OpenSSL for input parameters to Diffie-Hellman (DH). Unfortunately, this means that Ephemeral Diffie-Hellman (DHE) will use OpenSSL's defaults, which include a 1024-bit key for the key-exchange. This example aims to generate stronger DHE parameter: ```bash cd /etc/nginx/ssl/ openssl dhparam -out dhparam-4096.pem 4096 ``` Then add it to your nginx config with this config entry: ```bash ssl_dhparam /etc/nginx/ssl/dhparam-4096.pem; ``` [Source](https://raymii.org/s/tutorials/Strong_SSL_Security_On_nginx.html) #### :eight_pointed_black_star: Security related headers _Cross-site scripting (XSS) protection:_ Helps with preventing XSS attacks, it's enabling cross-site scripting filter built into modern browsers. ```bash add_header x-xss-protection "1; mode=block" always; ``` _X-Frame-Options:_ Prevents iframe loading from different websites: ```bash add_header x-frame-options "SAMEORIGIN" always; ``` _X-Content-Type-Options:_ It helps reducing drive-by downloads: ```bash add_header X-Content-Type-Options "nosniff" always; ``` _HTTP Strict Transport Security (HSTS):_ When a browser sees this header from an HTTPS website, it “learns” that this domain must only be accessed using HTTPS (SSL or TLS). It caches this information for the max-age period (typically 31,536,000 seconds, equal to about 1 year). ```bash add_header Strict-Transport-Security "max-age=31536000; includeSubDomains" always; ``` [Source 1](https://www.nginx.com/blog/http-strict-transport-security-hsts-and-nginx/) [Source 2](https://www.owasp.org/index.php/OWASP_Secure_Headers_Project)