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zen-rails-security-checklist

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Checklist of security precautions for Ruby on Rails applications.

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# Zen Rails Security Checklist

## Summary
This document provides a not necessarily comprehensive list of security measures
to be implemented when developing a Ruby on Rails application. It is designed to
serve as a quick reference and minimize vulnerabilities caused by developer
forgetfulness. It does not replace developer training on secure coding
principles and how they can be applied.

Describing how each security vulnerability works is outside the scope of this
document. Links to external resources containing further information are
provided in the corresponding sections of the checklist. Please apply only the
suggestions you thoroughly understand.

Please keep in mind that security is a moving target. New vulnerabilities and
attack vectors are discovered every day. We suggest you try to keep up to date,
for instance, by subscribing to security mailing lists related to the software
and libraries you are using.

This checklist is meant to be a community-driven resource. Your 
[contributions](#contributing) are welcome!

**Disclaimer**: This document does not cover all possible security 
vulnerabilities. The authors do not take any legal responsibility for the 
accuracy or completeness of the information herein.

## Supported Rails Versions
This document focuses on Rails 4 and 5. Vulnerabilities that were present in 
earlier versions and fixed in Rails 4 are not included.

## Table of Contents

- [The Checklist](#the-checklist)
    - [Injection](#injection)
    - [Authentication](#authentication)
    - [Sessions & Cookies](#sessions--cookies)
    - [Cross-Site Scripting (XSS)](#cross-site-scripting-xss)
        - [Handling User Input](#handling-user-input)
        - [Output Escaping & Sanitization](#output-escaping--sanitization)
        - [XSS protection in HAML templates](#xss-protection-in-haml-templates)
        - [Content Security Policy (CSP)](#content-security-policy-csp)
    - [Insecure Direct Object Reference](#insecure-direct-object-reference)
    - [HTTP & TLS](#http--tls)
        - [Security-related headers](#security-related-headers)
    - [Memcached Security](#memcached-security)
    - [Authorization (Pundit)](#authorization-pundit)
    - [Files](#files)
        - [File Uploads](#file-uploads)
        - [File Downloads](#file-downloads)
    - [Cross-Site Request Forgery (CSRF)](#cross-site-request-forgery-csrf)
    - [Cross Origin Resource Sharing (CORS)](#cross-origin-resource-sharing-cors)
    - [Sensitive Data Exposure](#sensitive-data-exposure)
        - [Credentials](#credentials)
    - [Routing, Template Selection, and Redirection](#routing-template-selection-and-redirection)
    - [Third-party Software](#third-party-software)
    - [Security Tools](#security-tools)
    - [Testing](#testing)
    - [Others](#others)
- [Details and Code Samples](#details-and-code-samples)
    - [Command Injection example](#command-injection-example)
    - [Password validation regex](#password-validation-regex)
    - [Pundit: ensure all actions are authorized](#pundit-ensure-all-actions-are-authorized)
    - [Pundit: only display appropriate records in select boxes](#pundit-only-display-appropriate-records-in-select-boxes)
    - [rack-cors configuration](#rack-cors-configuration)
    - [Convert filter_parameters into a whitelist](#convert-filter_parameters-into-a-whitelist)
    - [Throttling Requests](#throttling-requests)
    - [HAML: XSS protection](#haml-xss-protection)
- [Authors](#authors)
- [Contributing](#contributing)
- [TODO](#todo)
- [References and Further Reading](#references-and-further-reading)
- [License](#license)

Table of contents generated by [DocToc](https://github.com/thlorenz/doctoc).

## The Checklist

#### Injection 
Injection attacks are #1 at the [OWASP Top10](https://www.owasp.org/index.php/Top_10_2013-Top_10). 
- [ ] Don’t use standard Ruby interpolation (`#{foo}`) to insert user inputted
strings into ActiveRecord or raw SQL queries. Use the `?` character, named bind
variables or the [ActiveRecord::Sanitization
methods](http://api.rubyonrails.org/classes/ActiveRecord/Sanitization/ClassMethods.html#method-i-sanitize_conditions)
to sanitize user input used in DB queries. *Mitigates SQL injection attacks.*
- [ ] Don't pass user inputted strings to methods capable of evaluating 
code or running O.S. commands such as `eval`, `system`, `syscall`, `%x()`,
`open`, `popen<n>`, `File.read`, `File.write`, and `exec`. Using regular
expressions is a good way to sanitize it ([code sample](#command-injection-example)).
*Mitigates command injection attacks.*

Resources:
- [Ruby on Rails Security Guide - SQL Injection](http://guides.rubyonrails.org/security.html#sql-injection)
- [Rails SQL Injection Examples](https://rails-sqli.org/)
- [Step Up the Security of Your Rails App | Part 1](https://www.ombulabs.com/blog/rails/security/rails-security.html)

#### Authentication
Broken Authentication and Session Management are #2 at the [OWASP Top 10](https://www.owasp.org/index.php/Top_10_2013-Top_10).
- [ ] Avoid rolling your own authentication unless you know **exactly** what you
are doing. Consider using a gem such as
[Devise](https://github.com/plataformatec/devise),
[Authlogic](https://github.com/binarylogic/authlogic) or
[Clearance](https://github.com/thoughtbot/clearance). *Mitigates dozens of
potential vulnerabilities.*
- [ ] Enforce a minimum password length of 8 characters or more. *Mitigates
brute-force attacks.*
    - Devise: set `config.password_length = 8..128` in
    `config/initializers/devise.rb`. 
- [ ] Consider validating passwords against:
    - Dictionary words. Since passwords have a minimum length requirement, the
    dictionary need only include words meeting that requirement. 
    - A list of commonly used passwords such as
    [these](https://github.com/danielmiessler/SecLists/tree/master/Passwords).
    The [StrongPassword](https://github.com/bdmac/strong_password) gem provide
    such feature.
    - A leaked password database such as [PasswordPing](https://www.passwordping.com/docs-passwords-api/).
    - Context-specific words, such as the name of the application, the
    username, and derivatives thereof.
- [ ] Consider the pros and cons of enforcing password complexity rules such as
mixtures of different character types. Most applications use it. However, the
latest [NIST Guidelines](https://pages.nist.gov/800-63-3/sp800-63b.html) advise
against it. An alternative is to increase the minimum length requirement and
encourage the usage of passphrases. *Mitigate brute-force attacks.*
    - Devise: use a Devise-specific gem such as
    [devise-security](https://github.com/devise-security/devise-security),
    [devise_zxcvbn](https://github.com/bitzesty/devise_zxcvbn) or one of the 
    following authentication-agnostic solutions.
    - The [StrongPassword](https://github.com/bdmac/strong_password) gem or a
    regex validation ([code sample](#password-validation-regex)) should work
    with most authentication setups.
- [ ] Lock the account after multiple failed login attempts. *Mitigates 
brute-force attacks.*
    - Devise: activate the [lockable
    module](https://github.com/plataformatec/devise/wiki/How-To:-Add-:lockable-to-Users).
- [ ] Require users to confirm their e-mail addresses on sign-up and when the 
e-mail address is changed. *Mitigates the creation of bogus accounts with 
non-existing or third-party e-mails.*
    - Devise: use the [confirmable
    module](https://github.com/plataformatec/devise/wiki/How-To:-Add-:confirmable-to-Users)
    and set `config.reconfirmable = true` in `config/initializers/devise.rb`. 
- [ ] Require users to input their old password on password change. *Mitigates
unauthorized password changes on session hijacking, CSRF or when a user forgets 
to log out and leaves the PC or mobile device unattended.*
    - Devise: does that by default
- [ ] Expire the session at log out and expire old sessions at every successful
login. *Mitigates CSRF, session hijacking and session fixation attacks by 
reducing their time-frame.*
    - Devise: does that by default.
- [ ] Expire sessions after a period of inactivity (e.g., 30 minutes).
*Mitigates CSRF, session hijacking and session fixation attacks by reducing
their time-frame.* 
    - Devise: use the [timeoutable
    module](http://www.rubydoc.info/github/plataformatec/devise/Devise/Models/Timeoutable).
- [ ] Notify user via email on password change. *Does not prevent an attacker
from changing the victim's password, but warns the victim so he can contact the
system administrator to revoke the attacker's access.*
    - Devise: set `config.send_password_change_notification = true` in
    `config/initializers/devise.rb`.
- [ ] Use generic error messages such as "Invalid email or password" instead of
specifying which part (e-mail or password) is invalid. *Mitigates [user
enumeration](https://www.owasp.org/index.php/Testing_for_user_enumeration_(OWASP-AT-002))
and brute-force attacks.*
    - Devise: setting `config.paranoid = true` in
    `config/initializers/devise.rb` will protect the `confirmable`,
    `recoverable` and `unlockable` modules against user enumeration. To protect
    the `registerable` module, add a captcha to the registration page (see
    [instructions in the Devise
    Wiki](https://github.com/plataformatec/devise/wiki/How-To:-Use-Recaptcha-with-Devise)).
- [ ] Ensure all non-public controllers/actions require authentication. *Avoid
unauthorized access due to developer forgetfulness.*
    - Devise: add `before_action :authenticate_user!` to 
    `ApplicationController` and
`skip_before_action :authenticate_user!` to publicly accessible
controllers/actions. 
- [ ] Consider using two-factor authentication (2FA) as provided by
[Authy](https://www.authy.com/). *Provides a highly effective extra layer of
authentication security.*
    - Devise: see
    the [devise-two-factor](https://github.com/tinfoil/devise-two-factor) and
    [authy-devise](https://github.com/authy/authy-devise) gems. 
- [ ] Consider requiring authentication in `config/routes.rb`. Requiring
authentication in both controllers and routes may not be DRY, but such
redundancy provides additional security (see [Defense in
depth](https://en.wikipedia.org/wiki/Defense_in_depth_(computing))). 
    - Devise: Place non-public resources within a `authenticate :user do` block
    (see the [Devise
    Wiki](https://github.com/plataformatec/devise/wiki/How-To:-Define-resource-actions-that-require-authentication-using-routes.rb)).
- [ ] Consider limiting the number of simultaneous sessions per account. *May
 reduce application exposure on account compromise (e.g. leaked passwords).*
    - Devise: use the
    [devise-security](https://github.com/devise-security/devise-security)
    gem.
- [ ] Avoid implementing "security questions" such as "What is your mother's
maiden name?" as their answers may be reused across multiple sites and easily
found by means of [social
engineering](https://en.wikipedia.org/wiki/Social_engineering_(security)). See
[this article](https://www.wired.com/2016/09/time-kill-security-questions-answer-lies/).
- [ ] If using role-based access control (RBAC), do not include the role 
attribute in the strong parameters of the controller(s) used for user 
registration and profile editing. *Prevent malicious users from assigning admin 
role to themselves.* 
    - Devise: Do not pass the role parameter key to 
    `devise_parameter_sanitizer.permit`.
- [ ] Consider restricting administrator access by IP. If the client's IP is
dynamic, restrict by IP block/ASN or by country via IP geolocation.

#### Sessions & Cookies
Broken Authentication and Session Management are #2 at the [OWASP Top 10](https://www.owasp.org/index.php/Top_10_2013-Top_10).
- [ ] Don't store data such as money/point balances or user privileges in a
cookie or a CookieStore Session. Store it in the database instead. *Mitigates 
replay attacks.*
- [ ] Consider always using encrypted cookies. This is the default behavior in  
Rails 4+ when `secret_key_base` is set. *Strengthens cookie encryption and 
mitigates multiple attacks involving cookie tampering.*
- [ ] Unless your JavaScript frontend needs to read cookies generated by the
Rails server, set all cookies as `httponly`. Search the project for cookie
accessors and add `httponly: true`. Example: `cookies[:login] = {value: 'user',
httponly: true}`. *Restricts cookie access to the Rails server. Mitigates
attackers from using the victim's browser JavaScript to steal cookies after a
 successful XSS attack.*

Resources:
- [Ruby on Rails Security Guide - Sessions](http://guides.rubyonrails.org/security.html#sessions)

#### Cross-Site Scripting (XSS)
XSS is #3 at the [OWASP Top 10](https://www.owasp.org/index.php/Top_10_2013-Top_10).

###### Handling User Input
- [ ] Always validate user input that may eventually be displayed to other
users. Attempting to blacklist characters, strings or sanitize input tends to be
ineffective ([see examples of how to bypass such
blacklists](https://www.owasp.org/index.php/XSS_Filter_Evasion_Cheat_Sheet)). A
whitelisting approach is usually safer. *Mitigates multiple XSS attacks.*
- [ ] Consider using the
[loofah-activerecord](https://github.com/flavorjones/loofah-activerecord) gem
 to scrub your model attribute values. *Mitigates multiple XSS attacks*.
- [ ] If you must create links from user inputted URLs, be sure to validate
them. In particular, it should be possible to limit URL schemes to http/https
in nearly all cases. The URL passed to `link_to` (the second argument) will be
HTML escaped. However, `link_to` allows any scheme for the URL. If using regex,
ensure that the string **begins** with the expected protocol(s), as in
`\Ahttps?`. *Mitigates XSS attacks such as entering
`javascript:dangerous_stuff()//http://www.some-legit-url.com` as a website URL
or a dangerous `data:` payload that is displayed to other users (e.g., in a
user profile page).*
- [ ] When using regex for input validation, use `\A` and `\z` to match string 
beginning and end. Do **not** use `^` and `$` as anchors. *Mitigates XSS 
attacks that involve slipping JS code after line breaks, such as 
`me@example.com\n<script>dangerous_stuff();</script>`.* 
- [ ] Do not trust validations implemented at the client (frontend) as most 
implementations can be bypassed. Always (re)validate at the server.

###### Output Escaping & Sanitization
- [ ] Escape all HTML output. Rails does that by default, but calling
`html_safe` or `raw` at the view suppresses escaping. Look for calls to these
methods in the entire project, check if you are generating HTML from
user-inputted strings and if those strings are effectively validated. Note that
there are [dozens of ways to evade
validation](https://www.owasp.org/index.php/XSS_Filter_Evasion_Cheat_Sheet). If
possible, avoid calling `html_safe` and `raw` altogether. Most templating
libraries also provide a way of skipping escaping. ERB uses the double `==`:
`<%== params[:query] %>`. For custom scrubbing, see
[ActionView::Helpers::SanitizeHelper](http://api.rubyonrails.org/classes/ActionView/Helpers/SanitizeHelper.html)
*Mitigates XSS attacks.*
- [ ] Always enclose attribute values with double quotes. Even without
`html_safe`, it is possible to introduce cross-site scripting into templates
with unquoted attributes. In the following code
`<p class=<%= params[:style] %>...</p>`, an attacker can insert a space into
the style parameter and suddenly the payload is outside the attribute value and
they can insert their own payload. And when a victim mouses over the paragraph,
the XSS payload will fire. *Mitigates XSS attacks.*
- [ ] Rendering JSON inside of HTML templates is tricky. You can't just HTML
escape JSON, especially when inserting it into a script context, because
double-quotes will be escaped and break the code. But it isn't safe to not
escape it, because browsers will treat a `</script>` tag as HTML no matter
where it is. The Rails documentation recommends always using `json_escape`
just in case `to_json` is overridden or the value is not valid JSON.
*Mitigates XSS attacks.*
- [ ] Be careful when using `render inline: ...`. The value passed in will be
treated like an ERB template by default. Take a look at this code:
`render inline: "Thanks #{@user.name}!"`. Assuming users can set their own
name, an attacker might set their name to `<%= rm -rf / %>` which will execute
`rm -rf /` on the server! This is called Server Side Template Injection and it
allows arbitrary code execution (RCE) on the server. If you must use an inline
template treat all input the same as you would in a regular ERB template:
`render inline: "Thanks <%= @user.name %>"`. *Mitigates XSS attacks.*
- [ ] Avoid sending user inputted strings in e-mails to other users. Attackers
may enter a malicious URL in a free text field that is not intended to contain
URLs and does not provide URL validation. Most e-mail clients display URLs as
links. *Mitigates XSS, phishing, malware infection and other attacks.*
- [ ] If an I18n key ends up with `_html`, it will automatically be marked as html safe while the key interpolations will be escaped! See [(example code)](#when-i18n-key-ends-up-with-_html).

###### XSS protection in HAML templates

- [ ] Be careful when using `!=` in Haml and it should be made sure that no
user data is rendered unescaped. The `!=` notation in Haml works the way
`<%= raw(…) %>` works in ERB. See [(example code)](#haml-xss-protection).

Resources:
- [Ruby on Rails Security Guide - XSS](http://guides.rubyonrails.org/security.html#cross-site-scripting-xss)
- [OWASP XSS Filter Evasion Cheat Sheet](https://www.owasp.org/index.php/XSS_Filter_Evasion_Cheat_Sheet)
- [OWASP Ruby on Rails Cheatsheet - Cross-site Scripting (XSS)](https://www.owasp.org/index.php/Ruby_on_Rails_Cheatsheet#Cross-site_Scripting_.28XSS.29)
- [Plataformatec Blog - The new HTML sanitizer in Rails 4.2](http://blog.plataformatec.com.br/2014/07/the-new-html-sanitizer-in-rails-4-2)
- [Brakeman Pro - Cross-Site Scripting in Rails](https://brakemanpro.com/2017/09/08/cross-site-scripting-in-rails)
- [Preventing security issues in Rails](https://www.railscarma.com/blog/technical-articles/preventing-security-issues-rails/)
- [Security tips for rails apps](https://drivy.engineering/security-tips-for-rails-apps/)

###### Content Security Policy (CSP)
- [ ] Content Security Policy (CSP) is an added layer of security that helps to
detect and mitigate various types of attacks on our web applications, including
Cross Site Scripting (XSS) and data injection attacks.

Resources:
- [Rails 5.2 DSL for configuring Content Security Policy](https://blog.bigbinary.com/2018/10/23/rails-5-2-adds-dsl-for-configuring-content-security-policy-header.html)

#### Insecure Direct Object Reference
- [ ] An IDOR issue arises when the user is supposed to have access to url
`"/get/post/6"`, for example, but not `"/get/post/9"` but the system does not
properly check those permissions. And if we change "6" in the URL, what happens?
We can see the data of all users. This may be due to the fact that the data was
generated as follows: `@user = User.find_by(id: params[:user_id])` – which is
basically getting the ID from the GET parameter in the URL. Instead a more
secure way of doing this is setting the `@user` parameter based on the
`"current_user"` session variable like this: `@user = current_user`.

Resources:
- [Rails Vulnerabilities and Where To Find Them – Part 1](https://www.vdalabs.com/2018/01/12/rails-vulnerabilities-find-part-1/)

#### HTTP & TLS
- [ ] Force HTTPS over TLS (formerly known as SSL). Set 
`config.force_ssl = true` in `config/environments/production.rb`. May also be
 done in a TLS termination point such as a load balancer, Nginx or Passenger 
 Standalone. *Mitigates man-in-the-middle and other attacks.* 
- [ ] Use the [SSL Server Test tool from Qualys SSL
Lab](https://www.ssllabs.com/ssltest/) to check the grade of your TLS
certificate. Be sure to use the strongest (yet widely compatible) protocols
and cipher suites, preferably with Ephemeral Diffie-Hellman support. The  
[Mozilla SSL Configuration Generator](https://mozilla.github.io/server-side-tls/ssl-config-generator/) 
can give you some suggestions. *Mitigates multiple SSL/TLS-related attacks 
such as BEAST and POODLE.*
- [ ] Consider rate-limiting incoming HTTP requests, as implemented by the
[rack-attack](https://github.com/kickstarter/rack-attack) and
[rack-throttle](https://github.com/dryruby/rack-throttle) gems. See [sample
code](#throttling-requests). *Mitigates web scraping, HTTP floods, and other
attacks.*

###### Security-related headers
- [ ] Consider using the [Secure Headers
gem](https://github.com/twitter/secureheaders). *Mitigates several attacks.*
- [ ] Consider obfuscating the web server banner string. In other words, hide
 your web server name and version. *Mitigates HTTP fingerprinting, making it 
 harder for attackers to determine which exploits may work on your web server.*

#### Memcached Security

- [ ] Use a firewall. Memcached needs to be accessible from your other servers
but there's no reason to expose it to the internet. In short, only your other
production servers have access to your production memcached servers. This alone
would prevent your server from being used in an attack. Memcached out of the box
doesn't use authentication so anyone who can connect to your server will be able
to read your data.
- [ ] Listen on a private interface. If you're running one server for your Rails
application and memcached, you should listen on `127.0.0.1`. For availability
reasons, you shouldn't have 1 server in production anyway. For staging and test
environments, follow this rule. For production setups where you have multiple
Rails servers that need to connect to memcached, use the private IP of the
server. This is something like `192.168.0.1`, `172.16.0.1`, or `10.0.0.1`. When
you start memcached, use `--listen 127.0.0.1` or `--listen 192.168.0.1`.
- [ ] Disable UDP. It is enabled by default. To disable UDP, use `-U 0` when
starting memcached.

Resources:
- [Memcached Security aka Don't Attack GitHub](https://www.engineyard.com/blog/memcached-security-aka-dont-attack-github-)

#### Authorization (Pundit)
- [ ] Implement authorization at the back end. Hiding links/controls in the UI
is not enough to protect resources against unauthorized access. *Mitigates
forced browsing attacks.*
- [ ] Ensure all controllers/actions which require authorization call the 
`authorize` or `policy_scope` method ([sample code](#pundit-ensure-all-actions-are-authorized)).
*Mitigates forced browsing attacks due to developers forgetting to require 
authorization in some controller actions.*
- [ ] When using DB records associated to users to populate select
boxes, radio buttons or checkboxes, instead of querying by association
(`user.posts`), consider using `policy_scope`. See [additional details and sample
code](#pundit-ensure-all-actions-are-authorized). *Improves 
readability and maintainability of authorization policies.*

Resources:
- [Pundit: Ensuring policies and scopes are used](https://github.com/elabs/pundit#ensuring-policies-and-scopes-are-used)
- [Pundit: Scopes](https://github.com/elabs/pundit#scopes)

#### Files

###### File Uploads
- [ ] Avoid using user controlled filenames. If possible, assign "random" 
names to uploaded files when storing them in the OS. If not possible, 
whitelist acceptable characters. It is safer to deny uploads with invalid 
characters in the filenames than to attempt to sanitize them.
*Mitigates Directory Traversal Attacks such as attempting to overwrite 
system files by uploading files with names like `../../passwd`.*
- [ ] Avoid using libraries such as ImageMagick to process images and videos 
on your server. If possible, use an image/video processing service such as
[Transloadit](https://transloadit.com/),
[Cloudinary](http://cloudinary.com/features#manipulation), or
[imgix](https://www.imgix.com/solutions). *Mitigates multiple image/video 
processing related vulnerabilities such as [these](https://imagetragick.com).*
- [ ] If using [paperclip](https://github.com/thoughtbot/paperclip) gem with
[imagemagick](https://www.imagemagick.org) for file upload and processing, make
sure:
    - Imagemagick [policies](https://www.imagemagick.org/source/policy.xml) are
suited for your environment to avoid exploits like [pixel flood attack](
https://hackerone.com/reports/390).
    - Content spoofing is handled manually since it fails in scenarios like
[#2426](https://github.com/thoughtbot/paperclip/issues/2426).
- [ ] Process uploaded files asynchronously. If not possible, implement
per-client rate limiting. *Mitigates DoS Attacks that involve overloading the
server CPU by flooding it with uploads that require processing.*  
- [ ] Do not trust validations implemented at the client (frontend) as most 
implementations can be bypassed. Always (re)validate at the server.
- [ ] Validate files before processing. *Mitigates DoS Attacks such
 as image bombs.*
- [ ] Whitelist acceptable file extensions and acceptable Media Types (formerly 
known as MIME types). Validating file extensions without checking their media
 types is not enough as attackers may disguise malicious files by changing 
 their extensions. *Mitigates the upload of dangerous file formats such as shell
  or Ruby scripts.*
- [ ] Limit file size. *Mitigates against DoS attacks involving the 
upload of very large files.*
- [ ] Consider uploading directly from the client (browser) to S3 or a similar
cloud storage service. *Mitigates multiple security issues by keeping uploaded
files on a separate server than your Rails application.*
- [ ] If allowing uploads of malware-prone files (e.g., exe, msi, zip, rar,
pdf), scan them for viruses/malware. If possible, use a third party service to
scan them outside your server. *Mitigates server infection (mostly in Windows
servers) and serving infected files to other users.*
- [ ] If allowing upload of archives such as zip, rar, and gz, validate
the target path, estimated unzip size and media types of compressed files
**before** unzipping. *Mitigates DoS attacks such as zip bombs, zipping 
malicious files in an attempt to bypass validations, and overwriting of system 
files such as `/etc/passwd`.*

###### File Downloads
- [ ] Do not allow downloading of user-submitted filenames and paths. If not
possible, use a whitelist of permitted filenames and paths. *Mitigates the
exploitation of directory traversal vulnerabilities to download sensitive
files.*

Resources:
- [Ruby on Rails Security Guide - File Uploads and Downloads](http://guides.rubyonrails.org/security.html#file-uploads)

#### Cross-Site Request Forgery (CSRF)
- [ ] Enforce CSRF protection by setting `protect_from_forgery with: 
:exception` in all controllers used by web views or in 
`ApplicationController`.
- [ ] Use HTTP verbs in a RESTful way. Do not use GET requests to alter the
state of resources. *Mitigates CSRF attacks.*
- [ ] Up to Rails 4, there was a single CSRF token for all forms, actions, and
methods. Rails 5 implements per-form CSRF tokens, which are only valid for a
single form and action/method. Enable it by setting
`config.action_controller.per_form_csrf_tokens = true`.

Resources:
- [Ruby on Rails Security Guide - CSRF](http://guides.rubyonrails.org/security.html#cross-site-request-forgery-csrf)
- [Big Binary Blog - Each form gets its own CSRF token in Rails 5](http://blog.bigbinary.com/2016/01/11/per-form-csrf-token-in-rails-5.html)

#### Cross Origin Resource Sharing (CORS)
- [ ] Occasionally the need to share some resources across many domains appears.
For example, you want to upload a file using AJAX request and send it to the
other app. The receiving side should specify a whitelist of domains that are
allowed to make those requests. There are few HTTP headers that control that.

You can use `rack-cors` gem and in `config/application.rb` specify your
configuration ([code sample](#rack-cors-configuration)).

Resources:
- [Security issues solutions in RoR](https://syndicode.com/2017/10/23/security-issues-solutions-in-ror/)

#### Sensitive Data Exposure
- [ ] If possible, avoid storing sensitive data such as credit cards, tax IDs
and third-party authentication credentials in your application. If not 
possible, ensure that all sensitive data is encrypted at rest (in the DB) and
 in transit (use HTTPS over TLS). *Mitigate theft/leakage of sensitive data.*
- [ ] Do not log sensitive data such as passwords and credit card numbers. You
may include parameters that hold sensitive data in `config.filter_parameters` at
`initializers/filter_parameter_logging.rb`. For added security, consider
converting `filter_parameters` into a whitelist. See [sample
code](#convert-filter_parameters-into-a-whitelist). *Prevents plain-text storage
of sensitive data in log files.*
- [ ] HTML comments are viewable to clients and should not contain details that
can be useful to attackers. Consider using server-side comments such as `<%#
This comment syntax with ERB %>` instead of HTML comments. *Avoids exposure of
implementation details.*
- [ ] Avoid exposing numerical/sequential record IDs in URLs, form HTML source
and APIs. Consider using slugs (A.K.A. friendly IDs, vanity URLs) to identify
records instead of numerical IDs, as implemented by the [friendly_id
gem](https://github.com/norman/friendly_id). Additional benefits include SEO and
better-looking URLs. *Mitigates forced browsing attacks and exposure of metrics
about your business, such as the number of registered users, number of 
products on stock, or number of receipts/purchases.*
- [ ] If using slugs instead of numerical IDs for URLs, consider returning a
`404 Not Found` status code instead of `403 Forbidden` for authorization errors.
Prevents leakage of attribute values used to generate the slugs. For instance,
visiting `www.myapp.com/users/john-doe` and getting a `403`  return status
indicates the application has a user named John Doe.*
- [ ] Do not set `config.consider_all_requests_local = true` in the production
environment. If you need to set `config.consider_all_requests_local = true` to
use the [better_errors](https://github.com/charliesome/better_errors) gem, do it
on `config/environments/development.rb`. *Prevents leakage of exceptions and
other information that should only be accessible to developers.*
- [ ] Don't install development/test-related gems such as 
[better_errors](https://github.com/charliesome/better_errors) and 
[web-console](https://github.com/rails/web-console) in the production 
environment. Place them within a `group :development, :test do` block 
in the `Gemfile`. *Prevents leakage of exceptions and even **REPL access** 
if using better_errors + web-console.*

###### Credentials
- [ ] The encryption key, located on `config/master.key` is created when you run
`rails new`. It's also added to `.gitignore` so it doesn't get committed to your
repository. *Mitigates credential leaks/theft.*
- [ ] Don't edit the `config/credentials.yml.enc` file directly. To add
credentials, run `bin/rails credentials:edit`. Use a flat format which means you
don't have to put development or production anymore. *Mitigates credential
leaks/theft.*
- [ ] If you want to generate a new secret key base run, `bin/rails secret` and
add that to your credentials by running `bin/rails credentials:edit`.
- [ ] Upload `master.key` securely. You can scp or sftp the file. Upload the key
to a shared directory. Shared here means shared between releases, not a shared
filesystem. On each deploy, you symlink `config/master.key` to
`/path/to/shared/config/master.key`.
- [ ] If you need to give a developer a copy of the key, never send it via email
(unless you're using encrypted emails which most of us don't!) You can use a
password manager because they use encryption.
- [ ] Put the key on the `RAILS_MASTER_KEY` environment variable. In some cases
where you can't upload a file, this is the only option. Even though this is
convenient, make sure you know the risks of using environment variables. The
risks can be mitigated, but if you can upload master.key then use that option.

Resources:
 - [Rails Encrypted Credentials on Rails 5.2](https://www.engineyard.com/blog/rails-encrypted-credentials-on-rails-5.2)

#### Routing, Template Selection, and Redirection
- [ ] Don't perform URL redirection based on user inputted strings. In other 
words, don't pass user input to `redirect_to`. If you have no choice, create 
a whitelist of acceptable redirect URLs or limit to only redirecting to
paths within your domain [(example code)](https://www.owasp.org/index.php/Ruby_on_Rails_Cheatsheet#Redirects_and_Forwards).
*Mitigates redirection to phishing and malware sites. Prevent attackers from 
providing URLs such as 
`http://www.my-legit-rails-app.com/redirect?to=www.dangeroussite.com` to 
victims.*
- [ ] Do not use a user inputted string to determine the name of the template or
view to be rendered. *Prevents attackers from rendering arbitrary views such as
 admin-only pages.*
- [ ] Avoid "catch-all" routes such as `
match ':controller(/:action(/:id(.:format)))'` and make non-action controller 
methods private. *Mitigates unintended access to controller methods.*

Resources:
- [OWASP Ruby on Rails Cheatsheet - Redirects and Forwards (URL validation)](https://www.owasp.org/index.php/Ruby_on_Rails_Cheatsheet#Redirects_and_Forwards)

#### Third-party Software
- [ ] Apply the latest security patches in the OS frequently. Pay special 
attention to internet-facing services such as application servers (Passenger, 
Puma, Unicorn), web servers (Nginx, Apache, Passenger Standalone) and SSH 
servers. 
- [ ] Update Ruby frequently.
- [ ] Watch out for security vulnerabilities in your gems. Run 
[bundler-audit](https://github.com/rubysec/bundler-audit) frequently or use 
a service like [Snyk](https://snyk.io), [GuardRails](https://www.guardrails.io/) 
(both free for open-source development).

#### Security Tools
- [ ] Run [Brakeman](http://brakemanscanner.org/) before each deploy. 
If using an automated code review tool like 
[Code Climate](https://codeclimate.com/), enable the [Brakeman 
engine](https://docs.codeclimate.com/v1.0/docs/brakeman). 
- [ ] Adding a gem trust policy with `MediumSecurity` is a good way to stop
malicious gems getting installed on the server. For example,
`bundle --trust-policy MediumSecurity`.
- [ ] You can use `rubocop` gem and enables security-related rules in the
`.rubocop.yml` configuration file.
- [ ] Consider using a continuous security service such as
 [Detectify](https://detectify.com/).
- [ ] Consider using a Web Application Firewall (WAF) such as 
[NAXSI](https://github.com/nbs-system/naxsi) for Nginx, 
[ModSecurity](https://github.com/SpiderLabs/ModSecurity) for Apache and Nginx. 
*Mitigates XSS, SQL Injection, DoS, and many other attacks.*

Resources:
- [Keeping Rails Application Secured](https://fq.nz/blog/2019/04/14/keeping-rails-application-secured.html)
- [How RuboCop can secure your Ruby and Rails Applications](https://www.guardrails.io/blog/2018/11/25/how-rubocop-can-secure-your-ruby-and-rails-applications)

#### Testing
- [ ] Include security tests in your test suite. Look at OWASP's
[RailsGoat](https://github.com/OWASP/railsgoat) application for examples of
[security-related Capybara
specs](https://github.com/OWASP/railsgoat/tree/master/spec/vulnerabilities).
*Raises additional security awareness and mitigates security-related 
regressions.*
- [ ] Create security tests in pairs: one for the access denied scenario and 
another for the access granted scenario.
- [ ] When using TDD, consider implementing authentication in the early stages
 of development, as it tends to break multiple preexisting tests.

#### Others
- [ ] Use strong parameters in the controllers. This is the default behavior as
of Rails 4+. *Mitigates mass assignment attacks such as overwriting the `role`
attribute of the `User` model for privilege escalation purposes.*
- [ ] Implement Captcha or Negative Captcha on publicly exposed forms.
[reCAPTCHA](https://developers.google.com/recaptcha/) is a great option, and
there is [a gem](https://github.com/ambethia/recaptcha) that facilitates Rails
integration. Other options are the
[rucaptcha](https://github.com/huacnlee/rucaptcha) and
[negative-captcha](https://github.com/subwindow/negative-captcha) gems. 
*Mitigates automated SPAM (spambots).*

## Details and Code Samples

#### Command Injection example
```
# User input
params[:shop][:items_ids] # Maybe you expect this to be an array inside a string.
                          # But it can contain something very dangerous like:
                          # "Kernel.exec('Whatever OS command you want')"

# Vulnerable code
evil_string = params[:shop][:items_ids]
eval(evil_string)
```

If you see a call to eval you must be very sure that you are properly sanitizing
it. Using regular expressions is a good way to accomplish that.
```
# Secure code
evil_string = params[:shop][:items_ids]
secure_string = /\[\d*,?\d*,?\d*\]/.match(evil_string).to_s

eval(secure_string)
```

#### Password validation regex
We may implement password strength validation in Devise by adding the 
following code to the `User` model.
```
validate :password_strength

private

def password_strength
  minimum_length = 8
  # Regex matches at least one lower case letter, one uppercase, and one digit
  complexity_regex = /\A(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])/
  # When a user is updated but not its password, the password param is nil
  if password.present? &&
    (password.length < minimum_length || !password.match(complexity_regex))
    errors.add :password, 'must be 8 or more characters long, including 
                           at least one lowercase letter, one uppercase
                           letter, and one digit.'
  end
end
```

#### Pundit: ensure all actions are authorized

Add the following to `app/controllers/application_controller.rb`
```
after_action :verify_authorized, except: :index, unless: :devise_controller?
after_action :verify_policy_scoped, only: :index, unless: :devise_controller?
```

Add the following to controllers that do not require authorization. You may 
create a concern for DRY purposes.
```
after_action_skip :verify_authorized
after_action_skip :verify_policy_scoped
```

#### Pundit: only display appropriate records in select boxes
Think of a blog-like news site where users with `editor` role have access to
specific news categories, and `admin` users have access to all categories. The
`User` and the `Category` models have an HMT relationship. When creating a blog
post, there is a select box for choosing a category. We want editors only to see
their associated categories in the select box, but admins must see all
categories. We could populate that select box with `user.categories`. However,
we would have to associate all admin users with all categories (and update these
associations every time a new category is created). A better approach is to use
[Pundit Scopes](https://github.com/elabs/pundit#scopes) to determine which
categories are visible to each user role and use the `policy_scope` method when
populating the select box.

```
# app/views/posts/_form.html.erb
f.collection_select :category_id, policy_scope(Category), :id, :name
```

#### Convert filter_parameters into a whitelist
Developers may forget to add one or more parameters that contain sensitive data
to `filter_parameters`. Whitelists are usually safer than blacklists as they do
not generate security vulnerabilities in case of developer forgetfulness. 
The following code converts `filter_parameters` into a whitelist.

```
# config/initializers/filter_parameter_logging.rb
if Rails.env.production?
  # Parameters whose values are allowed to appear in the production logs:
  WHITELISTED_KEYS = %w(foo bar baz)
  
  # (^|_)ids? matches the following parameter names: id, *_id, *_ids
  WHITELISTED_KEYS_MATCHER = /((^|_)ids?|#{WHITELISTED_KEYS.join('|')})/.freeze
  SANITIZED_VALUE = '[FILTERED]'.freeze
  
  Rails.application.config.filter_parameters << lambda do |key, value|
    unless key.match(WHITELISTED_KEYS_MATCHER)
      value.replace(SANITIZED_VALUE)
    end
  end
else
  # Keep the default blacklist approach in the development environment
  Rails.application.config.filter_parameters += [:password]
end
```

#### rack-cors configuration

```
module Sample
  class Application < Rails::Application
    config.middleware.use Rack::Cors do
      allow do
        origins 'someserver.example.com'
        resource %r{/users/\d+.json},
          headers: ['Origin', 'Accept', 'Content-Type'],
          methods: [:post, :get]
      end
    end
  end
end
```

#### Throttling Requests

On some pages like the login page, you'll want to throttle your users to a few
requests per minute. This prevents bots from trying thousands of passwords
quickly.

Rack Attack is a Rack middleware that provides throttling among other features.

```
Rack::Attack.throttle('logins/email', :limit => 6, :period => 60.seconds) do |req|
  req.params['email'] if req.path == '/login' && req.post?
end
```

#### When I18n key ends up with \_html

Instead of the following example:
```
# en.yml
en:
  hello: "Welcome <strong>%{user_name}</strong>!"
```
```
<%= t('hello', user_name: current_user.first_name).html_safe %>
```
Use the next one:
```
# en.yml
en:
  hello_html: "Welcome <strong>%{user_name}</strong>!"
```
```
<%= t('hello_html', user_name: current_user.first_name) %>
```

#### HAML: XSS protection
By default,
```ruby
="<em>emphasized<em>"
!= "<em>emphasized<em>"
```
compiles to:
```ruby
&lt;em&gt;emphasized&lt;/em&gt;
<em>emphasized<em>
```

## Authors

- **Bruno Facca** - [LinkedIn](https://www.linkedin.com/in/brunofacca/) -
Email: bruno at facca  dot info

## Contributing

Contributions are welcome. If you would like to correct an error or add new 
items to the checklist, feel free to create an issue followed by a PR. See the
 [TODO](#TODO) section for contribution suggestions.

If you are interested in contributing regularly, drop me a line at the above
e-mail to become a collaborator.

## TODO
* Add sample tests (RSpec and/or Minitest) to detect the presence of
vulnerabilities. See OWASP's [RailsGoat security-related Capybara 
specs](https://github.com/OWASP/railsgoat/tree/master/spec/vulnerabilities) for
inspiration.
* Compare upload gems regarding their implementation of the [File
 Uploads](#file-uploads) items of this checklist (build a table).
* Compare authentication gems regarding their implementation of the
 [Authentication](#authentication) items of this checklist (build a table).

## References and Further Reading
- [Ruby on Rails Security Guide](http://guides.rubyonrails.org/security.html)
- [The Rails 4 Way by Obie Fernandez](https://www.amazon.com/Rails-Way-Addison-Wesley-Professional-Ruby/dp/0321944275/), Chapter 15
- [OWASP Top Ten](https://www.owasp.org/index.php/Top_10_2013-Top_10)
- [SitePoint: Common Rails Security Pitfalls and Their Solutions](https://www.sitepoint.com/common-rails-security-pitfalls-and-their-solutions/)
- [Rails Security Audit by Hardhat](https://github.com/hardhatdigital/rails-security-audit)
- [Rails Security Checklist by Eliot Sykes](https://github.com/eliotsykes/rails-security-checklist)
- [Ruby on Rails Security 17-Item Checklist](https://www.engineyard.com/blog/ruby-on-rails-security-checklist)
- [Rails security best practices](https://github.com/ankane/secure_rails)
- [Awesome Ruby Security resources](https://github.com/pxlpnk/awesome-ruby-security)
- [Awesome Rails Security](https://github.com/edwardqiu/awesome-rails-security)
- [Securing Sensitive Data in Rails](https://ankane.org/sensitive-data-rails)

## License

Released under the [MIT License](https://opensource.org/licenses/MIT).

zen-rails-security-checklist

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