Web Developer Security Checklist
Developing secure, robust web applications in the cloud is hard, very hard. If you think it is easy, you are either a higher form of life or you have a painful awakening ahead of you.
If you have drunk the MVP cool-aid and believe that you can create a product in one month that is both valuable and secure — think twice before you launch your “proto-product”.
After you review the checklist below, acknowledge that you are skipping many of these critical security issues. At the very minimum, be honest with your potential users and let them know that you don’t have a complete product yet and are offering a prototype without full security.
This checklist is simple, and by no means complete. I’ve been developing secure web applications for over 14 years and this list contains some of the more important issues that I’ve painfully learned over this period. I hope you will consider them seriously when creating a web application.
This is version 2 of the checklist. It has been re-organized from Version 1 and has a few new items by public demand (Thank you). While I try to keep the list tight and focused, please comment if you have an item that you think I should add to the list.
Credentials and Secrets
Store and distribute secrets using a key store designed for the purpose. Don’t hard code secrets in your applications and definitely don't store in GitHub!. For CMS fans, don't store your credentials in a file in the document directory.
Use a team-based password manager for all service passwords and credentials. NEVER email passwords or credentials to team members. Password Managers Reviewed.
Use multi-factor authentication for all your logins to service providers.
Ensure all passwords are hashed using appropriate crypto such as bcrypt. Never write your own crypto and correctly initialize crypto with good random data. Consider using an authentication service like Auth0 or AWS Cognito.
Use best-practices and proven components for login, forgot password and other password reset. Don’t invent your own — it is hard to get it right in all scenarios.
Implement simple but adequate password rules that encourage users to have long, random passwords.
Never, EVER have any undocumented and unpublicized means of access to the device including back-door accounts (like "field-service").
Run applications and containers with minimal privilege and never as root (Note: Docker runs apps as root by default).
Don't store sensitive data unless you truly need it. This means email addresses, personally identifying information and other personal information in general. Treat sensitive data like radioactive waste — i.e. there is an real, large and ongoing cost to securing it, and one day it can hurt you.
Keep a complete list of all the places you store sensitive information: databases, file systems, Dropbox, GitHub, Vault, Office docs and even the paper folder. This is useful to manage, required by GDPR and essential if hacked. You need to be able to locate all sensitive information.
If subject to GDPR, make sure you really understand the requirements and design it in from the start. For some, it will represent a major change in design and thinking. See Privacy Cheatsheet and Intro to GDPR.
Use encryption for data identifying users and sensitive data like access tokens, email addresses or billing details if possible (this will restrict queries to exact match lookups).
If your database supports low cost encryption at rest (like AWS Aurora), then enable that to secure data on disk. Make sure all backups are stored encrypted as well.
Use minimal privilege for the database access user account. Don’t use the database root account and check for unused accounts and accounts with bad passwords.
Fully prevent SQL injection by only using SQL prepared statements. For example: if using NPM, don’t use npm-mysql, use npm-mysql2 which supports prepared statements.
Secure development systems with equal vigilance to what you use for production systems. Build the software from secured, isolated development systems.
Ensure that all components of your software are scanned for vulnerabilities for every version pushed to production. This means O/S, libraries and packages. This should be automated into the CI-CD process.
Do client-side input validation for quick user feedback, but never trust it. Always validate and encode user input before displaying. Here is a useful checklist Client Side Checklist.
Validate every last bit of user input using white lists on the server. Consider generating validation code from API specifications using a tool like Swagger, it is more reliable than hand-generated code.
Never directly inject user content into responses. Never use untrusted user input in SQL statements or other server-side logic.
Use centralized logging for all apps, servers and services. You should never need SSH to access or retrieve logs. On AWS, consider CloudWatch with the SenseDeep Viewer.
Log with sufficient detail to diagnose all operational and security issues and NEVER log sensitive or personal information. Consider creating logs in JSON with high cardinality fields rather than flat text lines.
Don't emit revealing error details or stack traces to users and don't deploy your apps to production with DEBUG enabled.
Ensure that users are fully authenticated and authorized appropriately when using your APIs.
Use canary checks in APIs to detect illegal or abnormal requests that indicate attacks.
Segment your network and protect sensitive services. Use firewalls, virtual private networks and cloud Security Groups to restrict and control inbound and outbound traffic to/from appropriate destinations. AWS and CloudFlare both have excellent offerings.
Use TLS for the entire site, not just login forms and responses. Never use TLS for just the login form. Transitionally, use the strict-transport-security header to force HTTPS on all requests.
Cookies must be httpOnly and secure and be scoped by path and domain.
Use X-Frame-Option, X-XSS-Protection headers in client responses. Use https://observatory.mozilla.org to score your site.
Use HSTS responses to force TLS only access. Redirect all HTTP request to HTTPS on the server as backup.
Use CSRF tokens in all forms and use the new SameSite Cookie response header which fixes CSRF once and for all newer browsers.
Remove other identifying headers that can make a hackers job easier of identifying your stack and software versions.
Don't use GET requests with sensitive data or tokens in the URL as these will be logged on servers and proxies.
Ensure all services have minimum ports open. While security through obscurity is no protection, using non-standard ports will make it a little bit harder for attackers.
Host backend database and services on private VPCs that are not visible on any public network. Be very careful when configuring AWS security groups and peering VPCs which can inadvertently make services visible to the public.
Create test and staging resources in a separate AWS account to that used by production resources.
Isolate logical services in separate VPCs and peer VPCs to provide inter-service communication.
Ensure all services only accept data from a minimal set of IP addresses.
Restrict outgoing IP and port traffic to minimize APTs and “botification”.
Always use AWS IAM roles and not root credentials.
Use minimal access privilege for all ops and developer staff.
Regularly rotate passwords and access keys according to a schedule.
Ensure you can do upgrades without downtime. Ensure you can quickly update software in a fully automated manner.
Create all infrastructure using a tool such as Terraform, and not via the cloud console. Infrastructure should be defined as “code” and be able to be recreated at the push of a button. Have zero tolerance for any resource created in the cloud by hand — Terraform can then audit your configuration.
Don’t SSH into services except for one-off diagnosis. Using SSH regularly, typically means you have not automated an important task.
Don’t keep port 22 open on any AWS service groups on a permanent basis. If you must use SSH, only use public key authentication and not passwords.
Create immutable hosts instead of long-lived servers that you patch and upgrade. (See Immutable Infrastructure Can Be More Secure).
If not using Immutable Infrastructure (bad), ensure you have an automated system to patch and update all servers and regularly update your AMIs and rotate your servers to prevent long-lived APTs.
Power off unused services and servers. The most secure server is one that is powered down. Schedule dev servers to be powered down after hours when not required.
Denial of Service Protection
Make sure that DOS attacks on your APIs won’t cripple your site. At a minimum, have rate limiters on your slower API paths and authentication related APIs like login and token generation routines. Consider CAPTCHA on front-end APIs to protect back-end services against DOS.
Enforce sanity limits on the size and structure of user submitted data and requests.
Perform Chaos testing to determine how your service behaves under stress.
Consider using Distributed Denial of Service (DDOS) mitigation via a global caching proxy service like CloudFlare. This can be turned on if you suffer a DDOS attack and otherwise function as your DNS lookup.
Audit your design and implementation.
Do penetration testing — hack yourself, but also have someone other than you do pen testing as well.
Proactively test your app beyond normal use. Consider the OWASP test checklist to guide your test hacking.
Train staff (especially senior staff) as to the dangers and techniques used in security social engineering.
Have a threat model that describes what you are defending against. It should list and prioritize the possible threats and actors.
Setup a standard email account and web page dedicated for users to report security issues (firstname.lastname@example.org and /security).
Have a practiced security incident plan. One day, you will need it.
Security is a Journey
Most of all, remember that security is a journey and cannot be "baked-in" to the product just before shipping. I hope this checklist will prompt you through your entire development lifecycle to improve the security of your services.
Version 1 of this checklist can be found at Web Developer Security Checklist V1.
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