AJAX Security Cheat Sheet

Last revision (mm/dd/yy): 11/17/2016 Introduction This document will provide a starting point for AJAX security and will hopefully be updated and expanded reasonably often to provide more detailed information about specific frameworks and technologies. Client Side (Javascript) Use .innerText instead of .innerHtml The use of .innerText will prevent most XSS problems as it will automatically encode the text. Don't use eval Eval is evil, never use it. Needing to use eval usually indicates a problem in your design. Canonicalize data to consumer (read: encode before use) When using data to build HTML, script, CSS, XML, JSON, etc. make sure you take into account how that data must be presented in a literal sense to keep it's logical meaning. Data should be properly encoded before used in this manner to prevent injection style issues, and to make sure the logical meaning is preserved. Check out the OWASP Encoding Project. Don't rely on client logic for security Least ye have forgotten the user controls the client side logic. I can use a number of browser plugging to set breakpoints, skip code, change values, etc. Never rely on client logic. Don't rely on client business logic Just like the security one, make sure any interesting business rules/logic is duplicated on the server side less a user bypass needed logic and do something silly, or worse, costly. Avoid writing serialization code This is hard and even a small mistake can cause large security issues. There are already a lot of frameworks to provide this functionality. Take a look at the JSON page for links. Avoid building XML or JSON dynamically Just like building HTML or SQL you will cause XML injection bugs, so stay way from this or at least use an encoding library or safe JSON or XML library to make attributes and element data safe. XSS (Cross Site Scripting) Prevention SQL Injection Prevention Never transmit secrets to the client Anything the client knows the user will also know, so keep all that secret stuff on the server please. Don't perform encryption in client side code Use TLS/SSL and encrypt on the server! Don't perform security impacting logic on client side This is the overall one that gets me out of trouble in case I missed something :) Server Side Protect against JSON Hijacking for Older Browsers Use CSRF Protection Cross-Site Request Forgery (CSRF) Prevention Always return JSON with an Object on the outside Always have the outside primitive be an object for JSON strings: Exploitable: [{"object": "inside an array"}] Not exploitable: {"object": "not inside an array"} Also not exploitable: {"result": [{"object": "inside an array"}]} Avoid writing serialization code. Remember ref vs. value types! Look for an existing library that has been reviewed. Services can be called by users directly Even though you only expect your AJAX client side code to call those services the users can too. Make sure you validate inputs and treat them like they are under user control (because they are!). Avoid building XML or JSON by hand, use the framework Use the framework and be safe, do it by hand and have security issues. Use JSON And XML Schema for Webservices You need to use a 3rd party library to validate web services. Authors and Primary Editors Til Mas Michael Eddington Other Cheatsheets V - T - E Cheat Sheets Developer / Builder 3rd Party Javascript Management Access Control AJAX Security Cheat Sheet Authentication (ES) Bean Validation Cheat Sheet Choosing and Using Security Questions Clickjacking Defense Credential Stuffing Prevention Cheat Sheet Cross-Site Request Forgery (CSRF) Prevention Cryptographic Storage C-Based Toolchain Hardening CSS Security Deserialization DOM based XSS Prevention Forgot Password HTML5 Security HTTP Strict Transport Security Injection Prevention Cheat Sheet Injection Prevention Cheat Sheet in Java JSON Web Token (JWT) Cheat Sheet for Java Input Validation Insecure Direct Object Reference Prevention JAAS Key Management LDAP Injection Prevention Logging Mass Assignment Cheat Sheet .NET Security OS Command Injection Defense Cheat Sheet OWASP Top Ten Password Storage Pinning Query Parameterization REST Security Ruby on Rails Session Management SAML Security SQL Injection Prevention Transaction Authorization Transport Layer Protection TLS Cipher String Configuration Unvalidated Redirects and Forwards User Privacy Protection Web Service Security XSS (Cross Site Scripting) Prevention XML External Entity (XXE) Prevention Cheat Sheet Assessment / Breaker Attack Surface Analysis REST Assessment Web Application Security Testing XML Security Cheat Sheet XSS Filter Evasion Mobile Android Testing IOS Developer Mobile Jailbreaking OpSec / Defender Virtual Patching Vulnerability Disclosure Draft and Beta Application Security Architecture Business Logic Security Content Security Policy Denial of Service Cheat Sheet Grails Secure Code Review IOS Application Security Testing PHP Security Regular Expression Security Cheatsheet Secure Coding Secure SDLC Threat Modeling All Pages In This Category