DRAFT CHEAT SHEET - WORK IN PROGRESS

Introduction

Cross site scripting is the most common web vulnerability. It represents a serious threat because cross site scripting allows evil attacker code to run in a victim’s browser. More details about XSS can be found here: https://www.owasp.org/index.php/Cross-site_Scripting_%28XSS%29

XSS Prevention Overview

Data Type	Context	Code Sample	Defense
String	HTML Body	<span>UNTRUSTED DATA</span>	HTML Entity Encoding
String	HTML Attribute, quoted	<span id="UNTRUSTED DATA"></span>	HTML Entity Encode single and double quotes
String	HTML Attribute, unquoted	<span id=UNTRUSTED DATA></span>	Aggressive HTML Entity Encoding
String	GET Parameter	<a href="/site/search?value=UNTRUSTED DATA">clickme</a>	URL Encoding
String	Untrusted URL rendered in an HREF tag (or other HTML link contexts)	<a href="UNTRUSTED DATA">clickme</a>	URL Validation reject javascript: URL’s Whitelist http, https and other safe URL types Attribute encoding safe URL verification
String	CSS	<div style="width: UNTRUSTED DATA;">Selection</div>	Strict structural validation CSS Hex encoding good design of CSS Features
String	JavaScript	<script>var currentValue='UNTRUSTED DATA';</script>	Ensure JavaScript variables are quoted JavaScript Hex Encoding JavaScript Unicode Encoding
String	JavaScript Event Handler Attribute	<input type="button" onclick="UNTRUSTED DATA" .../>	Ensure JavaScript variables are quoted JavaScript Hex or Unicode Encoding but NO backslash encoding (\" or \' or \\)
HTML Text	HTML Body	<span>UNTRUSTED HTML</span>	HTML Validation (JSoup, AntiSamy, HTML Sanitizer)
String	DOM XSS		DOM based XSS Prevention Cheat Sheet

Output Encoding Types

Encoding Type	Encoding Mechanism
HTML Entity Encoding	& --> & < --> < > --> > " --> " ' --> ' ' is not recommended / --> / forward slash is included as it helps end an HTML entity
HTML Attribute Encoding	TODO
URL Encoding	TODO
JavaScript HEX Encoding	TODO
CSS Hex Encoding	TODO

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
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Authors and Primary Editors

Jim Manico - jim [at] owasp.org
Jeff Williams - jeff [at] aspectsecurity.com

Abridged XSS Prevention Cheat Sheet

Contents

DRAFT CHEAT SHEET - WORK IN PROGRESS

Introduction

XSS Prevention Overview

Output Encoding Types

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