Open URL Redirection Vulnerability- Well Explained

Open URL Redirection Vulnerability- Well Explained

  April 28, 2020    Davinder

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Overview:

What are Redirects?

Redirect means allowing a website to forward the request for the resources to another URL/endpoint. Let’s assume that you make a request to davindertutorials.com and davindertutorials.com can redirect you to another website(new-davindertutorials.com), so you’ll end up at new-davindertutorials.com even though the original request was made for davindertutorials.com. This is called “redirection”. There are different types of redirects in HTTP, check em out below.

 

Now Lets understand this vulnerability:

Open redirect is basically what the name says, Openly allow Redirects to any website. 

URL redirection vulnerabilities found when user redirect to some other url , mainly the attacker url in unsafe way.

An attacker can construct a URL within the application that causes a redirection to an external domain. This behavior is well known for doing phishing attacks against users of the application.

Redirection Status Code - 3xx

• 300 Multiple Choices
• 301 Moved Permanently
• 302 Found
• 303 See Other
• 304 Not Modified
• 305 Use Proxy
• 307 Temporary Redirect
• 308 Permanent Redirect

The redirection can happen on the server-side or the client side.

Server-Side: Request to redirect is sent to the server, then the server notifies the browser to redirect to the url specified via the response.

Client-Side: Browser is notified to redirect to the url specified directly without the intervention of the server.

Why is this an issue?

Think about it for a moment, what if davindertutorials.com, a TRUSTED website allows you to redirect to any other website. Then a malicious user can simply redirect davindertutorials.com to attacker.com, and people fall for it all the time believing that it’s trusted, but infact, it’s not. So allowing redirects to any website without a stop in the middle or without a proper notification for the user is Bad.

Explanation

Let’s say there’s a “well known” website - https://example.com/. And let’s assume that there’s a link like

https://example.com/signup?redirectUrl=https://example.com/login

This link is to a sigup page, once you signup, you get redirected to https://example.com/login which is specified in the HTTP GET Parameter redirectUrl.

What happens if we change the example.com/login to attacker.com?

https://example.com/signup?redirectUrl=https://attacker.com/

By visiting this url, if we get redirected to attacker.com after the signup, this means we have an open redirect vulnerablility. This is a classic open redirect vulnerability.

Why does this happen?

This happens due to insufficient redirection checks in the back-end, which means the server is not properly checking if the redirect URL is in their whitelist or not. Here are some examples of vulnerable code

PHP (Server-Side)

<?php 
    $url_to_redirect = $_GET['redirect_url'];
    header('Location: ' . $url_to_redirect);
    die();

Here, the php code blindly grabs the url from redirect_url parameter and redirects to that url using the Location HTTP header.

Java (Server-Side)

 response.sendRedirect(request.getParameter("u"));

Here, a jsp page takes the url from the parameter u and blindly redirects it to the specified url.

Javascript (Client-Side)

window.location.href = "https://attacker.com";

We can assign the URL string to the location.href of window’s object. This will cause a redirect. If there are no checks inplace, then it’s a bug.

HTML (Client-Side)

<meta http-equiv="refresh" content="0;URL='http://attacker.com/'" />

HTML Meta tags can refresh the site with the given url as it’s content and also you can specify the refresh delay time.

How to find them?

• Visit every endpoint of the target to find these “redirect” parameters.
• View your proxy history, you might find something. Make sure to use filters.
• Bruteforcing helps too.
• You might uncover many endpoints by reading javascript code.
• Google is your friend, example query: inurl:redirectUrl=http site:target.com
• Understand and analyze where the redirection is needed in the target application like redirecting to dashboard after login or something like that.

Some tricks to find this bugs

• Test for basic modification of the url like target.com/?redirect_url=https://attacker.com.
• Try with double forward slashes target.com//attacker.com.
• Try target.com/@attacker.com. In this case the interpretation will be like, the target.com is the username and attacker.com will be the domain.
• Test for javascript Protocol javascript:confirm(1).
• Try target.com/?image_url=attacker.com/.jpg if there’s an image resource being loaded.
• Try IP address instead of the domain name.
• You can go further in terms of representing the IP in decimal, hex or octal.
• You can also try target.com/?redirect_url=target.com.attacker.com to bypass weak regex implementations.
• Chinese seperator 。 as the dot - https://attacker%E3%80%82com.
• Test for String reverser unicode(“\u202e”) target.com@%E2%80%AE@attacker.com.
• No slashes https:attacker.com.
• Back slashes http:/\/\attacker.com or https:/\attacker.com.
• Different domain redirect_url=.jp resulting in redirection of target.com.jp which is not the same as target.com.
• Try some unicode(including emojis) madness t𝐀rget.com or 𝐀ttacker.com(‘𝐀’ is “\uD835\uDC00”).

Exploitation

Phishing

Assume that the target is example.com. It has a password recovery page at example.com/forgot-password. You enter the email and you click on Forgot Password button, and it’ll send you an email with a password reset link, and this link might look like

https://example.com/reset-password/some-random-token?redirect=https://example.com/login

If we tamper with the redirect parameter and change it to

https://example.com/reset-password/some-random-token?redirect=https://attacker.com/login

This redirects the user to an evil login page instead if the original one and the user can be phished.

Mitigation

• Only use redirects if you really want em.
• If you want to use them, make sure you properly check the whitelisted domains and allow the matched ones.

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Reflected XSS - Explained with a real world example

Reflected XSS - Explained with a real world example

  April 24, 2020    Davinder

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OVERVIEW OF THE VULNERABILITY:

Reflected cross-site scripting (or XSS) arises when an application receives data in an HTTP request and includes that data within the immediate response in an unsafe way.

Suppose a website has a search function which receives the user-supplied search term in a URL parameter:

https://davindertutorials.com/search?term=hello

The application echoes the supplied search term in the response to this URL:

<p>You searched for: hello</p>

Assuming the application doesn't perform any other processing of the data, an attacker can construct an attack like this:

https://davindertutorials.com/status?message=<script>/*+Bad+stuff+here...+*/</script>

This URL results in the following response:

<p>You searched for: <script>/* Bad stuff here... */</script></p>

If another user of the application requests the attacker's URL, then the script supplied by the attacker will execute in the victim user's browser, in the context of their session with the application.

AFFECT OF THE VULNERABILITY
 
If an attacker can control a script that is executed in the victim's browser, then they can typically fully compromise that user. Among other things, the attacker can:

• Perform any action within the application that the user can perform.
• View any information that the user is able to view.
• Modify any information that the user is able to modify.
• Initiate interactions with other application users, including malicious attacks, that will appear to originate from the initial victim user.

There are various means by which an attacker might induce a victim user to make a request that they control, to deliver a reflected XSS attack. These include placing links on a website controlled by the attacker, or on another website that allows content to be generated, or by sending a link in an email, tweet or other message.

Because of the external delivery mechanism for the attack means that the impact of reflected XSS is generally less severe than stored XSS, where a self-contained attack can be delivered within the vulnerable application itself.


REAL WORLD EXAMPLE OF THIS VULNNERABILITY:

PUBG's main website https://www.pubg.com has an endpoint that is vulnerable to an injection vulnerability - namely a reflected injection of JavaScript, also known as Reflected Cross Site Scripting (XSS).

Steps To Reproduce:

How this can be done by attacker

Prepare a JavaScript payload that it wants the victim to execute. In this case, for Proof of Concept purposes, our JavaScript code will prompt an alert showing the users' cookies.

alert(document.cookie);

Inject this Javascript code properly into the vulnerable parameter, creating thus a crafted future GET request that will inject the payload.

GET /?p=iqz78'%3e%3cimg%20src%3da%20onerror%3dalert(document.cookie)%3d1%3echplq HTTP/1.1
Host: www.pubg.com
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0)
Connection: close
Referer: https://www.pubg.com/es/feed/
Cookie: _icl_current_language=en; _icl_visitor_lang_js=en-us; wpml_browser_redirect_test=0; __cfduid=de74423d435717d651b1c9e2c63f4acc21575460678

As this injection happens in a GET parameter, the attacker simply needs to send the crafted Link that produces this GET request to the victim and have the victim click it.

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Cache Poisoned Denial of Service Simplified

Cache Poisoned Denial of Service Simplified

  April 23, 2020    Davinder

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Suppose someone try to visit a website lets says "davindertutorials.com" than the request go to the server . But what if the website server is placed in US and I am surfing that website from India . Few minutes earlier my friend who is living near to me accessing that same website . So lets says davindertutorials.com server is in US but is taking services from cloudfare. So cloudfare DNS is holding copy of the page requested by me which is accessed by my friend few minutes earlier is saved in the cache of cloudfare.


Whenever a cache receives a request for a resource, it needs to decide whether it has a copy of this exact resource already saved and can reply with that, or if it needs to forward the request to the application server.


Simplified example of this attack :

> GET /index.html HTTP/1.1 > GET /index.html HTTP/1.1
> Host: example.com > Host: evil.com

Identifying whether two requests are trying to load the same resource can be difficult so requiring that the requests match byte-for-byte is not actually possible so Caches tackle this problem using the concept of cache keys – a few specific components of a HTTP request that are taken to fully identify the resource being requested. In the request above, I've highlighted the values included in a typical cache key in orange.


GET /blog/post.php?mobile=1 HTTP/1.1
Host: example.com
User-Agent: Mozilla/5.0 … Firefox/57.0
Accept: */*; q=0.01
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: https://google.com/
Cookie: jessionid=xyz;
Connection: close


This means that caches think the following two requests are equivalent, and will happily respond to the second request with a response cached from the first:

GET /blog/post.php?mobile=1 HTTP/1.1
Host: example.com
User-Agent: Mozilla/5.0 … Firefox/57.0
Cookie: language=pl;
Connection: close

GET /blog/post.php?mobile=1 HTTP/1.1
Host: example.com
User-Agent: Mozilla/5.0 … Firefox/57.0
Cookie: language=en;
Connection: close

This means that caches think the following two requests are equivalent, and will happily respond to the second request with a response cached from the first:

So now if you see, attacker have replaced the language in the cache .. so they can also make many other changes as well

To verify that the cache has been poisoned, just load the homepage in a browser and observe the popup.

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Password Reset link hijacking via Host Header Poisoning

Password Reset link hijacking via Host Header Poisoning

  April 22, 2020    Davinder

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This vulnerability raised when a website uses the Host header when sending out password reset links. This allows an attacker to insert a malicious host header, leading to password reset link / token leakage.

Developers often resort to the exceedingly untrustworthy HTTP Host header (_SERVER["HTTP_HOST"] in PHP or in another languages

There are two main ways to exploit this trust in regular web applications. 

The first approach is web-cache poisoning; manipulating caching systems into storing a page generated with a malicious Host and serving it to others.
The second technique abuses alternative channels like password reset emails where the poisoned content is delivered directly to the target.

Impact

The victim will receive the malicious link in their email, and, when clicked, will leak the user's password reset link / token to the attacker, leading to full account takeover.

Example for more understanding

1.) Open up Firefox and Burp Suite.)
2.) Visit the forgot password page (/index.php/login/concrete/forgot_password)
3.) Enter the victim's email address and click Reset and Email Password
4.) Intercept the HTTP request in Burp Suite & change the Host Header to your malicious site / server.
5.) Forward the request and you'll be redirected to your server.
The victim will then receive a password reset e-mail with your poisoned link.


If the victim clicks the link, the reset token will be leaked and the attacker will be able to find the reset token in the server logs. The attacker can then browse to the reset page with the token and change the password of the victim account!

Remediation

Use $_SERVER['SERVER_NAME'] rather than $_SERVER['HTTP_HOST']

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HTTP Cache Poisoning via Host Header Injection

HTTP Cache Poisoning via Host Header Injection

  April 22, 2020    Davinder

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Vulnerability:

Rewriting of links and URLs in cached pages to arbitrary strings by unauthenticated HTTP clients.When the application reflects HTTP Header value back in it's response and it may be possible to poison the server cache. The X-Forwarded-Host is directly reflected as a hyperlink. Than Host Header Attack - Cache Poisoning vulnerability may be there like:

Affected software: ANY site that does not validate HTTP Host: headers.

It is common practice for web programmers and web frameworks to rely on the value of the HTTP Host header to write links. This is for convenience, so that the same software will run on localhost, various testing servers, subdomains, secondary domains, etc, without modification. For example:

<a href="<?=$_SERVER['HTTP_HOST']?>/login">Login</a>

This turns out to be a very, very bad idea in any language. The HTTP Host header is arbitrary text controlled by the client, but common practice treats it as though it were a safe environment variable.

HTTP Request

GET / HTTP/1.1
Host: davindertutorials.com
X-Forwarded-Host: test.com
...
....

HTTP Response

HTTP/1.1 200 OK
....
....
....
<li class="SL_hide" title="Get New Relic on your iPad, iPhone, or Android phone"><a href="http://test.com/mobility">New Relic for iOS & Android</a></li>
....

Now as you see we are able to see test.com in the response.

Mitigation: DO NOT use the value of the Host header for anything. If you must, apply very strict filters to only allow valid FQDNs, and then whitelist the FQDNs you allow. Treat it as you would any arbitrary data coming from the outside. If your webserver is configured to output the value of the Host header (as in the example, and as by default in many webservers), disable that configuration.

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Host Header attack

Host Header attack

  April 22, 2020    Davinder

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 In simple terms if a website x.com is requested and when i change the host to y.com , if I am able to open the host . Than it is a host header attack.

Vulnerability Description: 

Open Redirection is sometimes used as a part of phishing attacks that confuse visitors about which web site they are visiting.

How to find this Vulnerability 

1. Change host to x.com, Than click on go . If  not able to success . than try below method.
2. Change host to x.com and Set X-Forwarded-Host to original domain.com, if still unable to get success , try the below one
3. Do the opposite to step two , Means change host to original domain.com and Set X-Forwarded-Host to original x.com

If you are unable to find success with the above written steps , Than may be the website is secured for this vulnerability.

Remediation:

If possible, the application should avoid incorporating user-controllable data into redirection targets. In many cases, this behavior can be avoided in two ways:

Remove the redirection function from the application, and replace links to it with direct links to the relevant target URLs.

Maintain a server-side list of all URLs that are permitted for redirection. Instead of passing the target URL as a parameter to the redirector, pass an index into this list.


Example of a Bug Reported:

Vulnerable URL:
https://wakatime.com/settings/account?apikeyrefresh=true
Payload: " X-Forwarded-Host: bing.com "
How to reproduce this vulnerability:

1. Open this URL " https://wakatime.com/settings/account?apikeyrefresh=true " and send it to the repeater in burp suite.
2. add the payload to the header request and forward the request.
3. It will directly redirect to bing.com

Impact

Impact:
Whenever a user visits this URL, it will redirect them to site.com. It is used in phishing attacks.

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