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Tuesday, April 28, 2020

Open URL Redirection Vulnerability- Well Explained


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 and can redirect you to another website(, so you’ll end up at even though the original request was made for 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, a TRUSTED website allows you to redirect to any other website. Then a malicious user can simply redirect to, 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.


      Let’s say there’s a “well known” website - And let’s assume that there’s a link like
      This link is to a sigup page, once you signup, you get redirected to which is specified in the HTTP GET Parameter redirectUrl.
      What happens if we change the to
      By visiting this url, if we get redirected to 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)

          $url_to_redirect = $_GET['redirect_url'];
          header('Location: ' . $url_to_redirect);
      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)

      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 = "";
      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=''" />
      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
      • 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
      • Try with double forward slashes
      • Try In this case the interpretation will be like, the is the username and will be the domain.
      • Test for javascript Protocol javascript:confirm(1).
      • Try 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 to bypass weak regex implementations.
      • Chinese seperator 。 as the dot - https://attacker%E3%80%82com.
      • Test for String reverser unicode(“\u202e”)
      • No slashes
      • Back slashes http:/\/\ or https:/\
      • Different domain resulting in redirection of which is not the same as
      • Try some unicode(including emojis) madness t𝐀 or 𝐀‘𝐀’ is “\uD835\uDC00”).



      Assume that the target is It has a password recovery page at 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
      If we tamper with the redirect parameter and change it to
      This redirects the user to an evil login page instead if the original one and the user can be phished.


      • 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.

      Friday, April 24, 2020

      Reflected XSS - Explained with a real world example


      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:

      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:<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.

      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.


      PUBG's main website 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.


      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
      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
      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.

      Thursday, April 23, 2020

      Cache Poisoned Denial of Service Simplified

      Suppose someone try to visit a website lets says "" 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 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: > Host:

      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

      User-Agent: Mozilla/5.0 … Firefox/57.0
      Accept: */*; q=0.01
      Accept-Language: en-US,en;q=0.5
      Accept-Encoding: gzip, deflate
      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

      User-Agent: Mozilla/5.0 … Firefox/57.0
      Cookie: language=pl;
      Connection: close

      GET /blog/post.php?mobile=1 HTTP/1.1

      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.

      Wednesday, April 22, 2020

      XSS found using host header injection

      This vulnerability arise when you give any input to the host parameter and it may reflect back .


      An attacker can use the vulnerability to construct a request that, if issued by another application user, will cause JavaScript code supplied by the attacker to execute within the user's browser in the context of that user's session with the application.

      Real World Example:

      Path : /billing-admin/profile/subscription/?l=de
      Payload : c5obc'+alert(1)+'p7yd5
      Steps to reproduce :
      Request Header :
      GET /billing-admin/profile/subscription/?l=de HTTP/1.1
      Accept: /
      Accept-Language: en
      User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0)
      Connection: close
      Overview :
      The payload c5obc'+alert(1)+'p7yd5 was submitted in the Referer HTTP header. Payload is copied from a request and echoed into the application's immediate response in an unsafe way.

      In the above example the payload reflect back in the response causing the rise of the vulnerability.

      Password Reset link hijacking via Host Header Poisoning

      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.


      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!



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

      HTTP Cache Poisoning via Host Header Injection


      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

      HTTP Response

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

      Now as you see we are able to see 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.

      Host Header attack

       In simple terms if a website is requested and when i change the host to , 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, Than click on go . If  not able to success . than try below method.
      2. Change host to and Set X-Forwarded-Host to original, if still unable to get success , try the below one
      3. Do the opposite to step two , Means change host to original and Set X-Forwarded-Host to original

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


      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:
      Payload: " X-Forwarded-Host: "
      How to reproduce this vulnerability:
      1. Open this URL " " 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


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

      Sunday, April 12, 2020

      SPF Record Missing is an important Security Concern

      What Is SPF/TXT Records?
      An SPF record is a type of Domain Name Service (DNS) record that identifies which mail servers are permitted to send email on behalf of your domain. The purpose of an SPF record is to prevent spammers from sending messages with forged From addresses at your domain.
      like : Suppose woodland company have email address as : , So if  I am able to send a mail using that address that means SPF records are not properly set .

      Checking Missing SPF:
      There Are Various Ways of Checking Missing SPF Records on a website But the Most Common and Popular way is
      Steps to Check SPF Records on a website:-
      Go to or mslookup
      Enter Target Website Ex: (Do Not Add https/http or www)
      Hit Check SPF (IF ANY)
      If You see any SPF Record than Domain is Not Vulnerable But if you see Nothing Here then "HURRAY! You Found a Bug"
      Once There is No SPF Records. An Attacker Can Spoof Email Via any Fake Mailer Like An Attacker Can Send Email From name "Support" and Email: "" .With Social Engineering Attack He Can TakeOver User Account Let Victim Knows the Phishing Attack but When He See The Email from the Authorized Domain. He Got tricked Easily.
      How to reproduce this
      1. fill all the details
        Name - mycrypto
        email -
        to - your email address
      Click on send email .It will directly send a mail from to you