Prial Islam

XSS bypass using META tag in

XSS bypass using META tag in

Hi readers,
Today I will write about a XSS Vulnerability I reported to the bug bounty Program.

Reflected XSS

A reflected XSS (or also called a non-persistent XSS attack) is a specific type of XSS whose malicious script bounces off of another website to the victim’s browser. It is passed in the query, typically, in the URL. It makes exploitation as easy as tricking a user to click on a link.

Vulnerable Endpoint:

To test a normal Reflected XSS I Input "><xsstest> in the Lang parameter and in source it was reflected properly inside META tag like below :-

<meta name="language" content=""><xsstest>" />

Looks simple right ? Then wait a little :’) . Then I Inputted "><img src=x> and I got:

Forbidden Error WAF postnl
Forbidden Error WAF postnl

I tried with many HTML tags and I got 2 points here:

  • Any Valid HTML tag is not allowed.
  • I can create any attributes here.

So I googled for meta tag attributes and got:

meta tag attributes
meta tag attributes

The http-equiv attribute took my attention. Now I again google more about it and learned that "META tag has the http-equiv directive. This directive allows you to define the equivalent of an HTTP header in the HTML code. The http-equiv directive can take a value of refresh, which can be used to redirect a user to another page."

Then I input 0;"HTTP-EQUIV="refresh" and response was

<meta name="language" content="0;"HTTP-EQUIV="refresh"" />

And I got redirected to So I have open redirection now. Now we can try for Data URI XSS. So I input 0;javascript:alert(1)"HTTP-EQUIV="refresh" and response was

Forbidden Error WAF postnl
Forbidden Error WAF postnl

This was again Triaged for the keyword javascript used in payload. So I used Base64 encoded payload 0;data:text/html;base64,PHNjcmlwdD5wcm9tcHQoIlJlZmxlY3RlZCBYU1MgQnkgUHJpYWwiKTwvc2NyaXB0Pg=="HTTP-EQUIV="refresh" and response source was

<meta name="language" content="0;data:text/html;base64,PHNjcmlwdD5wcm9tcHQoIlJlZmxlY3RlZCBYU1MgQnkgUHJpYWwiKTwvc2NyaXB0Pg=="HTTP-EQUIV="refresh"" />

And now when I visit I got XSS popup

XSS Popup in different origin from postnl
XSS Popup in different origin from postnl

I reported it to their Zerocopter report form. Then they deployed a Fix by blacklisting the data:text/html;base64 keyword like they have blacklisted JavaScript keyword

After the fix still I can do Open Redirect when a user visits: and confirmed with them again

PostNL open redirect
PostNL open redirect

They again Fixed the issue and listed My name on their Hall Of Fame page & also offered to send some goodies 😍

Goodies offer from PostNL
Goodies offer from PostNL

Thanks for reading.If you have any query ask me on Facebook

Leave a Reply

Your email address will not be published. Required fields are marked *

Recent tweets

@naglinagli @0xCOD3 Congratulations @0xCOD3 , waiting for the workflow on this ❤️ Read More

Jan 27 2021, 8:20 am

@imranHudaA @naglinagli @PrettyRecon I can see 5 subdomain. One is base domain here. Read More

Jan 26 2021, 5:34 pm

@BrianBitange1 @naglinagli You got my github endpoints what I used to takeover 😷 Read More

Jan 26 2021, 1:43 pm

@Bugcrowd MVP swag arrived 🥰🔥 #BugBounty #ItTakesACrowd ❤️ Read More

Jan 06 2021, 1:45 pm

2021 started with @Hacker0x01 #Hacker0x01 #TogetherWeHitHarder ❤️ Read More

Jan 05 2021, 7:38 pm

RT @hunter0x7: Read More

Jan 05 2021, 12:13 pm

Recent posts