Full Address Bar Spoofing On Opera Mini Android

Patience is indeed* a virtue — bug bounty

Piyush Raj ~ Rex
3 min readDec 25, 2020

I found a race condition flaw which caused browser to preserve the address bar and to load the content from the spoofed page. Address bar spoofing allows for attacks where a malicious page can spoof the identify of another site.


During my testing, it was observed that the browser allowed JavaScript to update the address bar while the page was still loading. Upon requesting data from a non-existent port the address was preserved and hence a due to race condition over a resource requested from non-existent port combined with the delay induced by setInterval function managed to trigger address bar spoofing. It causes browser to preserve the address bar and to load the content from the spoofed page.


Opera Mini Android is installed on more than 500,000,000+ devices. The vulnerability gives attackers the ability to steal data using phishing or spread misinformation using legitimate domains.

Most Address Bar Spoofing vulnerabilities are not very practical but this vulnerability not only spoofs the address bar, but also makes the spoofed web-page completely responsive so the attack becomes practical.

Expected behavior

The browser should handle load events in expected order when JS redirects page before sub-resource load finishes.

[1] https://bugs.webkit.org/show_bug.cgi?id=194131
[2] https://bugs.webkit.org/show_bug.cgi?id=194208


1) Visit the following link for the vulnerable browser — https://0x48piraj.com/--REDACTED--/operafabs.html

2) You will notice that the URL is pointing to https://www.opera.com:8080/, however the content is hosted on 0x48piraj.com.

The Great Plot

So, it all started when I got a reply from Opera Software saying,

Opera Software asking POC

The Proof of Concept

Before redirecting the user to the website with the closed port, I decoded the base64 encoded version of my evil page, and then added it to the DOM. I managed to keep the spoofed address stable by using the setinterval() function.

<title>Not Opera</title>
function spoof()
var data = 'PGh0bWw+PGJvZHk+PGgxIGFsaWduPSJjZW50ZXIiPlRoaXMgaXMgZGVmaW5pdGVseSBub3QgT3BlcmEuPC9oMT48L2JvZHk+PC9odG1sPg=='; // base64 encoded html content

The payload is <html><body><h1 align=”center”>This is definitely not Opera.</h1></body></html>.

Validation or say, “Oh my god, I really found a valid bug, I can’t believe it!” moment

The bug was found valid, …ob..viously?!

The “arm-twisting”

Hello there? Anyone?

I ❤ Opera‘s Responsiveness

Translation: OMG! I am a genius!

Finally! The bug fix moment

Aftermaths & The End

The Hall of Fame

Opera Security Hall of Fame (HoF)

Ho Ho Ho ..Merry Christmas!



Piyush Raj ~ Rex

Google Code-In C. Winner. GsOCer ‘19. Independent Security Researcher. Have hacked Medium, Mozilla, Opera & many more. Personal Website: https://0x48piraj.com