CORS bug on GOOGLE’s 404 page REWARDED!!!

This is a story of CORS bug that I found in one of Google’s aquisition -Kaggle,Where I got rewarded for CORS bug in 404 page.

One fine day I was looking at one of the aquisitions of Google-(Kaggle),Kaggle is used worldwide by Machine Learning community and is pretty famous.

I tried looking for CSRF bugs all over website but everything went in vain.I also searched for CORS misconfigurations but couldn’t find anything useful. I visited a 404 page accidentally and looked at it’s source code — It had a script tag whose body contained AntiForgery token which is the same token sent as X-XSRF-TOKEN in all the requests ,This is the CSRF token which is sent as headers in all the sensitive endpoints.

antiForgeryToken leaked via CORS misconfig in 404 page

I changed the origin header of 404 page to mydomain.tld then replayed the request and got the response — The header Access-Control-Allow-Origin and Access-Control-Allow-Credentials was set to mydomain.tld and True respectively.This means any other 3rd party domain is able to get and view response from only happens in the 404 page and is a CORS misconfig in 404 page only!!!

I quickly generated a POC ,which contained 2 parts :

  1. Get User specific Kaggle CSRF TOKEN from the 404 page.
  2. Using the CSRF Token from recieved from above to generate a API key on behalf of user.
Generate API KEY on begalf of user using CORS and CSRF bugs combined.

I then reported the GoogleVRP team about this incident with this POC and got rewareded with $$$ ,This time it was lower amount.A bug on Google’s aquisition is rewarded relatively lower compared to a bug on Google.

The GoogleVRP platform is always very friendly and is a great one for security researchers like me.I recommend everyone to try researching in this great Platform.

I would also like to mention and Thank about the GoogleVRP team’s great decision which benefits most of the Google security researchers community at this crucial COVID-19 time —

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