Open Redirect in bigbluebutton/greenlight
Jun 22nd 2022
The Greenlight end-user interface is vulnerable to Open Redirect vulnerability in Login page due to unchecked the value of
Proof of Concept
Original request example
POST /gl/u/login HTTP/1.1 Host: demo.bigbluebutton.org Cookie: return_to=https://demo.bigbluebutton.org/gl/; _ga=GA1.2.75174201.1655862571; _gid=GA1.2.1247108436.1655862571; _gat_gtag_UA_33131630_1=1; _greenlight-2_3_session=FLsZsD9232zlyzG5gVpasMmXpeQ9bi3ofhipRGi%2BaHwAQCmSenHDKMO9DRziK2dFlplKT56UZjt%2FnCQqrrDMnAk3Y77rXNUfQjMCOV3Zedc1SMic7yuqck%2FRj7u1nkVV4xusXpjBF7LtoBAVkPQ%3D--3sRNMFDT40mbgT5E--wxoTOWme4WbMq4xhoEdKzw%3D%3D Content-Length: 214 Cache-Control: max-age=0 Sec-Ch-Ua: "-Not.A/Brand";v="8", "Chromium";v="102" Sec-Ch-Ua-Mobile: ?0 Sec-Ch-Ua-Platform: "Windows" Upgrade-Insecure-Requests: 1 Origin: https://demo.bigbluebutton.org Content-Type: application/x-www-form-urlencoded User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/102.0.5005.63 Safari/537.36 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9 Sec-Fetch-Site: same-origin Sec-Fetch-Mode: navigate Sec-Fetch-User: ?1 Sec-Fetch-Dest: document Referer: https://demo.bigbluebutton.org/gl/signin Accept-Encoding: gzip, deflate Accept-Language: en-GB,en-US;q=0.9,en;q=0.8 Connection: close utf8=%E2%9C%93&authenticity_token=vp5XaMMhuNbjkU%2BV%2FsoSbroC7OLJxnPGaMCKgmgInH5TQbQ7R50EiKWd2mR7OxCcPQYbX66jZ4xVofJwOGdGtA%3D%3D&session%5Bemail%5D=<email>&session%5Bpassword%5D=<password>&commit=Sign+in
As you can see, there is a
return_to cookie in the request that will redirect user to a site in that value after user log in. If I change that cookie to another value, for example:
Now, forward the edited request and you will be redirected to
If you have an open redirection vulnerability, it makes many other attacks possible:
-Phishing: The most obvious way to use an open redirect is to steer the victim away from the original site to a site that looks the same, steal user credentials, and then return to the vulnerable website as if nothing happened.
-Server-Side Request Forgery (SSRF): Open redirects may be used to evade SSRF filters.
-Content-Security-Policy bypassing: If you use CSP to protect against XSS and one of the whitelisted domains has an open redirect, this vulnerability may be used to bypass CSP.
-CRLF Injection: If the redirection parameter allows line breaks, the attacker may try to perform response header splitting.