Isn't it a MitM situation ? if you can intercept that value you can intercept more than a simple parameter no ? Le 11 juil. 2013 à 13:32, CANSIN YILDIRIM <canyildirim@xxxxxxxxx> a écrit : > ----------------------------------------------------- > #Title: Facebook Url Redirection Vulnerability > #Discovery Date: 10/July/2013 > #Author: Cansın Yıldırım > #Twitter: @YildirimCansin > #Website: www.cansinyildirim.com > ----------------------------------------------------- > > Introduction: > > The vulnerability reported on 10th July however Facebook Security Team > replied that it is an expected behaviour. That is why I don't see any > reason not to publish the vulnerability. More detailed background > information can be found on their website: > http://www.facebook.com/notes/facebook-security/link-shim-protecting-the-people-who-use-facebook-from-malicious-urls/10150492832835766 > > Decription: > > By obtaining user-specific hash value, an attacker redirect the user > to a malicious website without asking for verification. The hash value > can be found from the link that the user send to his/her wall. After > clicking on user's link,by setting BurpSuite Proxy, the attacker > intercept the parameters in the methods. > > Example url: http://www.facebook.com/l.php?u=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DSvWjWEyTLkg&h=3AQGbk0Cf&s=1 > > However we don't need s parameter, for the attacker most important > part of the url is the h paramater. > > Example h paramater = h=3AQGbk0Cf > > Now it is time to change the u paramater to a malicious site and send > it to user with the same h paramater > > Example malicious url: > http://www.facebook.com/l.php?u=cansinyildirim.com&h=3AQGbk0Cf > > Example malicious encoded url: > http://www.facebook.com/l.php?u=%63%61%6e%73%69%6e%79%69%6c%64%69%72%69%6d%2e%63%6f%6d&h=3AQGbk0Cf > > After the victim clicks on the link, Facebook redirects the victim to > a page specified by the attacker. > > Important note: I tried while the attacker and the victim were friends. > > > Proof of Concept: > > http://vimeo.com/70087250 > > http://www.cansinyildirim.com/facebook-url-redirection-vulnerability-2013/
