Pierluigi Paganini November 14, 2018

Security experts from Imperva reported a new Facebook flaw that could have exposed private info of users and their friends

A new security vulnerability has been reported in Facebook, the flaw could have been exploited by attackers to obtain certain personal information about users and their network of contacts.

The recently discovered issue raises once again the concerns about the privacy of the users of social network giant.

The vulnerability was discovered by security experts from Imperva, it resides in the way Facebook search feature displays results for queries provided by the users.

The good news for Facebook users is that this flaw has already been patched and did not allow attackers to conduct massive scraping of the social network for users’ information.

The page used to display the results of the users’ queries includes iFrame elements associated with each result, experts discovered that the URLs associated to those iFrames is vulnerable against cross-site request forgery (CSRF) attacks.

The website includes a javascript code that will get executed in the background when the victim clicks anywhere on that page.

“For this attack to work we need to trick a Facebook user to open our malicious site and click anywhere on the site, (this can be any site we can run JavaScript on) allowing us to open a popup or a new tab to the Facebook search page, forcing the user to execute any search query we want.” reads the analysis published by Imperva.

“Since the number of iframe elements on the page reflects the number of search results, we can simply count them by accessing the fb.frames.length property.

By manipulating Facebook’s graph search, it’s possible to craft search queries that reflect personal information about the user.”

Searching something like “pages I like named `Imperva`” the exports noticed they were forcing the social network to return one result if the user liked the Imperva page or zero results if not.

Composing specific queries it was possible to extract data about the user’s friends, below some interesting examples of queries provided by the experts:

• Check if the current Facebook users have friends from Israel: https://www.facebook.com/search/me/friends/108099562543414/home-residents/intersect
• Check if the user has friends named “Ron”: https://www.facebook.com/search/str/ron/users-named/me/friends/intersect
• Check if the user has taken photos in certain locations/countries: https://www.facebook.com/search/me/photos/108099562543414/photos-in/intersect
• Check if the current user has Islamic friends: https://www.facebook.com/search/me/friends/109523995740640/users-religious-view/intersect
• Check if the current user has Islamic friends who live in the UK: https://www.facebook.com/search/me/friends/109523995740640/users-religious-view/106078429431815/residents/present/intersect
• Check if the current user wrote a post that contains a specific text: https://www.facebook.com/search/posts/?filters_rp_author=%7B%22name%22%3A%22author_me%22%2C%22args%22%3A%22%22%7D&q=cute%20puppies
• Check if the current user’s friends wrote a post that contains a specific text: https://www.facebook.com/search/posts/?filters_rp_author=%7B%22name%22%3A%22author_friends%22%2C%22args%22%3A%22%22%7D&q=cute%20puppies

Below the video PoC published by Imperva:

The process can be repeated without the need for new popups or tabs to be open because the attacker can control the location property of the Facebook window using the following code.

Experts pointed out that mobile users are particularly exposed to such kind of attack because it is easy for them to forget open windows in the background allowing attackers to extract the results for multiple queries.

Imperva reported the flaw to Facebook through the company’s vulnerability disclosure program in May 2018, and the social network addressed the problem in a few days implementing CSRF protections.

Pierluigi Paganini

(Security Affairs – BCMPUPnP_Hunter botnet, hacking)

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