Facebook vulnerability allows to view hidden Facebook Friend List

Pierluigi Paganini November 23, 2013

Researcher Irene Abezgauz  from the Quotium Seeker Research Center discovered a Facebook flaw that allows anyone to see a profile’s private friend list.

Facebook is the privileged target for hackers and cybercriminals, the popular social network is a mine of data that could be used to acquire information on a specific target or to conduct criminal activities involving a large audience (e.g. Serve a malware, conduct a phishing campaign, arrange cyber fraud).Through the analysis of mutual relationship between users an attacker could elaborate the proper strategy to hit a victim, or a group of individuals. There are numerous tools that could be exploited to automatize the reconnaissance process through , and numerous are the functionality that could be used for useful researched.Recently I’ve published a post to describe the work of experts Werrett and Lee that demonstrated how to conduct a powerful analysis using FBStalker, a tool created to find a comprehensive amount of data on any Facebook user.

FBStalker reverse-engineers the Facebook Graph to find information on every user, the tool does not require a direct friendship with targeted profiles, it just needs to access to parts of victim’s posts marked as public.Through the use of Graph Search data mining activities has become very easy, Graph Search mines Facebook’s vast user data returning personalized results from natural-language queries. Using it is possible to discover what individuals like, where people have visited and if they share those same preferences with their friends.”

The study of friend list is another powerful practice to profile a target, but it is known that through privacy setting Facebook users can make the friend list public or private, if friend list is made private it will be not visible on publicly viewable profile.

The security researcher Irene Abezgauz  from the Quotium Seeker Research Center has discovered a Facebook flaw that allows anyone to see a users’ friend list, even when it is made private.

Facebook friend list


The researcher demonstrated how to access to the friend list abusing the Facebook feature “People You May Know” implemented by the social networks to suggests new friends to its users.

The feature analyzes Facebook mutual connections, related level, and many other criteria to suggests friends.
The first step is the creation of a fake Facebook profile used to send a friend request to the target account.
Even if the targeted user never accepted the request, the attacker could see that person’s friend list via the “People You May Know” feature. Clicking on the ‘see all’ button the attacker can expand the list to view hundreds of suggestions of users who are friends with the victim.

“As part of the research for this vulnerability we wanted to verify the exact conditions under which this was possible. The friends chosen for the victim were users who also had their friends list set to private. In addition, no interactions took place between the users except for the sending of friend requests. This is data which is not publicly available to any user who is not a friend of the victim.” states the post.

FB replied that:

”If you don’t have friends on Facebook and send a friend request to someone who’s chosen to hide their complete friend list from their timeline, you may see some friend suggestions that are also friends of theirs. But you have no way of knowing if the suggestions you see represent someone’s complete friend list.”

This Facebook hasn’t recognized Irene Abezgauz’s discovery, but maybe it’s better to evaluate it again in fact most of the friend list members is available to the attacker and even if it represents a partial friend list is a violation of user-chosen privacy controls.

Pierluigi Paganini

(Security Affairs – Facebook, social network)

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