​Facebook Messenger flaw revealed

A new Facebook Messenger vulnerability has been detected that makes it possible for an attacker to modify or remove any sent message including rich content such as photos, files, and links.

Check Point, who discovered the flaw fully disclosed the issue to the Facebook Security team earlier this month. Facebook immediately responded, and after a joint effort the vulnerability was patched.

The flaw was revealed today at the Infosecurity Conference in London.

Check Point Security Researcher Roman Zaikin discovered the vulnerability which allows hackers to control a Facebook chat and adjust the messages according to their needs. Messages can be deleted or edited in an attack.

Each message sent through the Facebook chat application, whether through a browser or app, has its own unique identifier – the “message_id”. An attacker can store this request, containing the identifier, via a proxy while launching the malicious attempt.

Once the attacker has the message_id, he can alter the content of the message and send it to the Facebook servers. As the user has already received a notification through their browser or app from that message_id there is no notification sent to the user’s computer or mobile device.

As the message looks like it’s coming from a trusted source, the attacker can use the message as vector for many different purposes.

For example, a malicious user can manipulate message history as part of a fraud campaign. A malicious actor can change the history of a conversation to claim he had reached a falsified agreement with the victim, or simply change its terms.

Hackers can tamper, alter or hide important information in Facebook chat communications which can have legal repercussions. Chats can be admitted as evidence in legal proceedings and this vulnerability opened the door for an attacker to hide evidence of a crime or incriminate an innocent person.

The vulnerability can be used as a malware distribution vehicle. An attacker can change a legitimate link or file into a malicious one, or persuade a user to open a file with a malware payload.

And, as the message persists in the user’s chat history, it can be updated over time by the attacker as command and control servers, and other infrastructure used by cyber-criminals, is shut down and then reopened at a new address.

Oded Vanunu, Head of Products Vulnerability Research at Check Point, says “By exploiting this vulnerability, cybercriminals could change a whole chat thread without the victim realizing. What’s worse, the hacker could implement automation techniques to continually outsmart security measures for long-term chat alterations”.

You can watch a video demonstration of the flaw at here: