Hackers could have changed Facebook Messenger chat logs

Attackers could have rewritten logs of their Facebook Messenger chats with you to introduce falsehoods and malicious links

Here's a Facebook hack straight from the pages of the novel 1984: A way to rewrite the record of the past.

"Who controls the past controls the future: who controls the present controls the past," went the ruling party's slogan in George Orwell's dystopian novel.

Security researchers have found a way to control the past, by altering Facebook's logs of online chats conducted through its website and Messenger App.

Such modified logs could be used to control the future, the researchers suggest, by using them to commit fraud, to falsify evidence in legal investigations, or to introduce malware onto a PC or phone.

Roman Zaikin of Check Point Software Technologies discovered a flaw in Facebook's chat system that made it possible for an attacker to modify or remove any sent message, photo, file or link in a conversation they were part of.

He demonstrated in a video how he could change an earlier message from an innocent "Hi!" to what could be a link to ransomware attack.

But the chat logs could just as easily have been modified to create (or suppress) evidence of a spouse's unreasonable behavior in child custody battles, or any number of other scenarios.

Needing to be part of the conversation might seem a major limitation, but if attackers are somehow able to gain control of someone else's PC or Facebook account, then they are also able to modify all of that person's chat histories with other Facebook users.

"These chats can be admitted as evidence in legal investigations and this vulnerability opens the door for an attacker to hide evidence of a crime or even incriminate an innocent person," Check Point researchers wrote Tuesday, in a blog post describing the flaw.

The researchers found that each message in Facebook's chat applications is identified by a "message_id" parameter.

Given this identifier, it is possible to send instructions to Facebook's servers to modify the message. This can be done using common website debugging tools to alter the commands Facebook's own website used to send the chat messages in the first place, as Check Point's Zaikin demonstrated. The change in the log happens invisibly, without a fresh notification being sent to devices participating in the conversation.

Happily for future users of the Messenger app, Facebook has rewritten its past code to fix the flaw since being informed of it earlier this month, the vulnerability, the security company said in its blog post.

But if Check Point wasn't the first to spot the vulnerability, who knows what changes have already been made in the myriad documents composing our modern history? Has Oceania, as Orwell wrote, really always been at war with Eastasia?

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Peter Sayer

IDG News Service
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