Facebook Messenger Bug Lets Hackers Listen to You Before You Pick Up the Call

Facebook has patched a bug in its greatly set up Messenger application for Android that could have authorized a distant attacker to contact unsuspecting targets and hear to them before even they picked up the audio connect with.

The flaw was learned and claimed to Fb by Natalie Silvanovich of Google’s Venture Zero bug-hunting staff very last month on Oct 6 with a 90-day deadline, and impacts version 284…16.119 (and just before) of Facebook Messenger for Android.

In a nutshell, the vulnerability could have granted an attacker who is logged into the app to simultaneously initiate a simply call and mail a specially crafted information to a focus on who is signed in to both equally the app as properly as another Messenger shopper this kind of as the website browser.

“It would then trigger a scenario where, though the machine is ringing, the caller would begin acquiring audio either until the particular person staying referred to as answers or the contact moments out,” Facebook’s Stability Engineering Supervisor Dan Gurfinkel explained.

According to a specialized compose-up by Silvanovich, the flaw resides in WebRTC’s Session Description Protocol (SDP) — which defines a standardized format for the exchange of streaming media between two endpoints — allowing an attacker to send a exclusive type of message recognised as “SdpUpdate” that would cause the contact to connect to the callee’s gadget prior to being answered.

Audio and video clip calls via WebRTC normally does not transmit audio until eventually the receiver has clicked the settle for button, but if this “SdpUpdate” message is sent to the other stop machine though it is ringing, “it will induce it to start transmitting audio instantly, which could enable an attacker to check the callee’s surroundings.”


In some approaches, the vulnerability bears similarity to a privateness-eroding flaw that was documented in Apple’s FaceTime group chats element previous year that designed it probable for consumers to initiate a FaceTime online video call and eavesdrop on targets by including their personal quantity as a 3rd man or woman in a group chat even just before the man or woman on the other finish approved the incoming call.

The gaffe was deemed so significant that Apple pulled the plug on FaceTime group chats altogether in advance of it resolved the situation in a subsequent iOS update.

But unlike the FaceTime bug, exploiting the issue isn’t that effortless. The caller would have to currently have the permissions to simply call a specific particular person — in other words and phrases, the caller and the callee would have to be Fb good friends to pull this off.

What is more, the attack also necessitates that the lousy actor utilizes reverse engineering instruments like Frida to manipulate their possess Messenger application to force it to deliver the custom made “SdpUpdate” information.

Silvanovich was awarded a $60,000 bug bounty for reporting the concern, one particular amid Facebook’s 3 optimum bug bounties to date, which the Google researcher said she was donating to a non-revenue named GiveWell.

This not the initial time Silvanovich has found vital flaws in messaging applications, who has formerly unearthed a quantity of challenges in WhatApp, iMessage, WeChat, Sign, and Reliance JioChat, some of which have uncovered the “callee product to send out audio with no person conversation.”

Fibo Quantum