Connect with us

Hi, what are you looking for?



Researchers Leverage Voicemail Flaw to Compromise Messaging Apps

Italian security researchers have discovered a vulnerability that can be easily exploited to break into messaging applications such as Telegram, WhatsApp, and Signal.

Italian security researchers have discovered a vulnerability that can be easily exploited to break into messaging applications such as Telegram, WhatsApp, and Signal.

According to InTheCyber security researchers, the rather old voicemail caller-ID spoofing flaw can be leveraged to steal activation codes sent by messaging apps and compromise accounts. The researchers say that networks of two of the biggest mobile operators in Italy allow this kind of attack, explaining that the attacker only needs to know the victim’s phone number to be successful.

A security firm with offices in Milan and Lugano, InTheCyber explains that the bug can be exploited in at least three different scenarios where activation codes are sent to voicemail. All three, however, require for the user to not respond, to not be reachable, or to be engaged in different conversations.

The idea behind this attack is that, when an activation code is requested for a Telegram, WhatsApp, or Signal account, the code arrives via SMS. However, if the code isn’t introduced promptly, these services resend the activation via an automated call. Thus, if the user isn’t reachable, the call ends up in voicemail, and the attacker simply needs to look here for a vulnerability to exploit.

Calls are redirected to voicemail if the user doesn’t respond, is not reachable, or is occupied, and the security researchers explain that motivated attackers can leverage all three scenarios to execute an attack. An attacker could request the activation code late at night, could send multiple Silent-SMS to determine when the phone is detached from the network, or could set up a telephone scam to keep the phone busy during the attack.

Once the activation code has reached voicemail, the attacker can spoof his caller ID to impersonate the victim and gain access to both the target voicemail and to the activation code. The researchers have created a video to offer details on how the attack works and also publicly detailed the exploit on Monday, at the 7th National Conference on Cyber ​​Warfare in Milan.

The security researchers estimate there to be roughly 32 million users at risk on the networks of Wind and H3G. The obvious solution to this issue is to turn off voicemail, though both messaging services and wireless carriers should look into the matter and plug the security flaw.

Advertisement. Scroll to continue reading.

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

Click to comment

Daily Briefing Newsletter

Subscribe to the SecurityWeek Email Briefing to stay informed on the latest threats, trends, and technology, along with insightful columns from industry experts.

Join security experts as they discuss ZTNA’s untapped potential to both reduce cyber risk and empower the business.


Join Microsoft and Finite State for a webinar that will introduce a new strategy for securing the software supply chain.


Expert Insights

Related Content


Less than a week after announcing that it would suspended service indefinitely due to a conflict with an (at the time) unnamed security researcher...

Data Breaches

OpenAI has confirmed a ChatGPT data breach on the same day a security firm reported seeing the use of a component affected by an...

Risk Management

The supply chain threat is directly linked to attack surface management, but the supply chain must be known and understood before it can be...

IoT Security

A group of seven security researchers have discovered numerous vulnerabilities in vehicles from 16 car makers, including bugs that allowed them to control car...


Patch Tuesday: Microsoft warns vulnerability (CVE-2023-23397) could lead to exploitation before an email is viewed in the Preview Pane.


The latest Chrome update brings patches for eight vulnerabilities, including seven reported by external researchers.


A researcher at IOActive discovered that home security systems from SimpliSafe are plagued by a vulnerability that allows tech savvy burglars to remotely disable...


Patch Tuesday: Microsoft calls attention to a series of zero-day remote code execution attacks hitting its Office productivity suite.