Why You Should Avoid Opening Voicemail Emails from Your Company’s Phone System

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Convenience has become the norm when it comes to workplace technology. One of the more recent developments has been the voicemail-to-email feature, which allows users to receive voicemails in text form directly in their inbox. While this has provided an efficient method of receiving messages, there is a dark side to this technology: it has become a prime target for phishing attacks, posing significant threats to organizations and their IT infrastructure.

One of the most notable incidents of this type occurred during an AT&T data breach. Unfortunately, these attacks are growing in both frequency and sophistication. At BrainStomp, we can provide guidance on how to better use this technology while still guarding your network against potential threats.

Convenience vs. Risk

Modern enterprise phone systems often include voicemail transcription services, which deliver a text or sound file version of messages via email. These usually arrive as an attachment or a .zip file. Opening such files, however, can create an opportunity for attackers to exploit vulnerabilities.

  • Email attachments are commonly used by cybercriminals to disguise malicious content.

  • Voicemail notifications closely resemble other internal emails, making it difficult to distinguish legitimate alerts from fake ones.

  • Spoofing tactics are constantly evolving, with attackers mimicking well-known phone service providers such as Microsoft Teams, Cisco, and RingCentral.

  • Many users fail to verify the legitimacy of voicemail alerts, often opening or downloading fake voicemails without realizing they are executing dangerous programs.

Exploiting Transcription Services

Cybersecurity researchers have identified various phishing methods that trick users into divulging their credentials or downloading malware. The emails typically include subject lines like this:

  • “You have a new voicemail from 212-555-0182”

  • “Missed Call: Listen to your voicemail”

  • “Voice Message Attached (1 New Message)”

When recipients click on the link, they are redirected to a spoofed Microsoft 365 login page or prompted to download malware, such as QBot, Agent Tesla, or DarkGate. Hackers typically target large organizations where voicemail traffic is extremely high and employees routinely open emails like this with regularity. That way, they are less likely to scrutinize every message.

The AT&T Data Breach

In 2024, AT&T confirmed a data breach affecting over 70 million customers. Compromised data included names, account numbers, and email addresses; in some cases, customers even had their passwords and Social Security numbers exposed.

Since the data breach, multiple threat intelligence firms have reported a notable increase in phishing emails targeting AT&T customers. With the stolen information, attackers are creating convincing communications that include personalized details.

Key impacts of this breach include:

  • More credible phishing emails leveraging stolen account information, including names, emails, and account numbers.

  • Spoofed voicemail emails mimicking services such as Microsoft Teams, Zoom Phone, and Avaya, enabling attackers to harvest system credentials and deliver malware.

  • A rise in malicious voicemails sent from seemingly legitimate corporate accounts.

How to Spot a Malicious Voicemail Email

At BrainStomp, we recognize voicemail phishing as a growing threat and provide resources to help organizations reduce risk.

Protecting against these attacks requires training employees and IT teams to identify suspicious messages. Warning signs include:

  • Typos in company names and email domains.

  • The .ZIP or .EXE files in attachments.

  • Urgent calls to action such as “listen to the message before it expires.”

  • Poor grammar or unusual formatting.

  • Requests for login credentials.

Best Practices for Organizations

There are several proactive steps organizations can take to guard against these types of attacks.  To mitigate risks, consider implementing the following measures:

  • Disable voicemail-to-email features entirely.

  • Implement advanced email filtering.

  • Enforce zero-trust device authentication and multi-factor authentication (MFA).

  • Provide ongoing employee security training and awareness programs.

  • Standardize legitimate voicemail emails so any email that isn’t formatted the same way is flagged as suspicious.

Caution Over Convenience

Convenience is a great draw for users in a large organization because it lowers the demands on IT staff and streamlines processes. However, it is becoming increasingly apparent that convenience often comes at a price. 

When a technology becomes a favorite target for attackers, organizations must reassess its value. In today’s threat landscape, where data breaches are increasingly common, caution should take priority over convenience.

Reach out today to BrainStomp for a consultation to evaluate the security of your voicemail-to-email system.