Cisco Duo's multifactor authentication service breached

A third-party provider that handles telephony for Cisco’s Duo multifactor authentication (MFA) service has been compromised by a social engineering cyberattack. Now Cisco Duo customers have been warned to be on alert for follow-on phishing schemes.

Customers were sent a notice explaining that the company handling SMS and VOIP multifactor authentication messaging traffic for Cisco Duo was breached on April 1. The threat actors reportedly used compromised employee credentials. Once inside the service provider’s systems, the unauthorized user downloaded SMS logs for specific users within a certain timeframe, the company said.

Cisco Duo did not identify the compromised telephony provider in its advisory.

“More specifically, the threat actor downloaded message logs for SMS messages that were sent to certain users under your Duo account between March 1, 2024 and March 31, 2024,” Cisco said in its customer advisory. “The message logs did not contain any message content but did contain the phone number, phone carrier, country, and state to which each message was sent, as well as other metadata (e.g., date and time of the message, type of message, etc.).”

Cisco advised impacted users to notify anyone whose information was exposed, and to remain vigilant against additional phishing attacks using the stolen data.

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