Massive IMAP-based password-spraying attacks successfully breached Microsoft Office 365 and G Suite accounts, circumventing multi-factor authentication (MFA) according to an analysis by Proofpoint.

As noted by Proofpoint's Information Protection Research Team in a recent report, during a "recent six-month study of major cloud service tenants, Proofpoint researchers observed attackers are targeting legacy protocols with stolen credential dumps to increase the speed and efficiency of the brute force attacks.

Based on Proofpoint study, IMAP is the most abused protocol, IMAP is the protocol that bypasses MFA and lock-out options for failed logins.

This technique takes advantage of the fact that the legacy authentication IMAP protocol bypasses MFA, allowing malicious actors to perform credential stuffing attacks against assets that would have been otherwise protected.

These intelligent new brute force attacks bring a new approach to the traditional normal brute force attack that uses the combination of usernames and passwords.

Based on the Proofpoint analysis of over one hundred thousand unauthorized logins across millions of monitored cloud user-accounts and found that:

▬ 72% of tenants were targeted at least once by threat actors
▬ 40% of tenants had at least one compromised account in their environment
▬ Over 2% of active user-accounts were targeted by malicious actors
▬ 15 out of every 10,000 active user-accounts were successfully breached by attackers

Their analysis unearthed the fact that around 60% of all Microsoft Office 365 and G Suite tenants have been targeted using IMAP-based password-spraying attacks and, as a direct result, approximately 25% of G Suite and Office 365 tenants that were attacked also experienced a successful breach.

On the whole, after crunching down the numbers, Proofpoint reached the conclusion that threat actors managed to reach a surprising 44% success rate when it came to breaching accounts at targeted organizations.

The ultimate aim of the attackers is to launch internal phishing and to have a strong foothold within the organization. Internal phishing attempts are hard to detect when compared to the external ones.