Taking advantage of recent stolen credential dumps, attackers have been exploiting legacy protocols like IMAP to engage in high-volume password-spraying campaigns for the purpose of breaking into companies' cloud accounts, researchers at Proofpoint are reporting.

Used by email clients to retrieve messages from a server, IMAP (Internet Message Access Protocol) is an ideal protocol to abuse because it circumvents multi-factor authentication protections, Proofpoint explains in a March 14 blog post from its Information Protection Research team.

From September 2018 through February 2019, Proofpoint conducted a six-month study that analyzed over 100,000 unauthorized logins across millions of monitored cloud user-accounts. The company found that 60 percent of Microsoft Office 365 and G Suite tenants were targeted with IMAP-based password-spraying attacks, while 25 percent were successfully breached in this manner.

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