IMAP is the most exploited protocol. Office 365 and G Suite cloud accounts hacked

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One thing leads to another like a domino, with access to leaked credentials dumps, the speed and efficiency of brute-force attacks has improved significantly. Hackers have been targeting legacy protocols with these stolen credentials dumps. IMAP (Internet Message Access Protocol) is the most abused protocol, IMAP is the protocol that bypasses Multi-Factor Authentication and lock-out options for failed logins.

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.

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

Once in the attackers gain access, the attackers get closer to the ultimate aim which 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.

So the attackers try to gain login access to user’s cloud accounts and try to expand their infection through internal phishing.

Another interesting data point is the origin of these attacks based on the IP seems to be from:  Nigerian IP addresses(40%), next to that from China(26%) and other major sources are United States, Brazil, and South Africa.

The report shows that IMAP is the most abused protocol and the IMAP based attacks are higher in volumes between September 2018 and February 2019.

  • Approximately 60% of Microsoft Office 365 and G Suite tenants were targeted with IMAP-based password-spraying attacks
  • Roughly 25% of Office 365 and G Suite tenants experienced a successful breach as a result
  • Threat actors achieved a 44% success rate breaching an account at a targeted organization.

Researchers also established that “over 31% of all cloud tenants were subject to breaches originating from successful phishing campaigns.”

How the Phishing Attack Works?

Attackers compromise the user’s cloud accounts and then send internal phishing Email from the trusted accounts for lateral movements. Threat actors also use anonymization services such as VPNs or Tor nodes to hide their geo-location.


The attack has a higher percentage over educational institutions, especially university and high school students. The target includes other industries such as retail, finance, and technology.

The study indicates the increase that the threat actors increasing sophistication with brute force attacks to compromise cloud accounts at an unprecedented scale.



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