attackers 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.

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

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.

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

Based on Proofpoint analysis most login attempts originated 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.

Proofpoint researchers found 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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