Proofpoint researchers in a recent six-month study of major cloud service tenants observed massive attacks that leveraged IMAP legacy protocols as well as credential dumps that have as their goal increasing the speed as well as the effectiveness of brute-force account compromises.
These IMAP-based "password-spraying" attacks were seen by Proofpoint to be breaching Microsoft Office 365 and Google G Suite accounts that were protected with multi-factor authentication (MFA).
Through their analysis of over 100,000 unauthorized logins across millions of monitored cloud user-accounts, they 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
Forty percent of all the successful malicious efforts originated from Nigerian IP addresses. The researchers found that between November 2018 and January 2019, successful brute-force and phishing-related attacks involving Nigerian IP addresses increased by 65%.
Twenty-six percent of the successful breaches were from logins from Chinese IP addresses, where most IMAP-based attacks originated. IMAP is a legacy authentication protocol that bypasses MFA. These attacks will avoid account lock-out by taking advantage of how IMAP is designed and will look like isolated failed logins. This means that they can be easily overlooked by the security team.
IMAP's design also goes around obstacles in authentication provided by MFA, which makes defeating MFA (even when it is correctly implemented) almost certain in an IMAP-based attack.
Office and G Suite were hit particularly hard by this approach. These attacks were found to target high-value users such as executives and their administrative assistants. The report says 60% of Microsoft Office 365 and G Suite users were targeted with IMAP-based password-spraying attacks, and that roughly 25% of Office 365 and G Suite users experienced a successful breach as a result.
Overall, threat actors achieved a 44% success rate breaching an account at an organization that had been targeted.
Attackers can parlay the successful compromises they gain into internal phishing attacks, lateral movement in organizations, as well as additional compromises at trusted external organizations.
MFA as a method has also been recently looked at by G Suite and found wanting. There is now an option for G Suite admins to disable telephony options as authentication methods for G Suite accounts in their domain. This is to prevent users from using SMS and voice codes when authenticating. These variations rely on external carrier networks that can be intercepted and manipulated by potential attackers.
While MFA may be a useful addition to the security mix in certain situations, over-reliance on it as a mechanism will be disappointing. Besides the systemic bypasses inherent in the IMAP protocol that the attacks researched by Proofpoint show, using telephony for MFA token transmittal may not be secure. MFA is not a magic bullet for security problems.
— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.