SecureAuth Named a Leader in KuppingerCole Leadership Compass Report for Customer Identity and Access Management
Widespread, Brute-Force, Cloud-to-Cloud Attacks Hit Office 365 Users

An operationalized cloud-to-cloud brute-force attack against Microsoft Office 365 users has hit high-level employees at multiple Fortune 2,000 organizations.

According to Skyhigh Networks, which remediated the attack, the perpetrators used popular cloud service platforms to conduct a persistent attack to log into corporate Office 365 accounts. The campaign had a “slow-and-low” pattern of coordinated attacks on high-value targets, including more than 100,000 failed Office 365 logins from 67 IP addresses and 12 networks. The attempts in all targeted 48 different organizations.

Skyhigh said that the duration and measured pace of the attacks suggest a determined effort and the desire to avoid detection. Within each organization, the attackers targeted a small number of senior employees across multiple departments.

The attackers tried logging in with different versions of employees’ Office 365 usernames, suggesting they may already possess some combination of employee names and passwords and were seeking valid Office 365 usernames for data access or spear phishing campaigns. Password data could have been obtained in a database breach of a service like Yahoo or a phishing attack, given that password reuse across accounts remains rampant.

Similarly, if the attackers confirmed an accurate Office 365 username with a correct reused password, they could successfully log into corporate Office 365 applications and potentially additional cloud service accounts.

“Sensitive data has already moved to cloud applications, so it is only natural sophisticated attacks are following,” said Slawomir Ligier, senior vice president of engineering at Skyhigh. “While companies traditionally have invested extensively in perimeter security, those without a dedicated cloud security solution will lack visibility and control for a growing category of attacks. Enterprise cloud providers secure their infrastructure, but the ultimate responsibility to control access to sensitive data lies with the customer.”

Cloud services are on path to become the standard for enterprise IT solutions, and Office 365, which offers cloud access to Microsoft Word, Excel and other productivity apps, has taken a dominant role with 58.4% of all sensitive corporate data in the cloud is stored in Office 365.

Keith Graham, CTO at SecureAuth, told Infosecurity that with 85 million users working on a combination of desktop and laptop computers, mobile devices and web applications, Office 365 is a primary target for attackers.

“Breaches tied to phishing e-mail scams and lack of strong identity security are accelerating, and the latest discovery of brute-force attacks against Office 365 serves as further proof of the need for organizations to prioritize their identity security,” he said.

“Typically, organizations using Office 365 have been forced to rely on traditional and inadequate username-password authentication to try to protect themselves from sophisticated attackers. Current versions of Office 365 mail clients support basic two-factor authentication while older Microsoft clients and third-party email applications do not. Because of this antiquated approach to authentication, attackers know that Office 365 is ripe to be exploited, and we anticipate attacks against Office 365 to proliferate for the foreseeable future.”

This article appeared on July 25 in Infosecurity Magazine.

For more information on SecureAuth’s enhanced Office 365 protection, visit

Pin It on Pinterest