A large-scale password spraying campaign targeting Microsoft 365 environments through Microsoft’s Azure Command-Line Interface (Azure CLI) generated more than 81 million authentication attempts and compromised at least 78 user accounts across 64 organizations, according to cybersecurity firm Huntress.
Huntress said the activity was observed between June 12 and June 21, with attackers typically compromising two to four accounts per day before activity surged around June 22, when 23 organizations were affected. Most of the login attempts originated from AS32167, an autonomous system associated with hosting provider LSHIY LLC.
The company said the campaign formed part of a larger wave of credential-spraying attacks spanning multiple autonomous systems and noted that the volume of such attacks across its customer base has increased more than 155-fold during the past six months. Investigators believe the operation relied primarily on previously exposed username-and-password combinations obtained from credential leak collections.
A key element of the campaign was the use of the OAuth Resource Owner Password Credentials (ROPC) flow through Azure CLI. Although ROPC has been deprecated in OAuth 2.1, it can still exchange valid usernames and passwords directly for access tokens without an interactive sign-in prompt. Huntress said this allowed attackers to authenticate successfully in environments where multi-factor authentication policies did not fully cover that authentication flow.
The investigation identified several configuration gaps among affected organizations, including MFA policies applied only to certain cloud applications or user groups, enforcement limited to non-trusted locations, and policies that had been configured but never enforced. Huntress also found that eight impacted organizations had no MFA policy enabled.
Huntress emphasized that the findings should not be interpreted as evidence that MFA is ineffective. Instead, organizations should review Conditional Access policies, eliminate deprecated authentication methods where possible, ensure MFA protections apply to all supported sign-in flows, and monitor Azure CLI authentication activity for unusual login patterns.
The IPv6 address range used in the campaign belongs to LSHIY, an internet infrastructure provider registered in Hong Kong, Wuhan, China, and New York. Huntress said it reported the activity through the provider’s abuse-reporting channel but had not received a response.
