AI Agents Accelerate Microsoft 365 Attacks

Hackers aligned with China deployed artificial intelligence agents to attempt sign-ins at over 2,250 Microsoft 365 tenants in a large-scale attack targeting ConnectWise, Microsoft reported Thursday. The campaign, attributed to an actor designated Storm-0940, utilized stolen ConnectWise application credentials to authenticate directly as applications without requiring interactive user sign-in. Microsoft's Security blog detailed that some of these attacks reached privileged access in under three hours of initial targeting.

The operation involved ARTEX, an open-source framework that automates penetration testing using large language model-driven agents. Microsoft described ARTEX as a system that runs autonomous penetration tests capable of operating continuously with minimal human interaction. This automation significantly increased the speed of scanning, reconnaissance, and password spraying, leaving defenders with little time to detect and respond. It remains uncertain how the ConnectWise credentials were initially stolen or the total number of tenants actually compromised.

Storm-0940 has been active since 2021 and is classified as a China-state aligned actor with no known industry aliases. The group targeted 14 industries in total, including aerospace and defense, semiconductors, government, and think tanks. Microsoft emphasized that this activity did not result from a compromise of or a vulnerability within Microsoft's own systems, products, or services.

Automated password guessing targeted 327 accounts across eight organizations, generating more than 151,000 failed logons with no successful breaches. At its peak on October 11, the attack attempted 2,900 logons per minute, totaling over 111,000 attempts that day. Almost 98% of this activity was locked out. However, the attacking AI agents successfully signed in to customer tenants from a specific IP range using compromised application credentials, executing more than 200 sign-ins in under four minutes using four application credentials.

Security firm Huntress observed an application adding itself to a tenant's top administrator role on October 15, triggering a Microsoft Defender alert regarding self-assigned Global Administrator roles. Actions included planting new secrets set to expire in 2028. Huntress confirmed unauthorized sign-ins for 162 tenants by October 16 and nearly 1,000 Entra tenants a day later. ConnectWise has suspended several services as a precaution and started a phased restoration expected to take several days. Microsoft advises customers to keep affected app connections disabled until formal restoration instructions are issued.

The use of ARTEX, which can utilize any AI model, marks a departure from traditional attacks. Public reporting this month tied the technology to breaches at South Korean financial institutions. The developer of ARTEX, known as 'Autumn-27,' announced on GitHub that the project will no longer be updated and will become closed source.