China-linked Storm-0940 used AI tool ARTEX to target 2,250 Microsoft 365 tenants, exploiting stolen ConnectWise credentials at machine speed.Microsoft published a detailed technical report naming Storm-0940, a China state-aligned group, as the actor behind the ConnectWise Cloud Backup supply chain compromise. The group used ARTEX, an open-source AI-driven penetration testing framework, to run attacks at machine speed against hundreds of organizations across aerospace, defense, energy, financial services, government, manufacturing, and more. “Several of these Storm-0940 ARTEX-driven attacks have resulted in the actor obtaining privileged access to an organization’s cloud infrastructure – including multiple instances where the time from initial targeting to privileged access was less than 3 hours.” reads the report. “Microsoft assesses that Storm-0940 was responsible for the recently disclosed ConnectWise supply chain compromise of a multi-tenant application.”Storm-0940 has been active since 2021 and has historically relied on password spraying and OAuth application abuse to get into Microsoft 365 environments. Adding ARTEX changed the scale of what they could do. In some attacks, the time between initial targeting and achieving privileged cloud access was under three hours.Before obtaining the ConnectWise credentials, Storm-0940 launched a password spraying attack between October 10 and 14. The attack came from the IP address 144.172.64[.]99. Microsoft recorded more than 151,000 failed login attempts against 327 accounts at eight organizations. Activity peaked on October 11, with 2,900 failed attempts per minute. Forty-eight accounts each received more than 1,000 failed attempts. None of these attempts succeeded.The situation changed on October 15, one day after the ConnectWise breach became public. The AI agents stopped trying passwords and switched to a different attack method. By then, Storm-0940 had obtained the credentials of several ConnectWise cloud application accounts. The agents used these credentials to log directly into customer Microsoft 365 environments.“Storm-0940’s use of ARTEX accelerated the speed of compromised application abuse to authenticate to Microsoft 365 customer environments through applications that had already been granted access.” Microsoft continues. “This allowed the threat actor to operate without requiring an interactive user sign-in. “The agents used applications that already had permission to access their targets. This allowed the attackers to enter customer environments without requiring users to sign in interactively.In a subset of environments where authentication succeeded, the agents didn’t stop there. They moved into Microsoft Graph and ran directory reconnaissance, modified application credentials to establish persistence, and attempted changes to identities, groups, and privileged roles. Microsoft identified multiple customer environments with evidence of this follow-on activity.The persistence mechanism is the part defenders need to act on now, even if they’ve already disabled the ConnectWise connections. “These changes can remain active as a backdoor even after the original compromised application is mediated.” says the IT giant.An attacker who added their own credentials to a trusted application before you revoked access still has a working key. Reviewing all service principal credential additions since at least October 1 is the right starting point, not October 15 when the public breach was announced.ARTEX is not a tool used only by Storm-0940. Microsoft says threat actors in several regions have used the same framework. Originally open-source, ARTEX was written in Go and can use different AI models to plan and carry out tasks. Researchers at Zscaler and Recorded Future also found a Chinese-speaking group using it to target South Korean financial institutions. The setup used DeepSeek, GLM, and Grok as coordinated AI agents, with GLM checking DeepSeek’s work. After these attacks became public, the project went closed-source. However, anyone who already has a copy can still use it.The speed point is what Microsoft keeps coming back to in its report. Agents don’t take weekends, don’t sleep, and can run multiple attack paths simultaneously. “This activity demonstrates how threat actors are integrating agentic AI into existing offensive security workflows and allows them to scale their operations exponentially.” Microsoft concludes. “Agents are not constrained by factors affecting humans – they can work around the clock, on weekends, and on holidays and attempt multiple breach paths simultaneously enabling significantly reduced time from selecting a target to achieving objectives, increasing the speed and impact of complex attacks like supply chain compromises.”When Storm-0940 had valid application credentials, they didn’t have to iterate slowly. They hit 2,250 tenants with 2,900 sign-in attempts per minute, a pace at which manual detection and response simply can’t keep up.Follow me on Twitter: @securityaffairs and Facebook and MastodonPierluigi Paganini(SecurityAffairs – hacking, ARTEX)