Security firm Volexity just detailed a long-running intrusion by the China-linked group VerdantBamboo (UNC5221). The goal wasn’t a single server—it was corporate boundaries and infrastructure devices. After gaining access via Brickstorm, the attackers established proxy capabilities and used stolen credentials to reach Microsoft 365. Even worse: their traffic was designed to look like it originated from inside the company, helping it slip past Conditional Access rules that normally block external logins. How did investigators catch it? While hunting abnormal network activity, they found a Linux VM running Egnyte Storage Sync. The device wasn’t contacting Egnyte domains—instead, it pointed to attacker-controlled domains routed through Cloudflare. Snapshot analysis confirmed Brickstorm had been implanted. The team believes the credentials came from a compromised outsourced management provider. Using service-account access, attackers leveraged permission gaps to place the backdoor in high-privilege areas, starting it manually when needed. Brickstorm wasn’t alone: a second backup payload (AGENTPSD, Python) reportedly coexisted for ~18 months. Post-containment, the chain reignited: firewall admin exposure enabled an SSL VPN pivot and deployment of PLENET to a Synology NAS. #CyberSecurity #ThreatIntel #Microsoft365 #SupplyChainRisk #Egnyte #RansomwarePrevention
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