ARMORY CASTLE Exploits BeyondTrust
Written by: Jayson Frost, Bryce Greathouse, Brian Meyer, John Palmisano, Rajesh Rajeshirke, Steve Rasch, John Wolfram
Introduction
On October 15, BeyondTrust disclosed a vulnerability, CVE-2026-102764, impacting BeyondTrust Remote Support (formerly Bomgar) appliances. BeyondTrust Remote Support is an enterprise secure remote access solution that enables IT teams to securely access and troubleshoot remote endpoints. The successful exploitation of this vulnerability results in the arbitrary upload of files.
During an incident response engagement, Mandiant identified evidence that ARMORY CASTLE, a suspected PRC-nexus espionage threat actor (formerly tracked as UNC5221), exploited this vulnerability as a zero-day, in late August 2026. This blog describes how ARMORY CASTLE escalated privileges and established persistent access to compromised BeyondTrust Remote Support appliances following exploitation of CVE-2026-102764, and provides actionable guidance for defenders.
Organizations should prepare for potential widespread exploitation following this disclosure, as ARMORY CASTLE and other threat actors have historically conducted broad, opportunistic exploitation once...
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