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.
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.
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 the vulnerability becomes public.
Exploitation Mandiant identified evidence of CVE-2026-102764 exploitation within the access, syslog, messages, thin-scc, brain and SSL log files, which are only accessible via an LUKS-encrypted partition which contains the /home directory. We strongly recommend that affected organizations immediately apply the security patches provided by BeyondTrust to remediate the vulnerability, and review additional guidance in their blog.
Post-Exploitation Following the successful exploitation of CVE-2026-102764, Mandiant observed ARMORY CASTLE leverage multiple distinct TTPs to establish a foothold, escalate privileges, and enable lateral movement. Throughout the intrusion, ARMORY CASTLE leveraged a deep understanding of BeyondTrust appliance internals, as evidenced by their abuse of proprietary CLI utilities, startup configuration templates and local reverse-proxy routing. The threat actor used newly identified custom malware, the SAWFLY webshell and the BARECLAW tunneler to interact with the BeyondTrust device. Additionally, the actor routinely deleted appliance logs and endpoint artifacts to maintain access and evade detection.
In context
- Topic: Ciberseguridad — Riesgo, identidad, respuesta a incidentes y cumplimiento.
- Source: Google Cloud Blog
- Published: 15/10/2026
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Why it matters
Most incidents that end up being expensive did not start with a sophisticated technique. They started with an account that should have been closed when somebody resigned, a server nobody knew was still on, or a broad permission granted to unblock someone that then stayed forever.
I separate technical risk from business risk, because they do not always match. A critical vulnerability in an isolated system matters less than a medium one in the system that issues invoices. Prioritising by severity without looking at where the money is is an expensive way to work hard and protect little.
What usually goes wrong
The most expensive blind spot is usually the supplier. The organisation hardens its own perimeter and grants broad access to a third party that has half those controls. A good share of the incidents I have seen in this region came in that way, and the contract said nothing about it.
What to watch
- How it was communicated to customers and regulators, which is where reputational cost is decided.
- Whether third parties or suppliers were in the chain, because the perimeter now includes partners.
- How long it took to detect, usually the most revealing metric in the whole case.
How I read this entry
What I would review this very week is access: accounts belonging to people who left, permissions that grew without anyone trimming them, and shared credentials everybody swears do not exist. It is the least glamorous work and the one that cuts off the most attacks.
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Living through this in your own team?
Open the chat and tell me how you're handling it. I'm interested in comparing notes.
