U.S. and Canadian cybersecurity agencies are warning that China-sponsored threat actors are using BRICKSTORM malware to compromise VMware vSphere environments.
“Once compromised, the cyber actors can use their access to the vCenter management console to steal cloned virtual machine (VM) snapshots for credential extraction and create hidden, rogue VMs,” CISA, the NSA and the Canadian Centre for Cyber Security warned in the advisory.
Attacks have so far primarily targeted the government and IT sectors, the agencies said.
One PRC BRICKSTORM Malware Attack Lasted More Than a Year
CISA – the U.S. Cybersecurity and Infrastructure Security Agency – said it analyzed eight BRICKSTORM samples obtained from victim organizations, including one where CISA conducted an incident response engagement. While the analyzed samples were for VMware vSphere environments, there are also Windows versions of the malware, the agency said.
In the incident response case, CISA said threat actors sponsored by the People’s Republic of China (PRC) gained “long-term persistent access” to the organization’s network in April 2024 and uploaded BRICKSTORM malware to a VMware vCenter server. The threat actors also accessed two domain controllers and an Active Directory Federation Services (ADFS) server, successfully compromising the ADFS server and exporting cryptographic keys.
The threat actors used BRICKSTORM malware for persistent access “through at least Sept. 3, 2025,” the agency said.
BRICKSTORM is an Executable and Linkable Format (ELF) Go-based backdoor. While samples may differ in function, “all enable cyber actors to maintain stealthy access and provide capabilities for initiation, persistence, and secure command and control (C2),” the agencies said.
BRICKSTORM can automatically reinstall or restart if disrupted. It uses DNS-over-HTTPS (DoH) and mimics web server functionality “to blend its communications with legitimate traffic.”
The malware gives threat actors interactive shell access on the system and allows them to “browse, upload, download, create, delete, and manipulate files.” Some of the malware samples act as a SOCKS proxy to facilitate lateral movement and compromise additional systems.
PRC Hackers Got Access via a Web Server
CISA said that in its incident response engagement, the PRC hackers accessed a web server inside the organization’s demilitarized zone (DMZ) on April 11, 2024. The threat actors accessed it through a web shell present on the server.
“Incident data does not indicate how they obtained initial access to the web server or when the web shell was implanted,” CISA said.
On the same day, the hackers used service account credentials to move laterally using Remote Desktop Protocol (RDP) to a domain controller in the DMZ, where they copied the Active Directory (AD) database (ntds.dit).
The following day, the hackers moved laterally from the web server to a domain controller within the internal network using RDP and credentials from a second service account. “It is unknown how they obtained the credentials,” CISA said. The hackers copied the AD database and obtained credentials for a managed service provider (MSP) account. Using the MSP credentials, the hackers moved from the internal domain controller to the VMware vCenter server.
From the web server, the PRC hackers also moved laterally using Server Message Block (SMB) to two jump servers and an ADFS server, from which they stole cryptographic keys.
After gaining access to vCenter, the hackers elevated privileges using the sudo command, dropped BRICKSTORM malware into the server’s /etc/sysconfig/ directory, and modified the system’s init file in /etc/sysconfig/ to run the malware.
The modified init file controls the bootup process on VMware vSphere systems and executes BRICKSTORM, CISA said. The file is typically used to define visual variables for the bootup process. The hackers added an additional line to the script to execute BRICKSTORM from the hard-coded file path /etc/sysconfig/.
CISA, NSA, and the Canadian Cyber Centre urged organizations to use the indicators of compromise (IOCs) and detection signatures in their lengthy report to detect BRICKSTORM malware samples.
CISA also recommended that organizations block unauthorized DNS-over-HTTPS (DoH) providers and external DoH network traffic; inventory all network edge devices and monitor for suspicious network connectivity, and use network segmentation to restrict network traffic from the DMZ to the internal network.