Microsoft has uncovered stealthy and targeted malicious activity focused on post-compromise credential access and network system discovery aimed at critical infrastructure organizations in the United States.
The attack is carried out by Volt Typhoon, a state-sponsored actor based in China that typically focuses on espionage and information gathering.
Microsoft assesses with moderate confidence that this Volt Typhoon campaign is pursuing development of capabilities that could disrupt critical communications infrastructure between the United States and Asia region during future crises.
Volt Typhoon has been active since mid-2021 and has targeted critical infrastructure organizations in Guam and elsewhere in the United States. In this campaign, the affected organizations span the communications, manufacturing, utility, transportation, construction, maritime, government, information technology, and education sectors. Observed behavior suggests that the threat actor intends to perform espionage and maintain access without being detected for as long as possible.
To achieve their objective, the threat actor puts strong emphasis on stealth in this campaign, relying almost exclusively on living-off-the-land techniques and hands-on-keyboard activity. They issue commands via the command line to (1) collect data, including credentials from local and network systems, (2) put the data into an archive file to stage it for exfiltration, and then (3) use the stolen valid credentials to maintain persistence. In addition, Volt Typhoon tries to blend into normal network activity by routing traffic through compromised small office and home office (SOHO) network equipment, including routers, firewalls, and VPN hardware. They have also been observed using custom versions of open-source tools to establish a command and control (C2) channel over proxy to further stay under the radar.
In this blog post, we share information on Volt Typhoon, their campaign targeting critical infrastructure providers, and their tactics for achieving and maintaining unauthorized access to target networks. Because this activity relies on valid accounts and living-off-the-land binaries (LOLBins), detecting and mitigating this attack could be challenging. Compromised accounts must be closed or changed. At the end of this blog post, we share more mitigation steps and best practices, as well as provide details on how Microsoft 365 Defender detects malicious and suspicious activity to protect organizations from such stealthy attacks. The National Security Agency (NSA) has also published a Cybersecurity Advisory [PDF] which contains a hunting guide for the tactics, techniques, and procedures (TTPs) discussed in this blog.
As with any observed nation-state actor activity, Microsoft has directly notified targeted or compromised customers, providing them with important information needed to secure their environments. To learn about Microsoft’s approach to threat actor tracking, read Microsoft shifts to a new threat actor naming taxonomy.
Volt Typhoon achieves initial access to targeted organizations through internet-facing Fortinet FortiGuard devices. Microsoft continues to investigate Volt Typhoon’s methods for gaining access to these devices.
The threat actor attempts to leverage any privileges afforded by the Fortinet device, extracts credentials to an Active Directory account used by the device, and then attempts to authenticate to other devices on the network with those credentials.
Volt Typhoon proxies all its network traffic to its targets through compromised SOHO network edge devices (including routers). Microsoft has confirmed that many of the devices, which include those manufactured by ASUS, Cisco, D-Link, NETGEAR, and Zyxel, allow the owner to expose HTTP or SSH management interfaces to the internet. Owners of network edge devices should ensure that management interfaces are not exposed to the public internet in order to reduce their attack surface. By proxying through these devices, Volt Typhoon enhances the stealth of their operations and lowers overhead costs for acquiring infrastructure.
Post-compromise activity
Once Volt Typhoon gains access to a target environment, they begin conducting hands-on-keyboard activity via the command line. Some of these commands appear to be exploratory or experimental, as the operators adjust and repeat them multiple times.
Volt Typhoon rarely uses malware in their post-compromise activity. Instead, they rely on living-off-the-land commands to find information on the system, discover additional devices on the network, and exfiltrate data. We describe their activities in the following sections, including the most impactful actions that relate to credential access.
Discovery
Microsoft has observed Volt Typhoon discovering system information, including file system types; drive names, size, and free space; running processes; and open networks. They also attempt to discover other systems on the compromised network using PowerShell, Windows Management Instrumentation Command-line (WMIC), and the ping command. In a small number of cases, the threat actors run system checks to determine if they are operating within a virtualized environment.
Collection
In addition to operating system and domain credentials, Volt Typhoon dumps information from local web browser applications. Microsoft has also observed the threat actors staging collected data in password-protected archives.
