The DFIR Report - thedfirreport.com/2025/09/29 September 29, 2025
Key Takeaways
The intrusion began with a Lunar Spider linked JavaScript file disguised as a tax form that downloaded and executed Brute Ratel via a MSI installer.
Multiple types of malware were deployed across the intrusion, including Latrodectus, Brute Ratel C4, Cobalt Strike, BackConnect, and a custom .NET backdoor.
Credentials were harvested from several sources like LSASS, backup software, and browsers, and also a Windows Answer file used for automated provisioning.
Twenty days into the intrusion data was exfiltrated using Rclone and FTP.
Threat actor activity persisted for nearly two months with intermittent command and control (C2) connections, discovery, lateral movement, and data exfiltration.
This case was featured in our September 2025 DFIR Labs Forensics Challenge and is available as a lab today here for one time access or included in our new subscription plan. It was originally published as a Threat Brief to customers in Feb 2025
Case Summary
The intrusion took place in May 2024, when a user executed a malicious JavaScript file. This JavaScript file has been previously reported as associated with the Lunar Spider initial access group by EclecticIQ. The heavily obfuscated file, masquerading as a legitimate tax form, contained only a small amount of executable code dispersed among extensive filler content used for evasion. The JavaScript payload triggered the download of a MSI package, which deployed a Brute Ratel DLL file using rundll32.
The Brute Ratel loader subsequently injected Latrodectus malware into the explorer.exe process, and established command and control communications with multiple CloudFlare-proxied domains. The Latrodectus payload was then observed retrieving a stealer module. Around one hour after initial access, the threat actor began reconnaissance activities using built-in Windows commands for host and domain enumeration, including ipconfig, systeminfo, nltest, and whoami commands.
Approximately six hours after initial access, the threat actor established a BackConnect session, and initiated VNC-based remote access capabilities. This allowed them to browse the file system and upload additional malware to the beachhead host.
On day three, the threat actor discovered and accessed an unattend.xml Windows Answer file containing plaintext domain administrator credentials left over from an automated deployment process. This provided the threat actor with immediate high-privilege access to the domain environment.
On day four, the threat actor expanded their activity by deploying Cobalt Strike beacons. They escalated privileges using Windows’ Secondary Logon service and the runas command to authenticate as the domain admin account found the prior day. The threat actor then conducted extensive Active Directory reconnaissance using AdFind. Around an hour after this discovery activity they began lateral movement. They used PsExec to remotely deploy Cobalt Strike DLL beacons to several remote hosts including a domain controller as well as file and backup servers.
They then paused for around five hours. On their return, they deployed a custom .NET backdoor that created a scheduled task for persistence and setup an additional command and control channel. They also dropped another Cobalt Strike beacon that had a new command and control server. They then used a custom tool that used the Zerologon (CVE-2020-1472) vulnerability to attempt additional lateral movement to a second domain controller. After that they then tried to execute Metasploit laterally to that domain contoller via a remote service. However they were unable to establish a command and control channel from this action.
On day five, the threat actor returned using RDP to access a new server that they then dropped the newest Cobalt Strike beacon on. This was then followed by an RDP logon to a file share server where they also deployed Cobalt Strike. Around 12 hours after that they returned to the beachhead host and replaced the BruteRatel file used for persistence with a new BruteRatel badger DLL. After this there was a large gap before their next actions.
Fifteen days later, the 20th since initial access, the threat actor became active again. They deployed a set of scripts to execute a renamed rclone binary to exfiltrate the data from the file share server. This exfiltration used FTP to send data over a roughly 10 hour period to the threat actor’s remote host. After this concluded there was another pause in threat actor actions.
On the 26th day of the intrusion the threat actor returned to the backup server and used a PowerShell script to dump credentials from the backup server software. Two days later on the backup server they appeared again and dropped a network scanning tool, rustscan, which they used to scan subnets across the environment. After this hands on activity ceased again.
The threat actor maintained intermittent command and control access for nearly two months following initial compromise, leveraging BackConnect VNC capabilities and multiple payloads, including Latrodectus, Brute Ratel, and Cobalt Strike, before being evicted from the environment. Despite the extended dwell time and comprehensive access to critical infrastructure, no ransomware deployment was observed during this intrusion.
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