Overview
The STAC6451 threat actor cluster has recently been identified as a significant cyber threat targeting organizations in India. First observed in March 2024, the cluster has become notorious for exploiting vulnerable Microsoft SQL Server database instances that are directly exposed to the public internet. These SQL servers, often configured with default settings and weak credentials, become easy targets for brute-force attacks, providing the threat actors with an entry point to compromise networks. Once access is gained, the attackers use a combination of sophisticated tools and techniques to establish persistence, move laterally across the network, and deploy malicious payloads, including the Mimic ransomware.
Common targets
Information
India
Attack Vectors
Software Vulnerabilities
How they operate
The initial step in the STAC6451 attack chain involves brute-forcing exposed SQL servers to gain unauthorized access. Once inside, the attackers enable the xp_cmdshell stored procedure, a powerful SQL Server feature that is typically disabled by default but can be exploited to run operating system commands through the SQL Server service. This procedure enables the attackers to execute arbitrary commands on the server, essentially giving them control over the compromised system. By utilizing this capability, they can perform reconnaissance to gather valuable information, such as system version, hostname, and user credentials. This reconnaissance is highly automated, with attackers running specific commands in a uniform sequence across different victim environments, likely as part of a pre-programmed script.
Once the attackers have control over the compromised server, they proceed to stage their malicious payloads using the Bulk Copy Program (BCP). BCP is a command-line utility typically used to copy data between SQL instances and external files. However,
STAC6451 misuses this tool to export malicious files, including ransomware binaries, Cobalt Strike beacons, and privilege escalation tools, from the SQL database to a location on the compromised system. This method allows the threat actors to bypass traditional security measures by embedding their malicious tools within legitimate SQL database operations. By using BCP, they also ensure that the payloads are downloaded in a manner that does not immediately raise alarms, as the tool is native to SQL Server environments.
The next phase of the attack involves lateral movement and persistence. After deploying their tools, STAC6451 creates new user accounts with administrative privileges to maintain access to the compromised network. For instance, the group is known to create accounts like “ieadm,” “helpdesk,” and “admins124,” which are added to local administrator and remote desktop groups. These backdoor accounts ensure that the attackers can maintain access even if their initial entry point is discovered and mitigated. Additionally, the group uses tools like AnyDesk to establish remote access and control, further enabling their lateral movement across the network. One of the group’s key strategies for persistence is modifying the registry to enable the Wdigest authentication protocol, which forces the system to store credentials in plain text. This makes it easier for the attackers to retrieve and reuse credentials for further lateral movement within the environment.
STAC6451 also demonstrates adaptability in their attacks, as evidenced by the use of scripts that automatically adjust to different languages. During their campaigns, they have used commands in Portuguese, German, and French, suggesting that the group is not limited to specific geographic regions or languages. This flexibility enables them to scale their attacks and target organizations across various countries and industries. Furthermore, their use of automation throughout the attack lifecycle indicates a well-coordinated effort to quickly compromise multiple networks in parallel.
While Sophos MDR has successfully blocked ransomware deployment and other post-compromise activities in some cases, STAC6451 remains an active threat. Their continued exploitation of exposed SQL servers, combined with their use of sophisticated techniques like BCP staging and lateral movement through backdoor accounts, makes them a highly effective and persistent adversary. The group’s ability to adapt to different environments and their use of automated tools underscore the need for organizations to adopt robust security measures, including proper SQL server configuration, network segmentation, and continuous monitoring for suspicious activity.
