New ‘Maggie’ Backdoor Targeting Microsoft SQL Servers

Security researchers with threat hunting firm DCSO CyTec are warning of a new backdoor that has been targeting Microsoft SQL (MSSQL) servers.

Dubbed Maggie, the threat is being deployed in the form of a signed Extended Stored Procedure (ESP) DLL file, a type of extension used by MSSQL. Once up and running on a target server, it can be controlled solely using SQL queries.

The backdoor supports numerous functions, including the ability to run commands and interact with files, and can be used by the attackers to gain a foothold into the compromised environment.

Additionally, Maggie can launch brute force attacks against other MSSQL servers, targeting admin accounts to add a hardcoded backdoor user.

To execute the backdoor on the target server, the attacker must place the ESP file in a directory that the MSSQL server can access, and needs valid credentials to load the ESP on the server.

DCSO CyTec notes that Maggie is manually loaded onto the server, after which it can start receiving SQL queries as commands.

Based on the received input, the backdoor can gather system information, can manipulate files and folders on the server, and can execute programs.

Furthermore, it can be used to enable network-related functionality, including TermService, a Socks5 proxy server, and port forwarding, which allow the backdoor to “act as a bridge head into the server’s network environment”, DCSO CyTec says.

Maggie also supports simple TCP redirection, which allows it to redirect incoming connections to a previously defined IP and port.

“The implementation enables port reuse, making the redirection transparent to authorized users, while any other connecting IP is able to use the server without any interference or knowledge of Maggie,” the security researchers say.

The backdoor also supports four commands linked to exploit usage – but which depend on a DLL that the attackers likely manually upload when needed – and two commands for brute forcing other MSSQL servers – for which a host, user and password list file needs to be provided, along with an optional thread count.

If the backdoor manages to successfully brute force an account that has admin rights, it proceeds with the creation of a backdoor user account on the target server. DCSO CyTec has identified 285 servers with the backdoor user on them, spread over 42 countries, with a focus on the Asia-Pacific region (mainly South Korea, India, and Vietnam).

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