APT37: Rust Backdoor & Python Loader

2025-09-08 Zscaler

https://www.zscaler.com/blogs/security-research/apt37-targets-windows-rust-backdoor-and-python-loader

Thumbnail for APT37: Rust Backdoor & Python Loader

Zscaler ThreatLabz details recent APT37 activity against Windows systems, linking the North Korean-aligned actor to Rustonotto, Chinotto, and FadeStealer. The campaigns use Windows shortcut files and CHM help files as initial delivery vectors, including a shortcut that launches Chinotto, drops a decoy HWP document titled “Two Perspectives on North Korea in South Korean Society,” and installs the Rustonotto backdoor with a MicrosoftUpdate scheduled task. Rustonotto receives Base64-encoded Windows commands from a C2 server and returns Base64-encoded execution results, while CHM-delivered Chinotto provides file transfer, command execution, registry modification, archive extraction, and scheduled-task capabilities through HTTP POST communications. Follow-on hands-on-keyboard activity delivered CAB-packaged Python launchers and used Process Doppelgänging-style injection to deploy FadeStealer, a surveillance tool for keystrokes, screenshots, audio, device monitoring, removable media tracking, and RAR-based data exfiltration. The report matters because it shows APT37 adopting Rust and Python-based tradecraft while continuing targeted operations against South Korean individuals connected to North Korea issues and human rights activism.

Indicators of Compromise

Type Value First Seen Last Seen
HASH d2b34b8bfafd6b17b1cf931bb3fdd3db 2025-09-08 2025-09-26
HASH 89986806a298ffd6367cf43f36136311 2025-09-08 2025-09-26
HASH 4caa44930e5587a0c9914bda9d240acc 2025-09-08 2025-09-26
HASH b9900bef33c6cc9911a5cd7eeda8e093 2025-09-08 2025-09-26
HASH 04b5e068e6f0079c2c205a42df8a3a84 2025-09-08 2025-09-26
HASH 3d6b999d65c775c1d27c8efa615ee520 2025-09-08 2025-09-26
HASH 7967156e138a66f3ee1bfce81836d8d0 2025-09-08 2025-09-26
HASH 77a70e87429c4e552649235a9a2cf11a 2025-09-08 2025-09-26

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Shares tags: T1059.003, T1041, T1071.001 • Published within a month
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