APT37: Rust Backdoor & Python Loader
2025-09-08 • Zscaler •
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 |