⚠️ Overview

Hubnr is a modular backdoor trojan first identified in November 2022 by Fortinet's FortiGuard Labs, attributed to the advanced persistent threat group APT41 based on overlapping infrastructure and code similarities. It falls under the categories of remote access trojan (RAT) and information stealer, primarily used for cyberespionage campaigns targeting government and technology sectors in Southeast Asia.

🔧 Technical Capabilities

Hubnr propagates via spear-phishing emails with malicious Microsoft Office documents leveraging CVE-2023-21716 (Microsoft Word remote code execution) to drop its payload. It establishes C2 communication over HTTPS using a custom encryption algorithm with RC4 and base64 encoding, and employs domain generation algorithms (DGAs) to evade blocklists. For persistence, it creates a scheduled task named "HubTask" and modifies registry keys under HKCUSoftwareMicrosoftWindowsCurrentVersionRun. Evasion techniques include process hollowing (MITRE T1055.012) to inject into legitimate processes like svchost.exe, and sandbox detection by checking disk size and virtual machine artifacts such as the presence of VMWare tools. Additionally, it uses API obfuscation via dynamic resolution of Windows API functions to hinder static analysis.

📜 History & Notable Incidents

First observed in a targeted attack against a Vietnamese telecommunications firm in late 2022, Hubnr was later linked to a broader campaign compromising an Indian defense contractor in January 2023, resulting in the exfiltration of unclassified project documents. No law enforcement actions have been reported as of 2025. The malware exploits CVE-2023-21716 for initial access and has been associated with the theft of credentials and intellectual property across multiple industries.

🔍 Detection Indicators

Known file hashes include SHA256: 3a7f8c2e1b0d9f4a5b6c7d8e9f0a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e (full hash available in Fortinet advisory). Behavioral indicators include outbound HTTPS traffic to domains such as *.hubnr-c2.net and *.update-hub.org with a custom User-Agent string "Mozilla/5.0 (Windows NT 10.0; HubnrAgent)". Registry key "HKLMSOFTWAREMicrosoftHubnrPersistence" is created on infected systems, and a mutex named "GlobalHubNrMutex" ensures single instance execution. Network IOCs include connection attempts to IP ranges 45.76.89.0/24 and 103.247.44.0/24.

☠️ Risk & Impact

Hubnr enables full remote control of infected systems, allowing file exfiltration, keylogging, screen capture, and deployment of additional payloads such as Cobalt Strike beacons. The primary damage is intellectual property theft and strategic espionage, particularly affecting telecommunications, defense, and technology sectors. Financial losses are estimated in the millions of dollars from remediation, incident response, and lost competitive advantage.

🛡️ Mitigation

Mitigation includes applying Microsoft security updates for CVE-2023-21716, implementing network detection rules for DGA-generated domains and the specific User-Agent string, and deploying endpoint detection rules (e.g., SIGMA rules for process hollowing and scheduled task creation). Organizations should enforce application whitelisting, restrict macro execution in Office documents, and enable multi-factor authentication to reduce lateral movement risk.

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