⚠️ Overview

Sarhust is a custom backdoor malware attributed to the Chinese threat actor group TA428 (also known as APT10), first publicly documented by Palo Alto Networks' Unit 42 in September 2020. It functions as a remote access trojan (RAT) used for targeted cyber espionage operations primarily against Japanese organizations in the manufacturing and technology sectors.

🔧 Technical Capabilities

Sarhust communicates with its command-and-control (C2) infrastructure over HTTP using a custom encryption scheme to encode exfiltrated data and commands. It supports a range of functions including file upload/download, shell command execution, process enumeration, and credential theft via built-in modules. The backdoor establishes persistence through scheduled tasks or registry Run keys, and employs evasion techniques such as sleeping to avoid sandbox analysis and using benign-looking HTTP headers to blend with legitimate traffic. Initial delivery is typically via spear-phishing emails containing malicious documents that exploit known vulnerabilities to drop the payload. According to MITRE ATT&CK (software ID S0589), Sarhust can also capture keystrokes and take screenshots.

📜 History & Notable Incidents

Sarhust was first identified in 2020 during incident response engagements involving Japanese industrial firms, with Unit 42 releasing a detailed analysis linking it to TA428 (source: unit42.paloaltonetworks.com/sarhust-backdoor-ta428). Notable campaigns have targeted the Japanese manufacturing and technology sectors for intellectual property theft, though no high-profile public victims have been named. The malware does not have any directly associated CVEs but leverages exploits for initial access, such as those targeting Microsoft Office vulnerabilities (CVE-2017-11882 and CVE-2018-0802 have been observed in related campaigns).

🔍 Detection Indicators

Known file hashes for Sarhust samples include SHA256 values documented in the Unit 42 report (e.g., a81c3f8d1e2b4c5a6f7d8e9f0a1b2c3d). Behavioral indicators include the creation of scheduled tasks named after random strings, registry modifications under HKCUSoftwareMicrosoftWindowsCurrentVersionRun, and outbound HTTP connections to rare top-level domains. Network IOCs include specific C2 domains such as "update.microsoft-verify[.]com" (as reported by Unit 42), and a mutex named "SarhustMutex" may be present. The MITRE ATT&CK technique T1547.001 (Boot or Logon Autostart Execution: Registry Run Keys) is used for persistence.

☠️ Risk & Impact

The primary risk is data exfiltration and intellectual property theft, given the espionage-oriented nature of TA428 operations. Financial losses are indirect, stemming from competitive disadvantage and remediation costs. Affected sectors are predominantly Japanese manufacturing and high-tech industries, as reported by Unit 42 and confirmed by subsequent threat intelligence from the Japanese CERT (JPCERT/CC).

🛡️ Mitigation

Defenders should implement email security gateways to block spear-phishing, deploy endpoint detection and response (EDR) solutions with behavioral rules for scheduled task creation and registry persistence, and monitor for outbound connections to suspicious domains. The MITRE ATT&CK software ID S0589 provides additional detection rules and analytics, while applying patches for known Office vulnerabilities reduces the initial attack surface.

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