⚠️ Overview

Samurai is a custom backdoor malware first documented by FireEye in 2018, attributed to the North Korean state-sponsored Lazarus group (APT38). It functions as a remote access trojan (RAT) targeting cryptocurrency exchanges and financial institutions in Asia and Europe.

🔧 Technical Capabilities

Samurai communicates over HTTP using RC4 encryption with a fixed key derived from a hardcoded string. Persistence is achieved via a registry run key under HKCUSoftwareMicrosoftWindowsCurrentVersionRun named “Samurai”. It employs process hollowing into svchost.exe and API hooking for keylogging and screen capture. Propagation uses spear-phishing emails with Office documents exploiting CVE-2017-11882 and CVE-2018-0802. The backdoor supports file upload/download, command execution via cmd.exe and PowerShell, clipboard monitoring, and lateral movement using Windows Management Instrumentation (WMI). It performs anti-analysis using IsDebuggerPresent and virtual machine detection via firmware queries, and uses a domain generation algorithm for backup C2 domains often hosted on compromised WordPress sites.

📜 History & Notable Incidents

First identified in early 2018, Samurai targeted South Korean cryptocurrency exchanges via malicious HWP documents and also compromised a South Korean bank to steal customer data. In 2020, a variant attributed to the BlueNoroff subgroup attacked a Polish exchange, exfiltrating wallet files and stealing an estimated $8 million in cryptocurrency. A 2021 campaign used Samurai against a Japanese bank, employing a custom exploit for an old document viewer. BlueNoroff is a Lazarus subgroup focusing exclusively on financial cybercrime.

🔍 Detection Indicators

Known file hashes include MD5 e6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1 and SHA256 a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3. Behavioral indicators include the mutex GlobalSamuraiMutex, registry run key, and a scheduled task named ‘SamuraiUpdate’. Network indicators include HTTP POST to “/gate.php” with User-Agent Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2490.71 Safari/537.36, and C2 domains ending in .xyz or .top. A dropped file samsrv.dll is placed in the %Temp% directory.

☠️ Risk & Impact

Samurai exfiltrates wallet private keys, credentials, and clipboard data to redirect cryptocurrency transactions, often over HTTPS to evade detection. The 2020 Polish exchange incident caused $8 million in direct theft. The malware targets wallet applications like CoinMiner and Electrum, enabling fund theft during transactions. Long-term espionage compromises operational security, and data breaches lead to reputational damage and regulatory penalties for affected firms.

🛡️ Mitigation

Implement email security gateways to block spear-phishing, patch Microsoft Office against CVE-2017-11882 and CVE-2018-0802, and deploy endpoint detection rules for the mutex, registry key, scheduled task, and specific User-Agent. Use YARA rules to detect “Samurai” strings in artifacts. Apply network segmentation, monitor process injections via Sysmon, and conduct regular threat hunting with EDR behavioral analytics.

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