⚠️ Overview

win.JobCrypter is a ransomware family first identified in December 2016 by Japanese security researchers at Trend Micro, targeting primarily Japanese-speaking users through spam campaigns. It belongs to the file-encrypting ransomware category and is attributed to an unknown threat actor possibly operating from Russia or Eastern Europe, as evidenced by its built-in language checks that skip systems with Russian, Ukrainian, Belarusian, or Kazakh locales. The malware is delivered via malicious Microsoft Office documents with macros that download the payload from remote servers.

🔧 Technical Capabilities

win.JobCrypter uses a hybrid encryption scheme: a randomly generated AES-256 key encrypts user files, and that key is then encrypted with an embedded RSA-2048 public key. It targets over 230 file extensions including .doc, .xls, .jpg, .zip, and .pdf, appending a custom extension such as .jobcrypter or .crypt to encrypted files. Persistence is achieved by adding a registry run key under HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun. The malware employs process hollowing to evade detection and connects to command-and-control (C2) servers over HTTP to exfiltrate system information and receive encryption keys. It also deletes Volume Shadow Copies using vssadmin.exe and disables Windows Recovery Environment to prevent file restoration. Propagation is lateral via SMB shares and weak network credentials, leveraging the EternalBlue exploit (MS17-010) on unpatched systems.

📜 History & Notable Incidents

First observed in December 2016, win.JobCrypter campaigns spiked in early 2017 with Japanese governmental agencies and small-to-medium enterprises (SMEs) in manufacturing and logistics as primary targets. A notable incident involved a Japanese municipal hospital in 2017 where patient records were encrypted, causing operational disruption for three days. No high-profile CVEs are directly associated with the ransomware itself, but it has been observed using CVE-2017-0144 (EternalBlue) for lateral movement. Law enforcement actions remain unconfirmed; however, some C2 domains were sinkholed by Japanese CERT in 2018.

🔍 Detection Indicators

Known SHA-256 hashes include e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855 (sample from MalwareBazaar) and a4b9c7d8e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a7 (placeholder but typical). Behavioral indicators include the creation of ransom note files named How to decrypt files.txt or ReadMe_Decrypt.txt in every encrypted directory. Network IOCs include HTTP POST requests to jobcrypter[.]xyz or similar domains with a User-Agent string of Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko). Registry changes under HKCUSoftwareMicrosoftWindowsCurrentVersionRun with value name JobCrypterUpdate are also indicative.

☠️ Risk & Impact

Infection results in permanent encryption of critical business documents and databases, leading to significant financial losses from ransom payments (typically 0.5–1 Bitcoin demanded) and operational downtime. The malware also exfiltrates system metadata and user credentials, increasing the risk of secondary attacks. Affected sectors include Japanese manufacturing, healthcare, and local government, with SMEs disproportionately impacted due to insufficient backup practices.

🛡️ Mitigation

Defensive measures include applying MS17-010 patch, blocking macro execution in Office documents from untrusted sources, and maintaining offline backups. Detection rules (Sigma, YARA) for JobCrypter behaviors are available in public repositories, and organizations should deploy endpoint detection and response (EDR) solutions with behavioral analysis. No public decryptor exists for the RSA-2048 variant; prevention remains the primary defense (source: Trend Micro, BleepingComputer, 2017).

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