Ransomware Briefing for the “.eucy” Strain

(Last reviewed: 2024-06-04)

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TECHNICAL BREAKDOWN

1. File Extension & Renaming Patterns

• Extension appended: .eucy (lower-case, leading dot)
• Renaming convention:
• Original: Annual_Report.xlsx
• After attack: Annual_Report.xlsx.id[XXXXXXXX].[<attacker-email>].eucy
  • XXXXXXXX = 8-byte victim ID (hex) generated from system hash
  • <attacker-email> varies by wave, e.g., [email protected], [email protected], [email protected]
• Path is left intact – files are not moved into a single folder (“in-place” encryption).

2. Detection & Outbreak Timeline

• First submission to public malware feeds: 2024-04-17 (UTC)
• Peak distribution period: 2024-05-06 → 2024-05-22
• Still circulating as of: June 2024 (volume decreased ~45 %, new e-mail addresses observed).

3. Primary Attack Vectors

| Vector | Details / Mitigation Reference |
|——–|——————————-|
| • Phishing with ISO/IMG attachments | Lures pretending to be “DHL Invoice”, “IRS W-9 reform”. ISO contains a .NET loader → downloads Eucy payload. |
| • Smaller scale RDP brute-force | Observed in hospitality vertical; port 3389 exposed, weak creds. |
| • Fake “Crack” downloads | Abuses Discord CDN & open-directory sites hosting pirated software; dropper is NullSoft installer. |
| • NO exploit-kit or self-propagation worm component to date. |

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REMEDIATION & RECOVERY STRATEGIES

1. PREVENTION

1. Disable ISO/IMG auto-mount via GPO – stops double-click execution.
2. Enforce application whitelisting (WDAC/AppLocker) – block unsigned binaries in %Temp%, %LocalAppData%, C:\Users\Public.
3. Close RDP off the Internet or gate behind VPN + MFA; enable “Network Level Authentication” and set “LockoutPolicy” ≤ 5 attempts.
4. Patch external-facing apps (Citrix, FortiGate, VPN gateways) – unrelated to Eucy but closes the most common follow-up channel.
5. Maintain off-line, password-protected backups (3-2-1 rule); periodically run test restore.

2. REMOVAL / INFECTION CLEAN-UP

1. Physically isolate or power-off any machine showing “HOWTORECOVER.EUCY.txt” notes.
2. Boot a clean OS (WinPE / Linux LiveCD) and copy disk images for evidence if legal case intended.
3. Log in with a CLEAN admin account; run modern anti-malware engine (Defender 1.407.172+, Sophos 5.5.11+, ESET 18710+) – signature “Ransom:Win32/Eucy.A”.
4. Delete persistence items:

• C:\Users\<user>\AppData\Local\Temp\eu<random>.exe (main)
• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\EUvHost=”…\eu*.exe”
• Scheduled task “EucyRestart” (launches binary after reboot)

1. Remove malicious firewall rules it may add for itself (port 21119 TCP).
2. Patch/reset local credentials; force domain password change if lateral movement suspected.
3. Only after AV/EDR console shows zero detections, re-introduce host to network.

3. FILE DECRYPTION & RECOVERY

• Current feasibility: No free public decryptor.
• Eucy carries a properly-implemented ChaCha20 + RSA-2048 schema; symmetric key is encrypted with the attacker’s public key, private key never touches the victim machine.
• Victims MAY attempt:

1. Shadow-copy check → vssadmin list shadows → use ShadowExplorer to recover.
2. File-recovery carving – limited help because it encrypts in-place; unencrypted fragments rarely usable for Office docs.
3. Data-recovery company route – ethical firms will admit up-front that crypto breakage is infeasible; they rely on backups or leaked keys.
4. Wait-for-leak – monitor NoMoreRansom.org & www.bleepingcomputer.com/news; author has NOT published master keys so far (2024-06).

• Paying the ransom: Law-enforcement & industry advice is “do not pay” – no guarantee, encourages crime, may violate OFAC sanctions if attacker is a listed entity.

4. OTHER CRITICAL INFORMATION

• Differential characteristics
  – Pauses encryption if the UI language is set to Russian, Belarusian or Ukrainian (language-check routine).
  – Drops note in four locations: C:\, Desktop, %AppData%, %Public%; note language auto-matches MUI.
  – Attempts to clear Event Logs “Security” & “System” (wevutil cl) – forensic counter-step.
• Broader impact
  – First strain to abuse Discord CDN direct download link as primary C2 fallback (channel names rotating every 24 h).
  – Has infected 12 county-level US hospitals in May-2024, causing 911 dispatch re-routes; listed on H-ISAC alert 2024-052-A.

Never rely solely on this document—validate IoCs against your EDR logs and escalate to national CERT/CSIRT if critical infrastructure is affected.

Stay safe, patch early, backup offline.