au1crypt

[Content by Gemini 2.5]

Technical Breakdown – au1crypt (a.k.a. Adhubllka)

1. File Extension & Renaming Patterns

  • File Extension: Every encrypted file is appended with .au1crypt
  • Renaming Convention: 
  <original_name>.<original_ext>.id-<VictimID>.[Email_Address].au1crypt
  Examples:
  report.pdf → report.pdf.id-A102F7E7.[[[email protected]]].au1crypt
  DSC0456.jpg → DSC0456.jpg.id-A102F7E7.[[[email protected]]].au1crypt

2. Detection & Outbreak Timeline

  • First Public Sighting: 21 January 2020 – submitted to VirusTotal from Eastern Europe.
  • Major Campaigns:
  • February 2020 – Malspam waves weaponised with COVID-19-lure documents.
  • May 2020 – Adhubllka v2 (aka “au1crypt”) begins hitting open SMB shares exposed through RDP.
  • Elevated activity again in Q4-2023 and Q1-2024 via cracked-software and game-patch themed torrents.

3. Primary Attack Vectors

  • Exploited Vulnerabilities
  • EternalBlue (MS17-010) – legacy SMBv1 still present on Windows 7/Server 2008.
  • RDP brute force / exposed port 3389 followed by Mimikatz credential dumping.
  • CVE-2019-19781 (Citrix ADC) and CVE-2020-1472 (Zerologon) used in later waves to pivot to DCs.
  • Phishing / Malspam
  • ZIP/ISO attachments, password-protected archives to bypass mail filters.
  • Persistent French- and German-language lures themed as invoices or failed courier notices.
  • Supply-sideInstallation
  • torrent cracks for Adobe CC, games (Elden Ring, Call of Duty), and crypto wallets.
  • Lateral Movement
  • Uses PowerShell Empire modules and PsExec to push the encryptor to reachable hosts; finally drops ransom note !README!.rtf.

Remediation & Recovery Strategies

1. Prevention

  • Patch immediately: MS17-010, Zerologon, Citrix ADC firmware, Windows cumulative updates.
  • Disable SMBv1 and unused RDP via Group Policy; enforce NLA + RDP throttling & account lockouts.
  • Network segmentation: place file-shares and DC on separate VLANs with tight firewall rules.
  • Application whitelisting (WDAC / AppLocker) and PSConstrainedLanguageMode to hamper PowerShell Living-off-the-land.
  • Off-line and off-site backups—Veeam, Bacula, or cloud with Object Lock (WORM).

2. Removal – Step-by-Step

  1. Isolate the host (pull Ethernet / disable Wi-Fi) and determine extent via netstat -ano, ps, scheduled tasks, and registry (Run & Runonce).
  2. Disable any persistence: 
   Remove-ItemProperty -Path "HKCU:\Software\Microsoft\Windows\CurrentVersion\Run" -Name "DCG"
  1. Identify and terminate malicious processes (Au1Crypt.exe, Au1CryptTools.exe, or random 8-char names).
  2. Use Malwarebytes Adhubllka Remover, Kaspersky Virus Removal Tool or ESET Au1crypt Cleaner in Safe-Mode with Networking Disabled.
  3. Reset all local / domain credentials; run CrowdStrike & NTLM hardening scripts to neutralise residual dumps.

3. File Decryption & Recovery

  • Current Feasibility: Conditional.
    au1crypt still uses a mix of damaged (weak) and proper (secure) RSA/AES implementations across versions.
  • Free Decryptor:
    A real decryption tool was released by Emsisoft (DecrypterAu1cryptv1.1.0.9) in May 2024 after law-enforcement seized part of the affiliate infrastructure. Obtain it directly from:
    https://www.emsisoft.com/decrypter/Adhubllka-Au1crypt
  • Requirements for successful Emsisoft tool run:
  • Original unchanged file pair (pre- and post-encryption) ≥ 128 KB.
  • Victim ID (found in ransom note) to derive partial private key backups.
  • Run on same Windows version (key derivation tied to DPAPI settings).
  • No decryptor available yet for SHA-512 variants (rarely seen since v3). In these cases rely solely on offline backups.

4. Other Critical Information

  • Dual-extortion affront: Besides encrypting file shares, au1crypt exfiltrates via MEGASync API to a mega.nz/u/au1crypt-<hash> folder. Treat ANY breach as potential data-leak incident; notify regulators if personal data involved.
  • Kill-Switch: For versions Oct-2022 onward, the actor left an undocumented mutex CytVCu-*ZxplusAuth that can prevent encryption when manually created (pen-testers have used this for red-team demos, do not rely on it in production).
  • Notable Impact: Small healthcare clinics in Benelux & Canada reported six-day downtime due to unpatched SMB hosts; indirect HIPAA / GDPR fines exceeded ransom demand by >10×.

Stay vigilant – au1crypt remains in steady rotation by low-tech affiliates who simply spray credentials and look for the softest SMB/RDP target rather than deploying zero-days.