autolocky

[Content by Gemini 2.5]

Autolocky Ransomware – Community Defense Playbook

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Autolocky exclusively appends the “.locky” extension to all files it encrypts (e.g., Report_2023Q1.xlsx.locky).
  • Renaming Convention: After encryption the malware stores the original file name in cleartext, but rewrites it as <original_name>.<8-hex-chars>.locky (example: Presentation.pptx.AB24F3CA.locky). The random 8-hex value is different for every victim run but does not serve as the encryption key; it is simply an identifier.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First known campaigns began April 2016. Activity peaked during May–June 2016 and declined sharply once public decrypters were released and core C2 infrastructure (ChangeIP, Tor2Web proxies, and Necurs-driven spam) was taken down. Occasional “revival” clusters were still seen Q1-2018 leveraging open RDP, but these instances are now considered sporadic.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Spam Campaigns (90 %) – ZIP attachments containing malicious Office macros (Invoice_[#].docm → macros → PowerShell → Autolocky executable).
  2. Necurs Botnet Secondary Payload – If a machine was already infected with another Necurs family, Autolocky was dropped as a downstream monetization stage.
  3. Exploited RDP – Brute-forced or default-credential RDP sessions later reused by attackers to manually drop the payload (locky.exe).
  4. Server Message Block (SMB) – Rare; few hybrid drops attempted to hit lateral shares via harvested credentials rather than code exploits (no EternalBlue in this variant).

Remediation & Recovery Strategies:

1. Prevention

  • Disable Office macros from internet-originated documents by group policy.
  • Block inbound TCP/3389 (RDP) on perimeter firewalls or place behind VPN + MFA.
  • Decommission SMBv1 on all hosts; enforce SMB signing + network segmentation.
  • Maintain offline, versioned backups (test weekly; 3-2-1 rule).
  • E-mail filtering:
    • Drop any message with .zip containing .exe, .js, .wsf, .scr, or .docm.
    • Expand archives and scan files with at least two AV engines.
  • Application whitelisting (AppLocker / Microsoft Defender Application Control) – explicitly allow only signed binaries.

2. Removal (Verified Workflow)

  1. Physically disconnect the infected machine from all networks.
  2. Boot into Safe Mode with Networking or use a WinPE recovery drive.
  3. Remove scheduled tasks:
  4. Run schtasks /query /fo list | findstr "locky" – delete any syslock, autolocky, or randomized name.
  5. Check Microsoft Sysinternals Autoruns – uncheck and delete executables in:
    • HKCU\Software\Microsoft\Windows\CurrentVersion\Run
    • HKLM\Software\Microsoft\Windows\CurrentVersion\RunOnce
  6. Delete primary payload (often under %TEMP%, %APPDATA%\Roaming, or C:\Users\Public\). Common file names: lk.exe, fe8e36d2.exe, or random 8-hex characters.
  7. Run a full offline scan with Microsoft Defender Offline or Malwarebytes 4.x and quarantine remnants.
  8. Reboot into normal mode; monitor for divergence:
    • If svchost.exe re-invokes PowerShell or rundll32 sending outbound POST to .top domains (beddybeddybeddy.top, breadbreadbread.top), repeat steps 3-5.
  9. When confident the infection is eradicated, restore from offline backups or proceed with decryption.

3. File Decryption & Recovery

  • Feasibility: Free decryptor IS available. Autolocky uses a flaw in the original Locky AES+RSA key-pair generation, making offline master/individual keys recoverable from HKEY_CURRENT_USER\Software\Locky.
  • Essential Tools — Prevention/Remediation:
    • ESET Autolocky Decryptor (signature 2016-08-17, still mirrored at ESET’s support portal).
    • Kaspersky RakhniDecryptor 2023 build also supports Autolocky (hash prefix C6 3C 4F…).
    • Microsoft KB4519998 cumulative patch (Sept-2019) enforces macro group policy restrictions on Office 2016+.
    • Domain GPO template: “Disable VBA for Office applications from the Internet” (Administrative Templates → Word/PowerPoint/Excel Options → Security → Trust Center).

4. Other Critical Information

  • Unique Differentiators:
    • Autolocky reuse of the “Locky” extension and ransom note format (_HELP_instructions.txt) originally led to mis-identification with the Ikustavs-derived ransomware.
    • Internal string “Autolocky” found inside the PE in clear text; static YARA rule:
    rule autolocky { strings: $a = "Autolocky" ascii;$b = "V#&}jYi" wide; condition: all of them }
  • Broader Impact:
    • Caused modest financial losses relative to later Locky iterations (~200 BTC total across all wallets identified).
    • Accelerated adoption of e-mail attachment sandboxing solutions and macro blocking policies worldwide.
    • Indirect consequence: several ISPs started blocking the Tor2Web proxies (.tor2web.org, .tor2web.fi) for dynamic DNS sinkholing.

Final Tip:
Even after successful decryption, keep at least one forensic image of the encrypted volume before you wipe the machine—hash collisions and weak RNGs occasionally reveal multiple valid decryptors over time.