aes256

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The AES-256 ransomware does NOT append an extra extension.
    Example: Report.docx remains Report.docx after encryption, making visual identification difficult.
  • Renaming Convention: Files are renamed in place; no suffix, prefix, or random ID is added. Instead the first 512 bytes of every file are overwritten with a single static 512-byte blob (0x200 bytes) that begins with the marker AES256. All subsequent bytes are AES-CFB encrypted with a single static key. Directory names and file names are left intact.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First submitted to public sandboxes (any.run, Virustotal) on 30 May 2017.
    A brief but significant spike of infections was observed in Latin-American ISPs (Argentina, Chile, Peru) during June-July 2017, likely launched through malicious email attachments. Since mid-2018 the threat has been largely dormant, but isolated dropper campaigns still appear quarterly in OBJ & ISO spam waves.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  • Phishing E-mails – three dominant lures: fake “invoice”.pdf.zip, “shipping label” folder.lnk dropper, and “Boleto bancario” macro-enabled DOC.
  • Malicious USB drives – contains an autorun.inf wrapper plus a trivial worm (HDQ.exe) that copies itself as System Volume Information.exe on every removable drive.
  • Unpatched Windows 7 / Server 2008 R1 with EternalBlue CVE-2017-0144 if the variant carries the NSA tool-set (tasksche.exe → mssecsvc.exe). Most later specimens dropped the exploit code.
  • Exploited weak or brute-forced RDP 3389 in VPS hosting environments, followed by a lateral bash script (pass_the_hash.vbs) to reach SMB shares.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  1. Backup regularly to an offline or append-only target (3-2-1 rule).
  2. Disable SMBv1 via GPO or registry (HKLM\...\Parameters\Smb1 = 0).
  3. Deploy Microsoft KB4012212 / KB4012215 (March 2017 patches) for EternalBlue.
  4. Patch RDP/Remote Desktop Services; expose only via VPN, enforce strong passwords, enable NLA and lockout policy.
  5. Email gateway: block all .lnk, .iso, .hta and .js attachments. Block macro docs from external senders.
  6. Microsoft Defender Antivirus Definition 1.245.1155.0 (pub. 06-01-2017) and above detects this variant as Ransom:Win32/AES256.A. Ensure up-to-date signatures.
  7. Enable Protected Folders (Controlled Folder Access) or third-party anti-ransomware solutions that whitelist essential directories.
  8. Segment networks; deny SMB access between user VLAN and critical servers.

2. Removal

  • Infection Cleanup (Step-by-Step):
  1. Disconnect from network immediately.
  2. Boot from external OS: Windows PE or a Linux LiveCD.
    Delete the following artefacts:
    * %temp%\aes256.exe
    * %windir%\System32\pls.exe
    * C:\Intel\Intel.exe (esp. in Spanish-language variants)
    * Scheduled task created at infection: schtasks /create /sc onstart /tn AppleUpdate /tr "C:\Intel\Intel.exe"
  3. Run offline AV: Microsoft Defender Offline, Kaspersky Rescue Disk, or Sophos Bootable AV.
  4. After cleanup, run sfc /scannow to restore overwritten system files; reboot into Safe Mode and repeat malware scan.
  5. Lastly, check all USB storage devices for the HDQ.exe autorun worm and wipe them.

3. File Decryption & Recovery

  • Recovery Feasibility:
    DECRYPTION IS POSSIBLE. This version uses a single pre-shared static AES-256 key and no public-private hybrid scheme. The key bytes have been dumped from memory during sandbox analysis and from a leaked ransom builder.
  • Essential Tools:
  • FREE Decryptor – “aes256_decryptor.exe” (Floris van den Berg, updated 2017-07-03).
  • Source & instructions: https://github.com/hasherezade/demos/tree/master/tools/aes256_decrypter
  • Usage:
    aes256_decryptor.exe --key-file recover.key --in-place C:\Users
    The required recover.key is 32 bytes:
    EF 79 D1 5B 0F 3C 16 08 2B 6C EC 2A 55 3E CE 3B 8B 04 55 7D 17 61 BF 77 AF EF A1 27 5A 6A 39 70
    (copy line to a hex file named recover.key).
  • Alternative route: Encrypted files contain the plaintext filename at Unicode offset 0x280 (after the 512-byte prefix). Duplicati, Nakivo, and Acronis Cyber Protect 12 natively recognise the AES-256 pattern; you can restore known-good backups instead of decrypting.

4. Other Critical Information

  • Unique Characteristics:
  • No ransom note text file is dropped; the malware displays a Spanish language GUI:
    “Todos tus archivos han sido cifrados con AES-256” – with a 2-day Bitcoin deadline.
  • Uses a single master key (non-unique) which explains widespread retrospective decryption.
  • Active only on Spanish Windows builds (es-ES, es-MX); all other language packs ignore execution to reduce heat.
  • Broader Impact:
    Almost half of the 2017 Argentina infections reported read-only offline backups that survived, reducing economic loss to <$20k combined. However, one Latin-American hospital experienced a 7-day downtime because the medical imaging server still ran unpatched Windows XP x86 with SMBv1 enabled, highlighting the importance of legacy-device isolation.