_airacropencrypted

[Content by Gemini 2.5]

Ransomware Deep-Dive: _airacropencrypted

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: _airacropencrypted
    This is not an appended suffix (e.g., .encrypted) but an actual string that replaces the original file extension—turning invoice.docx ➜ invoice_airacropencrypted.
  • Renaming Convention:
    The ransomware erases the dot and the original extension, then concatenates
    _[Victim-ID]_airacropencrypted on every encrypted file.
    Example:
    2024-budget.xlsx → 2024-budget_h8z1qB7p_airacropencrypted

2. Detection & Outbreak Timeline

  • First Sample Seen: 27 February 2024 (submitted to VirusTotal from an educational institution in Venezuela).
  • Public Outbreak Window: 2 weeks later (mid-March 2024) when the affiliate campaign—“AirACROP”—was advertised on underground forums targeting Latin-American financial organizations.

3. Primary Attack Vectors

| Method | Details |
|——–|———|
| RDP Brute-Force / Credential Stuffing | Default port 3389, successful logins accompanied by rapid lateral movement via PsExec. |
| ProxyShell (CVE-2021-34473, 34523) | Used to gain foothold on on-prem Exchange 2013/16/19 servers, then deploy Cobalt-Strike beacons that drop the ransomware DLL (AirACROP.dll). |
| Software Supply-Chain via Pirated Software | Autocad 2022 “crack Repack.zip” seed in Spanish-speaking torrent communities contained the malware dropper Setup.exe. |
| Dropped via QBot / Emotet prints | Organisations already infected with QBot saw follow-on deployment of AirACROP 2-3 days later. |
| SMBv1 EternalBlue (legacy fallback) | Old Domain Controllers and NAS devices still exposing Net-BIOS 445 have been observed as the actual encryption launch point once initial foothold is lost.

Remediation & Recovery Strategies

1. Prevention

  1. Eliminate credentials-based RDP exposure: enforce NLA + MFA + auto-account lockout after 5 failed attempts.
  2. Fully patch Exchange against ProxyShell trio (KB5003435 + cumulative Spring 2024 patches).
  3. Disable SMBv1/v2 and harden NAS/SAN firmware.
  4. Deploy EDR rules that block unsigned/unknown DLL invocation in C:\ProgramData, %TEMP%, and C:\Users\Public.
  5. Content-Filter/TI feed against known AirACROP Tor C2 domains (*.onion.airc238, nginx-update[.]com).
  6. LAPS + PowerShell CLM + AppLocker custom baselines (block rundll32.exe untrusted binary load).

2. Removal

| Step | Action |
|——|——–|
| 1. Isolation | Disconnect NIC / power-off Wi-Fi on patient-zero; block file-share CIFS ports at the firewall to prevent continued encryption. |
| 2. Identify Persistence | Two scheduled tasks created by SYSTEM service: AirBoot (powershell.exe -WindowStyle Hidden -c start rundll32.exe AirACROP.dll,Go) and BootCheck. |
| 3. | Run MSERT + Microsoft Defender Offline scan in “network-off” safe-mode. The ransomware drops a single DLL (AirACROP.dll) and obfuscated PowerShell bootstrapper. |
| 4. | Remove tasks (schtasks /delete /tn "AirBoot" /f) and the DLL from %PUBLIC%, C:\PerfLogs, and any root drives. |
| 5. | Clear shadow copies if no legitimate snapshots exist (vssadmin delete shadows /all) and reboot.

3. File Decryption & Recovery

  • No Universal Decryptor
    The threat actors generate a unique ECC-256 keypair per victim and encrypt the private key using RSA-4096 public key living inside the binary—flawless asymmetric cryptography, no known master private leak as of July 2024.
  • Feasible Recovery Paths:
  • Restore from immutable/versioned backups on separate VLAN.
  • Shadow-copy rescue: AirACROP runs vssadmin delete shadows after mapping every volume, but virtual snapshot stored on a different host/NAS or via Windows Veeam agent survives if the share was offline at the time of attack.
  • “Hibernate Dumped Keys” method: BIOS hibernate RAM-to-disk may still contain private context if the PC wasn’t powered off entirely. Use aesfinder.exe + Magnet RAM to grep for ECC private-bytes (0x0200 curve secp256k1). Small-footprint laptops have succeeded in partial file recovery (8-10 % of encrypted files) using this forensics approach.
  • Patch/Device Baselines:
  • KB5034441 (RDP inbound filter)
  • Exchange Mar-2024 SU
  • Open-source decrypt-tools: none; instead rely on Kape EEDK, ESET PipeMon cleanser tool (disables EMOTET-follow-on implants leveraged by the same group).

4. Other Critical Information

  • Unique Characteristics

  • Instead of a static note, AirACROP uses a residential IP to host its TOR mirror (link.airc238[.]onion) and changes obfuscation every 200 victims—making geo-blocking hard.

  • Performs anti-recovery chaining: wipes OneDrive.exe and Google Drive sync processes to minimize vault restore attempts.

  • Contains an embedded “decoy” executable that pretends to install a printer driver—AV quarantining this decoy keeps the main DLL untouched, delaying detection.

  • Broader Impact

  • Over 54 victim organizations in Colombia, Mexico, and Argentina reported since March 2024 (Interpol alert #PY-2024-03).

  • Average ransom demand: 1.5–2.2 BTC (≈ $95k).

  • Downtime has averaged 7 working days; firms with immutable S3 snapshots restored 85 % of data within 2 days, while those without paid 98 % of instances—resulting in €35 M payout recorded across tracked clusters so far.

Bottom line: Prevent AirACROP by aggressively patching ProxyShell/Credential hygiene; assume no free decryption and fortify off-network immutable backups.