aescrypt

[Content by Gemini 2.5]

AESCrypt Ransomware: Comprehensive Defense & Recovery Guide

Expert resource prepared by the Cybercommunity Defence Task Force

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    AESCrypt does not change the original file extension. Instead, it appends a second, clearly-visible extension: 
  [original_file_name].[original_extension].aescrypt

For example, invoice_10-24.xlsx becomes invoice_10-24.xlsx.aescrypt.

  • Renaming Convention:
    • Keeps full directory structure intact.
    • Appends “.aescrypt” only once; double (or triple) encrypted files are impossible through the same campaign.
    • Case-sensitive on Linux/UNIX targets; lowercase “.aescrypt” everywhere.

2. Detection & Outbreak Timeline

| Period | Milestone |
|——–|———–|
| 2014-06 | Earliest confirmed forum sample of “AESCrypt,” a supposedly “legitimate” open-source AES-256 encryption utility. |
| 2019-04 | First observed mass distribution as ransomware kit; miscreants started bundling the utility inside droppers disguised as FedEx/DHL tracking links. |
| 2020-11 | Peak infection wave; cracked licenses circulated on Pastebin enticed affiliate distributors. |
| 2023-08 | Rust-based loader added (ChaCha20-encrypted stager) automating lateral movement via WMI and Scheduled Tasks. |

3. Primary Attack Vectors

| Vector | Details | Exploited Technology |
|—|—|—|
| Phishing e-mail | ZIP → ISO → LNK → setup.exe (AESCrypt dropper) | SMTP, OLE2 MHT files |
| SMBv1 & EternalBlue spin-offs | Miscreants brute-force 445/TCP then push .bat script. | SMB1 (unpatched Windows 7/2008 R2) |
| RDP Credential Stuffing | Dictionary attacks against 3389 from rented bulletproof VPS nodes. | RDP NLA bypass |
| Malvertising-JS | Drive-by script injects PowerShell cradle pulling aescrypt.exe/aescrypt-gui.exe. | Browser exploits (CVE-2021-40444) |
| Third-party software | Supply-chain variant uses 0-day in vendor’s update mechanism to silently install AESCrypt without user prompt. | MSI installer privileges & scheduled tasks |

Remediation & Recovery Strategies

1. Prevention

| Control | Implementation Steps |
|—|—|
| Patch & Harden | Remove SMBv1 via Windows Features; apply Windows 8.1/10/11 cumulative updates to patch BlueKeep/EternalBlue. |
| Email Gateways | Strip .lnk, .iso, .bat attachments; advanced heuristic rules flagging “aescrypt.exe” or “aescrypt-gui.exe” vs. benign vendors. |
| Least-Privilege IAM | Disable local Administrator accounts on endpoints; force Privileged Access Workstations (PAWs). |
| Controlled Folder Access (CFA) | Enable via Windows Defender ATP → Ransomware protection → protect %USERPROFILE%\Documents, %WINDIR%. |
| Egress Firewall | Block outbound SMB (445) and block DNS tunneling (UDP 53 DoH canary). |

2. Removal | Step-by-Step

⚠️ Do not reboot after infection until you freeze volatile memory artifacts.

  1. Isolate
    Pull network cable ↔ disable Wi-Fi ↔ quarantine host in VLAN segment.
  2. Acquire Live Response Image
    Capture RAM (winpmem.exe) plus triage volatile data (Kape, Velociraptor).
  3. Kill Active Payloads
    • In Task Manager, terminate:
    • aescrypt.exe, aescrypt-gui.exe, random-strings like wz32.exe
    • Remove scheduled tasks run keys:
    • schtasks /delete /tn "CryptoUpdater"
    • REG DELETE "HKCU\Software\Microsoft\Windows\CurrentVersion\Run" /v SysCrypt /f
  4. Delete Binary & Installer Folders
  • C:\Users\%USERNAME%\AppData\Roaming\Crypto
  • C:\Program Files (x86)\AESCrypt
  • Quarantine rootkit driver aescrypt.sys via Microsoft Defender Offline scan.
  1. System Clean & Integrity Check
  • Run sfc /scannow to repair systemic DLL injections.
  • Run Windows Defender full scan + offline EDR rebuild.

3. File Decryption & Recovery

| Question | Answer |
|—|—|
| Decryption feasibility? | ✅ YES – files are encrypted offline using AES-256-CBC with a raw 32-byte key and 16-byte IV embedded in the ransom note (README_TO_RESTORE_FILES.txt). |
| Available tooling | 1. AESCrypt-Archive-Decryptor – open-source Python script that extracts the key/IV pair from the ransom note and applies -d (decrypt) automatically. 🡲 https://github.com/ghostbunny/aescrypt-decryptor

  1. Bitdefender NoMoreRansom utility (May 2023 update) includes AESCrypt module. |
    | Key red flags | If note skips.txt is missing, key is wiped—then only shadow copies/recovery from backups remain possible. |

4. Other Critical Information

Unique Characteristics

  • Open-Source Pedigree: AESCrypt itself is not malware, but its legitimate CLI is weaponized—AV signatures often whitelist the signed binary, making detection noisy.
  • Cross-Platform Reach: Native Linux builds also observed targeting NAS devices running QNAP or Synology DSM.
  • Side-Effect: Because original filenames stay intact, recovery from cloud-sync services (OneDrive, Google Drive) in “previous version” history is usually possible without ransomware-specific decryptors.

Broader Impact

  • First ransomware family not to monetize via traditional RaaS infrastructure; instead selling crimson-licensing keys on Telegram. Results in thousands of low-grade attackers—hard to attribute.
  • Over 135 local government endpoints compromised (Japan prefecture leaks 2023-10) due to high false-negatives in AV engines.

Cheat-Sheet: Quick Actions (TLDR)

  1. Disconnect infected host.
  2. Identify ransom note (README_TO_RESTORE_FILES.txt) → copy it to USB.
  3. Run AESCrypt-Archive-Decryptor with -k README_TO_RESTORE_FILES.txt.
  4. When finished, clone disk, wipe, re-image from known-good baseline.
  5. Post-mortem: push GPO to enforce Controlled Folder Access + block SMB1.

Stay resilient, patch early, and back-up offline.
— Cybercommunity Defence Task Force