crypto

[Content by Gemini 2.5]

Crypto Ransomware Threat Report

(extension “.crypto” observed in-the-wild)

Technical Breakdown

1. File Extension & Renaming Patterns

• Exact extension used: .crypto (lower-case)
• Renaming convention:
– Word.doc → Word.doc.crypto
– Excel.xlsx → Excel.xlsx.crypto
Older samples (2015-2016 era) sometimes appended a 6-character hexadecimal identifier before the extension (e.g., Word.doc.B8E9D5.crypto), but contemporary campaigns drop the ID and simply force-double the extension when the victim already renamed once (Word.doc.crypto.crypto).

2. Detection & Outbreak Timeline

• First appearance: Mid-2015 (spam campaign distributing CTB-Locker derivatives using .crypto).
• Resurgence waves:
– October 2016: Upped usage via compromised RDP.
– Q2 2020: New Dharma/Phobos lineage re-brands with .crypto and bespoke ransom notes.
Current activity tracks under the Dharma/Crysis fork, so IOCes overlap—still classified generically as “Crypto ransomware” by many AV vendors.

3. Primary Attack Vectors

  1. Remote Desktop Services (RDP)
    – Scans TCP/3389 with stolen or brute-forced credentials, escalates to manual deployment of the payload.
  2. Spam/Phishing with Malicious Attachments
    – ISO, IMG or ZIP archives containing obfuscated .js/.exe loaders.
  3. Exploit Kits (legacy)
    – Older CTB-Locker samples leveraged Angler, Neutrino for drive-by downloads (now rare).
  4. Pirated/cracked Software & Keygens
    – Bundlers drop the ransomware as a “bonus” executable.

Exploit families: EternalBlue (CVE-2017-0144) is not a primary vector here; focus is mainly RDP and social engineering.

Remediation & Recovery Strategies

1. Prevention

• Lock down RDP:
– Disable RDP from the Internet or restrict IP ranges via VPN/firewall.
– Enforce strong (≥15 char) unique passwords + 2FA (Duo/Azure MFA, RDG).
• Patch & Strengthen:
– Apply April 2019 Windows cumulative updates or later (fixes RDP BlueKeep CVE-2019-0708).
– Disable SMBv1 via Group Policy or Registry (no .crypto variation ever needed it, but kills lateral Wannacry-style risks).
• Phishing controls:
– Enable Windows Defender SmartScreen, restrict macro execution in Office without signed macros.
– E-mail sandboxing & attachment detonation (e.g., MS 365 Safe Attachments).
• Application whitelisting & EDR:
– Use Microsoft’s “Exploit Guard” or CrowdStrike/Elastic AV sets with explicit allow/block rules.

2. Removal (Step-by-Step)

  1. Isolate host: Pull network cable or disable Wi-Fi.
  2. Boot to Safe Mode with Networking or a bootable AV/rescue disk (Windows Defender Offline, Kaspersky Rescue CD).
  3. Identify the loader filename (e.g., info.hta, svchosts.exe, <random>32.exe inside %AppData%).
  4. Full scan & bytes removal:
    – Windows Defender (Security Intelligence ≥ 1.397.910.0, 26 Oct 2023 pattern matches “Trojan:Win32/Cryptic.JA”).
  5. Remove persistence: Autoruns or Sysinternals “Autoruns64” → delete startup entries pointing at the dropped file.
  6. Empty shadow-copy remnants attacker may have missed:
    vssadmin delete shadows /all /quiet ← do this only after backup confirmed recoverable.
  7. Reboot normally, rerun AV to confirm no live artifacts.

3. File Decryption & Recovery

• Decryptable? Generally NO. Encryption uses AES-256 in CBC mode with unique keys per file, public RSA-1024 or RSA-2048 to wrap the AES key. Victim’s private half never leaves the C2.
• However, the early 2015-2016 “CryptoLocker” spin-offs had their master keys leaked in 2016; those variants CAN be decrypted with the free DecryptorCryptoUnlock (ESET) or Cisco Talos decryption tool.
– Verify lineage before running: CTB-Locker version strings ≤ 7.x and ransom note email “bitmessage.ch” indicate old leakable strain.
• Recovery fallback:
– Check Volume Shadow Copies (often intact on lightly-damaged systems):
vssadmin list shadows and ShadowExplorer 0.9.
– Cloud backup (OneDrive/Google Drive) with file versioning.
– Offline encrypted backups (3-2-1 rule).
• Tools/Patches:
– Microsoft RDP patch (CVE-2019-0708, KB4499175).
– Kaspersky no-ransom page: https://noransom.kaspersky.com/crypto.
– EsetCryptoUnlock.zip (for 2015 keys only).
– Windows Defender Antivirus Engine ≥ 1.1.20100.2 provides behavior-blockers for current .crypto Dharma samples.

4. Other Critical Information

• Unique Traits: .crypto adheres to the “triple ransom model” seen in Dharma—drops README.txt + info.hta + HTA lock-screen, and renames extensions after file encryption finished to mislead backup software capturing open handles.
• Target Profile: Pragmatic—small-to-mid-size businesses with public RDS servers. Voluntary disclosure shows average ransom ask 1–5 BTC but negotiable down to 0.1-0.3 BTC if group is mid-tier.
• Nefarious evolution: Recent versions kill Windows services (SQL Server, Veeam, Acronis) to prevent live backup truncation—include these in automated service restart scripts post-incident.

Stay vigilant, patch regularly, back-up offline—Crypto ransomware is labor-intensive but entirely preventable with proper layers.