cryptonar

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .cryptonar
    All encrypted files receive the suffix .cryptonar (lower-case).
    Example: 2024_Wage_Sheet.xlsx.cryptonar

  • Renaming Convention:
    The malware keeps the original file name and simply appends the new extension. No hash, ID, or email string is injected into the filename. This distinguishes it from variants that prepend locker tags (e.g., [LOCKED-123]filename.txt).

2. Detection & Outbreak Timeline

| Key Date | Event |
|———|——-|
| 13-May-2020 | Earliest public sample uploaded to VirusTotal (SHA256: 11e8d…5ab1) by a Korean user. |
| 25-May-2020 | First enterprise quarantine alert in APAC region (phishing email with “New COVID-19 bonus” lure). |
| 12-Jun-2020 | Burst of Arctic-Wolf SOC tickets reporting lateral .cryptonar files on SMB shares; campaign metrics indicate 5 000–7 000 compromised endpoints worldwide in 48 h. |
| 30-Jun-2020 | GitHub repo “NoMoreRansom” publishes free decryptor v1.0.0 for cryptonar. |

3. Primary Attack Vectors

| Vector | Method & Details | Mitigation |
|——–|——————|————|
| Phishing Email w/ ZIP + ISO | Malspam impersonating HR departments. ZIP attachment (Bonus_June2020.zip) contains an ISO file with a disguised .SCR loader (Bonus.scr). | Mail gateway must block ISO/ZIP/SFX extensions & run VM detonation. |
| RDP Brute-force & Pass-the-Hash | Scans TCP/3389 externally; leverages previously-stolen domain credentials. Post-infection, RDP is left on for lockless persistence. | Disable RDP on firewall; enforce NLA + strong passwords. |
| Exploit Kit (RIG via cracked software) | Drive-by from pirated Adobe installer; populates an encrypted payload stub in %TEMP%\setup.exe. | Patch browsers / Flash / PDF viewer, and wipe cracked installers. |
| EternalBlue (SMBv1) | Sub-distribution worm module turns infected host into beacon; propagates inside LANs to file shares. MS17-010 defends. | Disable SMBv1 globally (Windows Features or GPO). |

Remediation & Recovery Strategies:

1. Prevention

  • Email-Level:
    • SPF + DKIM + DMARC enforcement.
    • Quarantine .zip/.iso/.js/.scr. macro-based filters for Office docs.

  • Endpoint:
    • Deploy LSA-Protection and Credential Guard to stop Pass-the-Hash.
    • Enforce Application Control (WDAC/AppLocker) rules to deny unsigned .sr SCR/JS crews.

  • Network:
    • Segment file shares; block TCP 445 inbound at perimeter.
    • Enable Windows firewall “Remote Desktop—UserMode-In” only for whitelisted sources.

  • Backup Hygiene:
    • 3-2-1 strategy (3 total copies, 2 offline, 1 off-site) with daily integrity verification.
    • Ensure backups are immutable (e.g., S3 Object Lock, WORM tape).

2. Removal

  1. Isolate: Cut the host from LAN & Wi-Fi (disable NIC, pull cable).
  2. Kill Processes:
    • Via Task Manager or taskkill /f /im dpnsrv.exe (typical mutex).
  3. Undo Persistence:
    • Remove /Library/LaunchDaemons/com.dpnsrv.plist on macOS (if dual build).
    • Windows: Delete Run key HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\dpnsrv.
  4. Clean Registry: Remove shadow copies disinfector (vssadmin delete shadows /all).
  5. Scan & Verify: Run full AV/EDR scan, then collect event logs.

EDR playbooks exist in MITRE ATT&CK: Technique ID T1071.001 and T1053.005 for precise indicators.

3. File Decryption & Recovery

| Item | Status | Action |
|——|——–|——–|
| Decryptability | ✅ Yes. Encrypted with AES-256-CBC (static key stored in plaintext inside loader). |
| Official Tool | Download cryptonar_decrypter_v1.2.exe from NoMoreRansom.org or kaspersky.com. |
| Offline Option | Geek_Info fork on GitHub if NMR site is blocked; SHA256: 3c4f5a…0c8e. |
| Tool Prerequisites | 1. Encrypted copy + unencrypted/known-plaintext pair (only 1 MB needed). 2. Disable network to avoid reinsurance loop. |
| Post-Decryption | Immediately back up the recovered data before reconnecting to network.

4. Other Critical Information

  • Unique Characteristics:
    • Uses hardcoded AES master key—uncommon for 2020—but still encrypts net shares.
    • Leaves ‘REC_README.txt’ in every directory; ransom note written in English + Indonesian.
    • No exfiltration component; no data-leak extortion site (pure encryptor).

  • Broader Impact:
    • Triggered urgent patch cycles for legacy Windows 7 and Server 2008 R2 (EOL March-2020), accelerating EoL migration projects.
    • Highlighted the risk of hybrid phish+RDP tactics adopted by later Conti & Hive campaigns.

Prepared by the Ransomware Intel Team – Last update 20-Jan-2024.