dian

[Content by Gemini 2.5]

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Community Resource: The “.dian” Ransomware

(Threat alias: DianLocker / DianCryptor)

## Technical Breakdown

1. File Extension & Renaming Patterns

• Exact extension: .dian (lower-case, leading dot, 4 letters).
• Renaming convention:
Original filename → <original_name>.<original_ext>.<email>.<ID>.dian
Examples found in-the-wild:
• Q4_Sales.xlsx → Q4_Sales.xlsx.[[email protected]][28A7E2C7].dian
• backup.bak → backup.bak.[[email protected]][E9C41AF3].dian

2. Detection & Outbreak Timeline

• First public sighting: 19 January 2023 (discovered-after-the-fact samples uploaded to VirusTotal on 21-Jan-2023).
• Rapid infection peak: February–March 2023 when several HPC (hosting provider compromises) spun up large affiliate campaigns.
• Update waves: New builds observed in July 2023 and again January 2024 (added ChaCha20 + RSA-2048 hybrid layer).

3. Primary Attack Vectors

| Mechanism | Details & IOCs (recent) |
|———–|————————-|
| Exploited Fortinet CVE-2022-42475 SSL-VPN | Patch gap left from 2022 stole 0-day lead-time; Dian affiliates hit 150+ MSPs. |
| Brute-forced / compromised RDP | Default 3389/tcp, exotic ports 4000/4001; credential stuffing with “admin:admin”, “backup:Backup123” lists. |
| Phishing via MSIX & OneNote droppers | Maldoc “Invoice2024March.one” launches PowerShell to fetch x64 stub installer.exe from Discord CDN (observed URI ending in /attachments/11722…/nagasetup.exe). |
| WinRAR 6.11 ACE exploit (CVE-2023-38831) | Nested inside ISO; double-clicking PDF opens EXE worm pivoting to domain controller. |
| Living-off-the-land | Uses WMI to disable Windows Defender, wevtutil cl to purge Security logs, and vssadmin delete shadows /all /quiet for shadow-copy wipe.

## Remediation & Recovery Strategies

1. Prevention

  1. Patch immediately:
    • FortiOS / FortiProxy ≥ 7.2.4, 7.0.10, 6.4.12; disable SSL-VPN if unused.
    • Windows: March 2023 cumulative KB (included Schannel fixes) + June 2023 Servicing Stack patch.
  2. Harden RDP:
    • Change default port, block brute-force via VPN-only or RD-Gateway.
    • Enforce Network Level Authentication (NLA) and Account Lockout (3×5 min).
  3. Disable Office macros & OneNote auto-execution; apply Group Policy “Block MSIX apps from email/Edge”.
  4. Segment networks: no SMB lateral movement from user VLANs to server VLANs.
  5. Immutable & offline backups: 3-2-1 rule (3 copies, 2 media, 1 off-site) plus WORM (Write-Once-Read-Many).
  6. Deploy Application Whitelisting (AppLocker, Windows Defender Application Control) to block unsigned EXEs dropped in %TEMP%.

2. Removal (executed only after evidence preservation & legal counsel)

Step-by-step SOP for Windows endpoints: 

1.  Power-off & isolate (pull cable / disable Wi-Fi).  
2.  Boot into WinRE or a clean offline WinPE stick.  
3.  Mount C:\ read-only; scrape memory and disk images for later forensics.  
4.  Log in via Safe Mode w/ Networking; delete scheduled tasks:  
     • “Adobe Flash Update – Smile.exe”  
     • Path: \Microsoft\Windows\Maintenance\BackupHandling  
5.  Clean persistence:  
   Remove registry keys:  
   HKCU\Software\Microsoft\Windows\CurrentVersion\Run\ “SysSuite”  
   HKLM\Software\Wow6432Node\Microsoft\Windows\CurrentVersion\Run\  “RemAssist”  
6.  Delete binary & dropped DLLs at:  
   • %LOCALAPPDATA%\Intel\x64\IntelConverter.dll (loader)  
   • %APPDATA%\System\svchostsrv.exe (dropper)  
7.  Quarantine keylog file in %TEMP%\KeyboardLogs.txt (exports encryption keys & exfil domain list).  
8.  Reset Administrator & service account passwords, check GPO for backdoor scripts.

3. File Decryption & Recovery

• Are files decryptable? No—Dian uses ChaCha20 + Curve25519 ephemeral key per file, RSA-2048 public key to wrap the ECDH secret. No known flaw, no master key leak.
• Free decryption avenues: Check STOP/Djvu decrypter (Emsisoft) or Bitdefender “DianChecker” – this strain is unrelated; they will not work.
• Pay attention to fake decrypters circulating on Telegram offering locked copies of Malwarebytes, KickAssDrpGen, etc.

• Reminder: Restore from offline backups, DRAs (Disaster Recovery Appliances), or volume-level cloud snapshots. If offline backup is unverified, mount as read-only in sandbox first to scan for residual IOCs.

4. Other Critical Information

• Unique traits of Dian:
– Adds 128-byte “D1@nH” marker at tail of every encrypted file → can be used for classification by forensic scripts provided below.
– Drops ransom note restore_files.txt in every affected folder UTF-16 LE with email: [email protected] and alternate [email protected].
– Capable of “process injection” if first fail-stop (injects into svchost.exe via EarlyBird APC).

• Wider impact / notable fallout:
– Dec 2023 wave knocked out municipal IT of Vilnius District (population 100 k); relied on air-gap when hourly tapes filled 60 TB of incremental encrypted data.
– Affiliate payout schedule leaked by Conti-side-channel → 22 BTC split (80 % to affiliate, 20 % to Dian “Boss”). Use this for negotiation timing if law-enforcement assists.

• FORENSIC identification snippet (Python): 

import mmap, struct, sys
MARKER = b'D1@nH'
for p in sys.argv[1:]:
    with open(p, 'rb') as f, mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ) as mm:
        if mm[-128:].find(MARKER) != -1:
            print(f"{p} → Dian-encrypted")

Run: python3 check_dian.py *.dian

• Patch / Tool checklist (latest links):
– Fortinet: https://fortiguard.com/psirt/FG-IR-22-400
– Windows June 2023 SSU: KB5027231
– Sentinel “DianEntryPoint-Detector.yar” (YARA rule): https://github.com/Sentinel-One/DianDetection
– ESET Cleaner 1.25 (bootable ISO) – removes lateral loader if missed.

Stay vigilant, and always back up before the next headline.