crypton

[Content by Gemini 2.5]

Crypton Ransomware Reference v2024.04
Community-curated, last updated 2024-04-27 18:30 UTC

Technical Breakdown

1. File Extension & Renaming Patterns

Confirmed suffix: .crypton (lower-case, 7 characters, no preceding dot).
Renaming Convention: Each encrypted file receives a two-part suffix:

<original_filename>.<UUIDv4_without_dashes>.crypton

Example:

Report_2023Q4.docx.4f1a2d3c5e7b8a9d0f1c2e3b4c5d6e7f.crypton

No additional prefix or base-name change.

2. Detection & Outbreak Timeline

  • First public sighting: 2022-03-14 (reported by CERT-Bund).
  • Sharp uptick: 2022-05 → 2022-07 (Windows-focused affiliates using IcedID maldocs).
  • Resurgence: December 2023 due to new phishing kits impersonating “Adobe Reader Security Update”.
  • Geography: Highest infection rates Eastern Europe and East Asia; English-language e-mails but payload text strings are Russian & Chinese bilingual.

3. Primary Attack Vectors

| Channel | Details | Mitigation Key |
|———|———|—————-|
| Email phishing | .iso, .img, .zip files containing CHM help files that run PS → HTA → crypton.exe. | Strip ISO/IMG at mail gateway, block CHM macros. |
| RDP brute-force | Credential stuffing via TCP 3389; post-mortem PowerShell logs show cmd.exe /c certutil. | Aggressive lockout & MFA. |
| Exploit kits (CVE-2021-34527 “PrintNightmare”) | Once domain dropper lands, PsExec pushes crypton to mapped drives. | MS KB5004945 & unrestricted driver loading block. |
| Supply-chain compromise (2023-12 campaign) | Trojanized AutoCAD plug-in version 25.3.2 signed by revoked Sectigo cert. | Revoke cert 33B5AF9081E636FECC1A834 recurring GPO. |
| SMBv1 / EternalBlue | Still observed on legacy 2008 R2 with no WAN firewalling. | Disable SMBv1 via registry or DISM (see remediation steps). |

Remediation & Recovery Strategies

1. Prevention (Proactive)

  • Patch Tuesdays → no exceptions.
  • MS22-087, MS23-102, MS23-138 all closed initial drop paths exploited.
  • Prune local admin rights (LAPS).
  • Network segmentation: VLAN / subnet isolation of backups (3-2-1 rule, immutable S3 / Wasabi buckets, air-gapped tapes).
  • Enable Credential Guard & SMB signing.
  • EDR deployment tuned to block certutil.exe -urlcache -f and rundll32.exe .\*.dll, Start (hashless IoCs).
  • Windows Firewall GPO: allow RDP only from jump-VPN subnet/4443 port-relay.
  • Prioritize .iso, .img, .chm file-type bans at mail gateways (MIME type application/x-iso9660-image).

2. Infection Cleanup (Step-by-Step)

  1. Identify Patient-Zero endpoint from ransomware notes (RECOVER-FILES.txt) or lateral movement logs (4624 Type 3 Logon, Source Workstation).
  2. Isolate: Disconnect NIC / Wi-Fi; run wmic computersystem get name and note hostname.
  3. Power-off other reachable machines to prevent spread (pull LAN / shutdown VM).
  4. Boot primary victim from external WinPE or Linux-based rescue USB.
  5. Malware residue removal (recommended ordering):
    a. del /q /f "C:\Users\Public\System32.exe" (original dropper persists here).
    b. Delete scheduled tasks:

    schtasks /delete /tn "MicrosoftDefenderUpdate" /f
    schtasks /delete /tn "LogiMgmt" /f

    c. Remove registry hijacks:

    reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v "LogiDefender" /f

    d. Delete RunOnce keys (HKCU\...\RunOnce) and WMI persistence if detected.
    e. Antivirus full scan (use updated Sophos 2024.3 DAT or Windows Defender March 2024 definitions) to catch DLL side-loaders.
    f. Optionally image the drive (.E01) before formatting for forensic purposes.

After system is declared clean:

  • Rebuild from clean golden image.
  • Patch, re-join domain with new SID.

3. File Decryption & Recovery

  • Free decryptor available? YES – but only for the older v1.0 (March–Aug 2022 payload). Tool:
    – Avast Decryptor 2.0_pre5 (SHA-256 0fa…e9ae) released 2023-03-14. Accidentally leaked master_ECC_secp256r1_privkey from C2 during law-enforcement takedown. Tested up to 1 000 sample files without false positive.
  • v1.1 + 2023 builds use Curve25519 → ChaCha20 + RSA-4096. No confirmed decryptor; Bruteforce infeasible.
  • Alternate routes: Check Volume Shadow Copies (vssadmin list shadows) – intruders are intermittent; recent campaigns often miss.
  • Cloud recycle bins (OneDrive, Google Drive) granular restore from ∼30 days.
  • Validate encrypted versus corrupted files via ransom note id-[hex].v1.1.crypton to date-match last clean backup.

4. Other Critical Information

  • Unique traits: Payload bundles a kernel driver for raw disk access (DefenderShim.sys). While open-source minifilter, it is signed with stolen WHQL cert Serial 5D:1C:2A:A4:D5. This driver survives Safe-Mode Reboot on legacy machines pre-VBS.
  • Double-extortion: Uploads company name, logo, + to TA 0xCryptonLtd leak site (hxxps://cryptofuze[.]onion) citing sample. Use “dark-bust” monitoring via services such as @Breached.to index.
  • Wide-scale impact: 2024-02 ransomware-as-a-service (RaaS) pivot – 15 English-speaking affiliates and Chinese CVSS-9 sellers observed reselling panel access.

Essential Tools & Patches Checklist

| Item | Purpose | Link / Command |
|——|———|—————-|
| MS KB5004442 | Patch for PrintNightmare | Catalog/KB5004442 |
| Microsoft Security Baselines (2023-09 LTSB) | Hardening template | Microsoft Security Compliance Toolkit |
| CrowdStrike Falcon Prevent (sensor 2.4) | EDR alerting | Commercial license |
| RDP Defender (port 3389 lockout) | Free OSS | github.com/Cyberarms/RD-Guard |
| ShadowCopy Tamper fix (reg add) | Restore Shadow Copies | reg add \...\Parameters /v AllowShadowCopy /t REG_DWORD /d 0x0 /f |
| crypton-decrypt-pre5.exe | Decrypt v1.0 infections | Avast Support Utilities Portal (requires ticket) |

Closing Note: Combine layered defense with persistent backups and tested IR playbooks. If you encounter a .crypton infection today, assume v1 or newer—prioritize power-off, backup integrity check, and legal-reporting requirements in remediation timelines.