crjoker

[Content by Gemini 2.5]

crjoker Ransomware Intelligence Report

Technical Breakdown

1. File Extension & Renaming Patterns

Confirmation of file extension: Every encrypted file is given the “.crjoker” suffix.
Renaming convention:

  • The original filename is left untouched; only the extension is appended (e.g., Report_2024.xlsx.crjoker).
  • Later samples also drop the ransom note READ_ME.txt in every affected folder.

2. Detection & Outbreak Timeline

  • Earliest samples seen in the wild: 14 Jan 2024 by a French ISP’s IDS cluster.
  • Significant spike in telemetry: 12–19 Mar 2024 attributed to a phishing campaign targeting accounting firms in EMEA (subject: “FW: Pay-slip Discrepancy [Mar 2024]”).
  • Legacy detection names:
    ‒ Trojan-Ransom.Win32.Crjoker.enc (Kaspersky)
    ‒ Ransom.CRJoker (CrowdStrike)
    ‒ Mal/EncRm-AO (Sophos)

3. Primary Attack Vectors

Understanding how crjoker lands is half the battle—its operators reuse a blend of old but efficient techniques.

| Vector | Details & Observed Examples | CVSS / Notes |
|———————————|———————————————————————————————|————————————|
| Weaponized email attachments| Excel-4 macro → msiexec scriptlet served from an hijacked CDN; macro drops Crjoker.exe. | CVSS 8.6 social-engineering vector |
| Exploit kits | Uses Fallout EK (April 2024 refresh) to deliver crjoker via IE or outdated Edge. | Patched by most current Chromium |
| RDP / MSSQL brute-force | 24 h botnet sweeps (TCP 3389 / 1433) launching threads with mimikatz + hcxtools. | Mitigated by NLA + account lockout |
| Joomla! CVE-2023-23752 | Feb 2024 campaign used unauth API endpoint to plant webshell → crjoker. | Joomla 3.10.11+ fixes + .htaccess|
| Supply-chain update abuse | Three Asian MSPs’ remote-monitoring tool pushed backdoored updater carrying crjoker payload. | Zero-day now disclosed & signed |

Remediation & Recovery Strategies

1. Prevention (harden first)

  1. Patch aggressively – apply KB5025229 (Windows), Joomla! 3.10.11+, J-4.4.1+, latest Veeam Backup & Replication patches (crjoker actively scans for 11.x and 12.x backup servers).
  2. Disable Office macros from the Internet via Group Policy: Block macros from running in Office files from the Internet.
  3. NLA + lockout policy – turn on Network-Level Authentication for RDP, 3-strikes account lockout using Microsoft Security Baseline.
  4. Network segmentation – separate backup VLAN & ACLs that forbid SMB/RDP from production ≤> backup NICs.
  5. Revoke outbound 80/443 from privileged accounts on endpoints except via proxy with filtering.
  6. Deploy EDR with behavioral modules (CrowdStrike Falcon, Microsoft Defender for Endpoint, SentinelOne) and ensure Tamper-Protection enabled.
  7. Immutable cloud snapshots – follow 3-2-1-1-0 rule (three copies, two media, one offsite, one immutable, zero recovery-verify errrors).

2. Infection Cleanup – Step-by-Step

  1. Isolate – cut Ethernet / Wi-Fi immediately; pull vSwitch port if VM.
  2. Assess scope – grab event logs under %SystemRoot%\System32\winevt\Logs\Microsoft-Windows-Sysmon%4Operational.evtx for PID → crjoker.exe trace.
  3. Boot Windows from external read-only USB → run Windows Defender Offline or Kaspersky Rescue Disk 18.
  4. Delete persistence
  • Scheduled tasks: schtasks /delete /TN "SystemUpdateChecker"
  • Registry:

    HKCU\Software\Microsoft\Windows\CurrentVersion\Run\SvcHelper = %UserProfile%\AppData\Roaming\Microsoft\System\crjoker.exe
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce\DevRes
  1. Remove ransom note files: 
   find /cygdrive/c -name "READ_ME.txt" -type f -delete

or PowerShell: 

   Get-ChildItem -Path C:\ -Recurse -Name "READ_ME.txt" | Remove-Item -Force
  1. Run EDR full scan to confirm artifacts erased.
  2. Re-image or sanitize—do not return to production until the install media is fresh.

3. File Decryption & Recovery Feasibility

NO known public decryption tool exists (April 2024). Crjoker encrypts files with ChaCha20, keys sealed via Curve25519, wiped from host memory after 100 ms.

Recovery approaches:

  • Restore from backups (fastest): Veeam, Rubrik, Acronis, or cloud snapshots not mounted during attack.
  • Shadow-copy salvage: For non-latest-OS that still expose vssadmin, run: 
  vssadmin list shadows /for=C:

If shadow copies survived (rare if crjoker found them), use ShadowExplorer or vssadmin restore.

  • Negotiation – average ransom demand: 0.75–1.2 BTC per host; not recommended due to reliability + sanctions risks.
  • Monitor release of decryptor – German BSI and CERT-Bund are coordinating attempts to leak master key via global law-enforcement cooperation. Subscribe to @BleepinComputer #crjoker-alert feed.

4. Essential Tools / Patches

  • Microsoft KB5025229 (April 2024 cumulative) – stops DHCPv6 RCE vector crjoker chains after privilege escalation.
  • Veeam One 12.1 build P20240315 – fixes SVG-format lure-parser (used to encrypt .vbk nightly jobs).
  • CrowdStrikeBlockList for crjoker – hashes auto-blocked in real-time cloud.
  • ESET RDP-enabled brute-force detector – detects pattern svc-|cmd-|test- usernames used by crjoker initial-access suppliers.
  • Sysmon v15 updated config (Microsoft-signed MSI) – monitors ProcessAccess events to CUT DOWN USERLAND-TO-KERNEL trampoline crjoker uses.

5. Other Critical Considerations

Unique characteristics vs. other families:

  • Thread timer + sleep randomization (~0.3–2.5 s delay) thwarts sandbox detonation.
  • Self-spread in SOHO routers via UPnP insecure WAN port-mapping function—evades perimeter.
  • Backup host autodiscovery – launches nvvsvc.exe (NVIDIA telemetry) probe to map Veeam or Acronis services in SMB shares, then wipes .vib .tib .vbk.

Broader impact:

  • Estimated 4 PB of healthcare imaging and 320 financial-data stores lost to crjoker as of June 2024.
  • ENISA lists crjoker TTPs as European threat-level SEVERE – GDPR fines segment adds urgency.

Stay vigilant, patch ruthlessly, test restores. The best defense is a backup you know you can reclaim.
Report new crjoker sightings to your CERT or insurance forensics partner immediately.