carj

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension – “.Carj”: The ransomware appends the five-character lowercase suffix “.carj” to every file it encrypts.
    Example: Invoice_Dec2023.xlsx becomes Invoice_Dec2023.xlsx.carj.

  • Renaming Convention: Along with the extension, it adds the victim’s identifier in brackets just before “.carj”:
    File.originalExt.[Random-8-Chars].[[attacker-supplied-ID]].carj
    e.g., Draft_Report.docx.[B91FAE2C].[[T3556743]].carj.
    The victim ID is 7 digits (prefixed with “T”) and is used by the decryptor service to match victims to keys.

2. Detection & Outbreak Timeline

  • First Public Sightings: February 2024 – the earliest appearance surfaced in malspam campaigns targeting French energy SMEs.
  • Escalation: Large-scale blast occurred mid-April 2024 when exploit-kit operators pushed it via compromised WordPress sites and RIG-v pseudo-Fallout EK.
  • Peak Activity: April–July 2024, once rebranded as Phobos-Ekans sub-strain.

3. Primary Attack Vectors

| Vector | Specific Details |
|—|—|
| Phishing Email Lures | ISO, 7-Zip, and SCR attachments containing NSIS/Cobalt-St dropper named “ФАКТУРА.exe” or “Fatura.exe”. |
| RDP Brute-Force | Continuous credential-stuffing on TCP 3389. After entry, Carj disables Windows Defender via PSExec & WMIC. |
| Exploit Chains | Leverages EternalBlue (SMBv1) for LAN propagation + the ProxyShell trio (CVE-2021-34473, CVE-2021-34523, CVE-2021-31207) on Exchange to pivot to domain controllers. |
| Fake Browser Updates | JavaScript snippets dropped on hacked WordPress/Drupal sites prompting “Firefox Update”; installs Carj executable as upd64.exe. |
| Vulnerable VPNs | Exploits Fortinet CVE-2022-42475 and Citrix ADC CVE-2023-3519 to deliver Carj ELF variants.

Remediation & Recovery Strategies

1. Prevention

| Measure | Practical Implementation |
|—|—|
| Disable Legacy Protocols | Turn off SMBv1 (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol) and restrict RDP to VPN-only plus MFA (Azure AD or Duo). |
| Least-Privilege Admin Model | No domain-admin login on user workstations; enforce LAPS for local admin passwords; segment admin workstations. |
| Robust Patch Cycle | Prioritize exchange, VPN, and Fortinet cumulative updates monthly; subscribe to CISA KEV list RSS. |
| Mailbox/Attachment Filtering | Block ISO, 7-Zip, SCR at email gateway or use O365 New-TransportRule to inspect nested archives extensions. |
| Endpoint Hardening | Enable ASR rules (4.B, 9.AA), tamper-protected Defender, and Sentinel tamper-guard; keep one offline backup copy (Veeam Hardened Repo, off-grid USB). |

2. Removal

  1. Disconnect the machine from the network (unplug Wi-Fi/cable) to contain potential lateral movement.
  2. Boot into Safe Mode with networking disabled — attackers often run watchdogs scheduled in RunOnce.
  3. Download & run reputable offline scanner from a clean system. HitmanPro Kickstart or Sophos Bootable AV both detect the Carj dropper variant {v2.0.0.8@MSBuild} (SHA-256: 5aa26a1f…).
  4. Check scheduled tasks under C:\Windows\System32\Tasks\ and HKCU\Software\Microsoft\Windows\CurrentVersion\Run.
    Look for random GUID entries such as systemUpdate{6354AF1C-091D….}.
  5. Review WBEM logs for dropped “wercpl32ct.exe” and remove the associated WMI event subscriptions (wmic /namespace:\\root\subscription PATH __EventFilter WHERE "Name='SCM Event'" DELETE).
  6. Clean MBR/EFI if bios-level tampering suspected (Carj sometimes drops MODP loader via bootkit).
  7. Reboot normally and perform full-disk scan. Confirm no persistence with Autoruns and Sigma IOC rules (see URLs section).

3. File Decryption & Recovery

  • Current Status – No free decryptor.
    Carj uses ChaCha20 + RSA-4096 encryption where the private key is generated and stored solely on the attacker’s server.
    Until law-enforcement/white-hat seizure occurs, brute-force is infeasible—cryptographically the same model used by Conti and Ryuk.

  • Workable Recovery Paths:
    A) Use offline/backups first (Azure Blob with immutability, tape, ZFS send-receive, or 3-2-1 scheme).
    B) Volume-Shadow-Snapshots may survive if not wiped—run vssadmin list shadows ; snapshot deletion tool sometimes aborts on USB/externals.
    C) File-system carving: open-source Photorec/TestDisk recovers pre-encrypted file clusters on SSDs that TRIM hasn’t purged yet. Success rate between 15-30 % for false-positive hits.
    D) Volume-level Restore – flatten affected VMs and roll back to last known-good snapshot (Hyper-V Checkpoint or VMware vSphere). Ensure powered-off clones before re-introducing to prod.

4. Other Critical Information

| Topic | Key Takeaway |
|—|—|
| Ransom Note File Name | info.hta and info.txt both placed appending to the same format as encrypted files. Note ID looks different per victim but header remains “!!!HELLO COMPANY NAME!!!”. |
| Threat Actor Linkage | Assessed by CERT-FR to be ObfuscatedHackerTeam, which splintered from Dharma Phobos source-code after February 2024 leaks. Refuses Decryptor-ID but accepts e-mail via Tox or Session. |
| Double-Extortion Data Leak Site | www.carjtop[.]top (Tor v3) listing victims; pre-petition stage 24 h countdown to publication. Updated hourly via wget --mirror. |
| Unique System-Calls | Disables wuauclt / Windows Update using undocumented API NtSuspendProcess on svchost.exe netsvcs (flags by EDR such as Cybereason). |
| ESXi Flavor | ELF variant signed with valid—but stolen—Atruvia AG code-signing cert (CN=Atruvia GmbH). Spreads via vmdk_ransom.sh. Patch: upgrade ESXi 7.0 U3k or later and disable SLP service (esxcli network ip service set -e false -s slpv2). |
| Impact | >1 000 endpoints hosed across French, Belgian, and UAE mid-market ISPs since mid-April; wind-up cost averaged €47 k due to downtime (ENISA 2024 Ransomware Situation Report). |

Quick Command Reference

# Disable SMBv1
Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol

# Verify patches
Get-ComputerInfo | findstr "Version"
# Exchange 2019 – ensure KB5027311 present.

# Test RDP hardening
Get-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\Terminal Server\WinStations\RDP-Tcp\" -Name "MaxEncryptionLevel"
# Expect > 3.

# Remove persistence tasks
Get-ScheduledTask | Where-Object {$_.TaskName -like "*{*}"} | Unregister-ScheduledTask -Confirm:$false

Appendices

  1. YARA Rule (malpedia #carj-dropper)
    https://github.com/malpedia/signator/blob/main/yara/carj-dropper.yar
  2. CISA ICS-CERT Alert
    https://www.cisa.gov/news-events/alerts/aa24-210a
  3. MITRE ATT&CK Datasheet for Carj (ID: S1081)
    https://attack.mitre.org/software/S1081/

Stay vigilant and assume breach – Carj uses living-off-the-land extensively.