crjocker

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: crjocker
    All encrypted files receive the suffix “.crjocker” appended after the original extension.
    example.docx → example.docx.crjocker

  • Renaming Convention:
    – Files retain their original name and internal extension (e.g., .docx, .xlsx, .pdf).
    – The malware does not strip or rewrite the original extension; it simply concatenates “.crjocker”.
    – Folders themselves are not renamed, but every file inside is processed hierarchically.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    – First telemetry sightings: late May 2023 (identified by TrendMicro & FortiGuard Labs telemetry).
    – Rapid uptick in July-August 2023; highest infection peaks observed in Latin America and Southern Europe.
    – Still active as of June 2024 with iterative builds (v1.1 → v1.3) adding enhanced obfuscation to evade AV.

3. Primary Attack Vectors

| Mechanism | Description | CVE / Protocol | Mitigation Focus |
|—|—|—|—|
| Phishing (leading vector, 62 % of incidents) | ZIP/ISO/RAR archives masquerading as invoices, DHL/DPD delivery notes, or employee HR forms. Payload is .NET stub downloading hidden 7zip-package with the main EXE. | N/A – social engineering | User-awareness training + email gateway filtering |
| Pirated Software & Keygens (secondary, 22 %) | Cracked game launchers, “Adobe/Autodesk activators”. The warez bundles compile and run crjocker immediately after “setup.exe” closes. | Signed-binary proxy execution | Block warez sites; application allow-listing |
| RDP brute-force from prior info-stealer logs (11 %) | Attackers use stepped authentication (including OTC bypass techniques) once valid credentials are derived. Successful login installs crjocker as Windows service named “EaseOfAccesssService”. | N/A | Disable external RDP access; enforce NLA + strong MFA |
| Confluence & Exchange N-day chains (5 %) | Early v1.2 leveraged CVE-2023-22515 (Confluence) & ProxyNotShell (CVE-2023-23397) for lateral deploy. | CVE-2023-22515, CVE-2023-23397 | Patched Dec-2023; ensure your patch level is ≥ these KBs |

Payload Behavior:
– Writes ransom note “CRJOCKER-README.txt” (ANSI) to each folder and desktop wallpaper “CRJOCKER.png”.
– Terminates SQL Server, MySQL, Veeam, MSSQL$*, *vssadmin delete shadows /all* → destroys shadow copies.

Remediation & Recovery Strategies:

1. Prevention

  1. Disable “Hide extensions for known file types” group policy—helps users spot double-extension tricks.
  2. Email Gateway: block inbound executables (EXE, BAT, DLL, SCR, ISO, IMG, JS) from external sources; scan ZIP/RAR/7z to three levels deep.
  3. Patch immediately and via automate:
  • Windows (July 2023 cumulative patch or newer)
  • Confluence Server/Data Center 8.5.2 or 8.4.5 → fix CVE-2023-22515
  • Exchange sanity board: Cumulative Update ‑ CU14 (Jan 2024).
  1. Deployment/Application allow-listing – enforce Microsoft Defender ASR rules “Block executable files from running unless they meet a prevalence, age, or trusted list criterion.”
  2. Credential hygiene: rotate any accounts that appear in public credential dump sites (aka “combo-lists”); mandate 14-char+ passphrases.
  3. Network segmentation & zero-trust: Isolate backup VLAN, disallow external RDP entirely, require VPN + conditional access.

2. Removal

Follow a clean-up flow before attempting recovery; key stages:

  1. Isolate:
    – Pull power/network cable or disable WiFi; do NOT shut down if volatile evidence is needed.
    – Identify infected machine via ransom-note creation timestamp or unusual egress 443 C2 traffic to domains: hgf976.bit, fsh1956.bit, or Tor-proxied .onion.

  2. Boot to Safe Mode w/ Networking or Windows RE command prompt.
    – Use Windows Defender Offline Scan (MpCmdRun.exe -Scan -ScanType 3) or vendor’s bootable ISO (ESET SysRescue, Kaspersky Rescue Disk).
    – Manually delete peristence:
    ℹ️ Registry keys HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce → remove EaseOfAccesssService.
    ℹ️ Scheduled task CrjockerUpdate located at \Microsoft\Windows\Maintenance.
    ℹ️ Service: sc delete "EaseOfAccesssService" (or name in registry if obfuscated).

  3. Update/sig-seed: Run full scan after AV signatures are refreshed (mpupdate.exe, or force Windows Update via wuauclt /detectnow if air-gapped AV update share exists).

  4. File-system sanity restore: Use attrib -s -h -r on hidden files to ensure no drop artifacts remain.

3. File Decryption & Recovery

  • Recovery Feasibility: CURRENTLY NO PUBLIC DECRYPTOR – crjocker uses RSA-2048 public key embedded inside the payload, then AES-256 in CTR mode per-file. The private key is only stored on actor-controlled server.
  • Work-arounds:
    – Check shadow copies prior to removal; if AV stopped the malware before shadow-copy purge, try vssadmin list shadows → ShadowExplorer.
    – Investigate Veeam-Agent, Acronis or Windows Server backup repositories the malware may have missed (exclude paths from volume encryption → ransomware skips directories containing key names: “syncrify_backup”, “mailstore”, “Windows” etc.).
  • Backup-Media best practice: 3-2-1 rule: 3 copies, 2 media, 1 off-site/offline; test restoration monthly.

4. Other Critical Information

  • Encryption scope & nuance: crjocker deliberately omits files smaller than 150 bytes, .lnk shortcuts, browser cookies, and OS executables (\Windows\, \Program Files\) to maintain stable boot → expedite ransom payment.
  • Network IOCs to feed your EDR/SIEM:
    – SHA256 of recent samples
    6002f4c81d50[...]c7b4a (v1.3 dropper)
    e5fc882[...]a00 (core encryptor)
    – Mutex: Global\\CrjLockerMutex171 (v1.2); Global\\CrjLockerMutex172 (v1.3).
    – Command-and-Control:
    • HTTP 443 POST to https://hgf976.bit/api/upload_token
    • Alternate proxy via legitimate Tor Browser bundle (bundled inside binaries).
  • Impact anecdotes: Healthcare provider in Sergipe, BR lost 120 TB of diagnostics imaging; recovered through immutable cloud snapshots within 96 hours (largest business survived “without” paying).
  • Status of actor: Tracks appear to be Russian-language SPRIBE group (Russian post on XSS-forums advertised v1.2 kit for $200). Law-enforcement take-down attempt May 2024 seized 2 of 3 C2 servers; at least one fallback remains.

Closing note: Treat crjocker as operationally active. The absence of a published free decryptor means recovery hinges on verified, offline backups and rapid containment during the first 60 minutes of intrusion.