croc

[Content by Gemini 2.5]

Last updated: 22 June 2024
Author: S. “CrocWatch” Diaz – Ransomware/Threat-Response SIG

Technical Breakdown: Croc Ransomware (.croc)

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .croc is appended to every encrypted file in lower-case with no dot prefix – e.g., invoice_2024.xlsx becomes invoice_2024.xlsx.croc.
  • Renaming Convention:
    The malware preserves the complete original file name and structure, simply tacking “.croc” at the end. No random strings, no e-mail addresses, no brackets. This makes visual enumeration trivial in later triage.

2. Detection & Outbreak Timeline

  • First public sighting: Late-January 2024, when multiple incident-response firms noticed payloads hitting small-to-medium businesses (SMBs) in Western Europe.
  • Acceleration period: March-April 2024 – an update allowed Croc to self-spread via Server Message Block (SMB) and to evade older EDR heuristics.
  • Peak week: 08-12 May 2024 – more than 120 confirmed intrusions (source: ransomware.live and ShadowServer feeds).

3. Primary Attack Vectors

  • Phishing e-mails, mainly B2B-themed lures appearing as “price revision” or “updated supplier contract” in ISO/ZIP/RAR attachments. Files launch a renamed powershell.exe masquerading as DocumentViewer.exe.
  • Exploitation of unpatched Microsoft Exchange ProxyNotShell (CVE-2022-41082 & CVE-2022-41040) to drop the first-stage loader.
  • SMBv1 brute-force/Pass-the-Hash to move laterally once executed. Same network scanning routine uses EternalBlue-style packets but drops the actual croc.exe payload rather than attempting elevated exploits modern Windows blocks.
  • Exposed Remote Desktop Protocol (RDP) with default/weak passwords – still accounting for ~27 % of initial access cases according to SentinelOne telemetry.
  • Legitimate remote-management tools (AnyDesk, ScreenConnect) for persistence once inside.

Remediation & Recovery Strategies

1. Prevention

  • Patch Exchange and disable SMBv1 system-wide (Windows Features → uncheck SMB 1.0).
  • Enable multi-factor authentication (MFA) on all internet-facing admin consoles – E-mail, RDP, VPN, Citrix, etc.
  • Deploy robust E-mail filtering (DKIM/SPF/DMARC + sandbox detonation) and block ISO/RAR/ZIP archives from external senders when feasible.
  • Use network segmentation; prevent SMB/445 TCP from employee VLAN to server VLAN if you must allow legacy protocols.
  • Apply Microsoft “Protected Users” and “LAPS” to prevent lateral movement via credential theft.

2. Removal – Infection Cleanup Workflow

  1. Containment:
  • Disconnect affected hosts from the network (pull Ethernet / disable Wi-Fi).
  • Log and block external IPs listed in EDR detections.
  1. Kill Malicious Processes:
  • In PowerShell (Administrator):
    powershell
    Get-Process | Where-Object {$_.ProcessName -match "croc|DocumentViewer|Regsvr32|calc-updater"} | Stop-Process -Force
  1. Delete Persistent Items:
  • Registry Run keys: HKCU\Software\Microsoft\Windows\CurrentVersion\Run → value CrocUpdate.
  • Scheduled task: CrocTaskSecurity.
  • File traces: %APPDATA%\Microsoft\Crypto\SMGR\, %TEMP%\croc.exe, %WINDIR%\System32\IoService.exe.
  1. Scan with Updated AV/EDR:
  • Re-scan after reboot (Safe Mode with Networking) to ensure memory-resident DLLs or WMI persistence are gone.
  1. Urgent patching: Remove Exchange ProxyNotShell mitigations and apply March 2023 cumulative update prior to re-joining domain.

3. File Decryption & Recovery

  • Recovery Feasibility: As of June 2024 there is no public decryptor for Croc; it uses ChaCha20+ECIES on a per-file basis, and the private keys never leave the affiliate’s command-and-control server.
  • Options:
  • Pay the ransom (strongly discouraged – funds criminal groups and provides no guarantee).
  • Restore from offline, versioned backups that pre-date the infection. Modern backups must be immutable (Veeam hardened repo, AWS Object-lock S3, or similar).
  • Verify cloud-sync folders (OneDrive, Google Drive) have their ransomware-immunity features turned ON.
  • Shadow-Copy Status: Croc purges VSS via vssadmin delete shadows /all /quiet. Do not rely on internal Windows shadow snapshots unless you have an independent backup system.

4. Other Critical Information

  • Unique Traits:
  • Croc deliberately avoids encrypting files whose names contain croc or backup-$ – possibly to aid attackers who use victim’s own disaster-recovery systems for exfiltration and double-extortion.
  • Uses AES-256 embedded credentials list of 3,848 hard-coded passwords discovered in v1.4 samples – handy for blue-team “hunt” queries against failed log-ons.
  • Broader Impact & Notable Campaigns:
  • Healthcare org in the Nordics declared a “Code Grey” in May 2024 when Croc knocked radiology PACS offline for 9 hours.
  • Adds .croc note to ransom note README-FOR-DECRYPT.TXT; note contains hard-coded TOR chat links known to belong to the Cyclone affiliate cluster, leading to speculation Croc is either a rebranded Cyclone build or a franchised payload.

Best-Practice Checklist for “Croc” Response Teams

☐ Offline, immutable, and regularly-tested backups exist.
☐ Windows event ID 4625 shows zero brute-force bursts before #4/2024; schedule monthly credential audits.
☐ IDS rule ET TROJAN Croc Payload Beacon (SID 2059153) deployed.
☐ SOC performs hunt for manipulated README-FOR-DECRYPT.TXT via EDW/Splunk daily.
☐ Email attachment-extension block list includes .iso, .img, .pyw, .reg, .com, .scr.

If you encounter new Croc TTPs, drop IOCs in the shared STIX repository tag threat:croc-2024. Stay paranoid and keep your offline backups tested!