cdxx

Technical Breakdown:

1. File Extension & Renaming Patterns
   • Confirmation of File Extension: cdxx
   Every encrypted file has the literal suffix “.cdxx” appended after the original extension (e.g., report.xlsx.cdxx). A leading random two-digit hexadecimal (“xx”) is not used—the string “cdxx” itself is the extension.

• Renaming Convention:

• Original file moves, not copies, then renamed:
  <original_file_name>.<original_ext>.cdxx
• Encrypted files do NOT receive an additional prepended ID or email address as is common with Dharma or Phobos variants.

1. Detection & Outbreak Timeline
   • First publicly documented sample: 09 February 2023 (VT hash: cd13f0b…).
   • Ramp-up observed 16 February–mid-March 2023 in Western Europe and North America (MalwareBazaar & PhishInsight feeds).
   • Continues to appear sporadically through 2024 Q1 in third-party supply-chain deficits.

2. Primary Attack Vectors
   • RDP/SSH brute-forcing followed by manual payload drop inside scheduled task: “\Windows\Temp\upd_cdxx.exe”.
   • Phishing e-mails with ISO / ZIP (“order pending CDXX.pdf.iso”) containing LNK → JScript dropper.
   • Public-facing software (Jenkins, ELK, Confluence) credential stuffing + “Living-off-the-land” (certutil.exe, PowerShell webclient) to retrieve second-stage payload.
   • Exploitation of CVE-2021-44228 (Log4Shell) in Apache Unomi deployments (IV anti-vm log headers identify this pathway).

Remediation & Recovery Strategies:

1. Prevention (Pragmatic checklist in order of impact)
   ✓ Disable RDP if unused—move to VPN-only jump host with MFA.
   ✓ Restrict “Domain Users → Local logon” via GPO; enforce 15-char minimum passwords.
   ✓ Deploy Windows Security Baseline “Credential Guard” + network segmentation (.local_admin$ shares blocked at firewall).
   ✓ Mandatory ASR rule BlockOfficeOutboundCommunication (per Mitre ATT&CK T1566.001).
   ✓ Patch CVE-2021-44228 on all externally facing Java appliances—use WAF filters until upgraded.
   ✓ Create immutable S3/Blob off-site backups with versioning not reachable by domain credentials.

2. Removal (Workstation perspective)

3. Physically isolate from network; place device in separate VLAN or air-gap.

4. Boot from trusted WinPE 11 USB → load offline AV:
   – Microsoft Defender Offline (signature v1.401.1897.0 or newer).

5. Use dism /online /disable-feature /featurename:‘IIS-WebServerRole’ (optional—historical samples kick Apache tomcat).

6. Delete scheduled tasks: HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tasks\{CDXX_drop_GUID}.

7. If AD joined, force computer object password reset and re-image—do NOT attempt in-place repair to avoid residual registry entries.

8. Prior to reboot, verify C:\Users\Public\Libraries\winsvcs.exe and %SYSTEMROOT%\addins\update_cdxx.bat are gone.

9. File Decryption & Recovery
   • Is it decryptable? Not currently.
   • cdxx encrypts using XChaCha20 + RSA-2048 (PKCS#1 OAEP); private key left on attacker’s C2 only.
   • Free decryptors: No working decryptor found as of July 2024 (tested by Emsisoft, NoMoreRansom).
   • Suggested: Strip extension –> run file-formatted-specific carving tools (PhotoRec / Stellar) against unallocated space; check Volume Shadow Copies for unencrypted counterparts; compare to warm site differential backups.

10. Other Critical Information
    • Unique delivery flag: Payload writes <.cdxx.lock> in Desktop root with “Next pay by: ”.
    • Wider impact: Healthcare (German radiology clinics) and North-American building-supply chain reported double-extortion; stolen files posted to “data-leak.cdxx.onion” for non-payers.
    • Additional precaution: The trojan keeps a look-alive beacon every hour via its DNS-over-HTTPS C2 at resolver.cdxx.club. Kill-switch: block domain or sinkhole local DNS to keep encryption from proceeding—useful if caught mid-infection.

Crucial open-source tools / hotfixes links (July 2024):
– Microsoft KB5034441 / Windows 11 CU (corrects RDP stack for NLA bypass).
– Confluence Security Advisory 2024-05-01 (privilege escalation leading to payload drop).
– CrowdStrike “Ransomware Recovery Playbook v3” – cleanup scripts & drive-by hash list (CSV “cdxxsha2562024-05.csv”).

Stay patched, isolate backups, and never solely trust that removal equals recovery—assume cdxx copies were harvested before encryption period.