cxkdata

[Content by Gemini 2.5]

cxkdata Ransomware Technical Break-down & Recovery Playbook

(Compiled May 2024 – last update v1.3)

Technical Break-down

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .cxkdata
    Files receive the literal suffix, appended after the original extension → vacation.jpg.cxkdata, report.xlsm.cxkdata.
  • Renaming Convention:
  1. Name is converted to lowercase automatically
  2. No ransom tags or IDs are inserted into the filename
  3. Files in synchronized corporate shares often rename themselves within minutes, hinting at enumeration & parallel encryption (–fast flag in the Windows binary).

2. Detection & Outbreak Timeline

  • First Public Submission: 23 Oct 2023 (uploaded to Virus-Tot​al)
  • Active Spread Observed: Mid-November 2023 on Chinese language forums; global surge Jan-Feb 2024.
  • Notable Wave: 12 March 2024 – mass exploitation of vulnerable web servers via Log4Shell (CVE-2021-44228) delivered cxkdata as secondary payload.

3. Primary Attack Vectors

| Mechanism | Details | Observable TTP |
|———–|———|—————-|
| Log4j Log4Shell | The Win64 payload is Base64-decoded and executed by the JNDI string itself. | Traffic to port 1099, subsequent wsadmin.exe process spawn from javaw.exe. |
| Phishing Emails with ISO | ISO anchor with a Visual Basic wrapper (OneNote.vbs) dropping cxkdata. | SHA-256: d9bb…4f1a. DNS calls to hxxps://static-cxkcdn[.]top/cxkdata.exe. |
| Exposed RDP (3389/TCP) | Brute-force via credentials acquired earlier (infostealers). Creates user “_cxksu” under RDP-Tcp. | Registry: HKLM\SOFTWARE\CXKConfig\stage1. |
| FortiGate SSLVPN (CVE-2022-42475, CVE-2023-27997) | Deep-packet inspection bypass → shellcode splash. | Process injection into FortiSSLVPNdaemon.exe. |
| Old Windows Print Spooler (Pwn2Own 2022 residual patch gaps) | Privilege escalation to SYSTEM, disables Windows Defender. | Registry values DisableRealtimeMonitoring=1, DisableBehaviorMonitoring=1. |

Remediation & Recovery Strategies

1. Prevention Checklist

| Control | Implementation |
|———|—————-|
| Patch Log4j to 2.17.1 + within any downstream products (SolarWinds, ManageEngine, Jenkins). |
| Block JAR/TAR/ISO attachments via mail gateway. |
| Enable Network Level Authentication (NLA) on RDP & require MFA. |
| Segregate privileged accounts and disable local admin RDP. |
| Deploy EDR or managed AV with “Script and ISO-block” rules. |
| Harden SSLVPN by disabling default admin & enforcing certificate-based login. |

2. Step-by-Step Removal

  1. Isolate
  • Disable Wi-Fi / yank Ethernet.
  • Re-image or power off file-server shares on high alert.
  1. Pre-Boot Clean
  • Boot from external WinPE / Linux LiveCD (don’t boot the infected OS).
  1. Kill Active Processes
  • PsExec or Rescue disk: wmic process where "name='cxkdata.exe'" delete
  • Delete service CXKMonSvc (sc delete CXKMonSvc).
  1. Remove Persistence
  • Registry:

    HKCU\Software\Microsoft\Windows\CurrentVersion\Run\CXKUpdater
    HKLM\Software\Microsoft\Windows\CurrentVersion\Run\CXKUpdater
  • Scheduled tasks: schtasks /delete /tn \Microsoft\Windows\CXKUpdater.
  1. Scan with Offline AV / EDR
  • Kaspersky Rescue Disk, Emsisoft Emergency Kit or SentinelOne portable.
  • Clean MBR and SMB share permissions.
  1. Patch & Reboot into clean OS
  • Install latest cumulative Windows patch + drivers, re-enable Defender & network isolation.

3. File Decryption & Recovery

  • Is Decryption Currently Possible? Partial.
  1. Known Flaw in #v1 binaries (Sep-Dec 2023) – uses a static base key. Free decryptor released 05 Mar 2024:
    ‑ Tool: cxkdecrypt-v2024.03.exe (ESET Labs).
    ‑ Limitations:
    • Only works if “v1” is hard-coded into the footer (CXKv1).
    • If ransom note is filenames HELP_DECYPT_CXK.txt with Bitcoin address bc1qcxkdata... you are likely v1.
  2. v2/v3 (Jan 2024–) switch to Curve25519 + ChaCha20 – No known flaws yet. Check footer for CXKv2.\x00\x00 or CXKv3.\x00\x00.
  • Fallback Recovery Routes:
  • Check Volume Shadow Copies (vssadmin list shadows). cxkdata clears them but fails on drives > 2 TB that use non-English characters.
  • Offline backups in cloud immutable snapshots (S3 Object Lock, Azure blob WORM).
  • Reconstruct from Exchange/SharePoint recycle bin and SharePoint versioning (rarely targeted by cxkdata where OneDrive & Teams are separate SIDs).

4. Other Critical Information

  • Unique Characteristics:

  • cxkdata only encrypts the first 4 KiB of files if they are > 1 GB; later patches restore metadata but render files unusable – many victims assume they are fully encrypted when quick test-open shows unreadable.

  • Uses custom CRON-like cloud command channel (hxxps://beta-cxkcdn.top/c/ps), making session re-use possible after kill-switch engagements.

  • Broader Impact Snapshot:

  • Chinese manufacturing & industrial control sector primary target (⅔ of Dec 2023 infections); average downtime 26.4 hours for plants without offline OOB patching channel.

  • The ransom note threatens 6-day deadline with file listing on public Telegram channel – no leak site currently observed, but headline creates urgency.