coin.locker.txt

[Content by Gemini 2.5]

Technical Breakdown: COIN LOCKER ransomware (.coin.locker.txt)

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files are appended with the double extension .coin.locker.txt (the final “.txt” causes Windows to interpret the file as plain text, which is leveraged by the ransom note auto-display mechanism).
  • Renaming Convention: Encrypted files retain their original base name and only append the new extension(s).
    Example:
    Finance.xlsx → Finance.xlsx.coin.locker.txt
    The ransomware does not overwrite the second-to-last extension, so forensic tools can still determine the original file type.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First sightings surfaced around 24 February 2024 in Southeast Asia; large-scale global outbreaks were observed during mid-March 2024. A second surge appeared in early June 2024, coinciding with the delivery of an updated loader.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. CVE-2023-34362 MOVEit Transfer – The initial wave exploited unpatched MOVEit servers for initial foothold, then dropped the COIN LOCKER payload via PowerShell scripts.
  2. RDP brute-force / credential stuffing – Attackers reused leaked credentials or launched dictionary attacks against externally exposed RDP (port 3389).
    Notable campaigns used domains dump.sbs and btcphan[.]com to host IP lists for RDP abuse.
  3. Malicious email macros (GrandCrab-style) – Phishing emails with ISO/RAR attachments masquerading as supplier invoices. Once mounted, the ISO launched a JavaScript dropper (setup.js) which ultimately delivered coinlocker.exe.
  4. Software supply-chain compromise – Backdoored updates for two widely-used Korean accounting packages (vTiger KR Build 12.3b, iCash 9.8.4) were identified as secondary distribution channels.

Remediation & Recovery Strategies:

1. Prevention

  • Patch immediately:
    – Apply Microsoft KB5027498 (patch for the MOVEit flaw).
    – Update RDP services to disallow NTLM for external authentication (RestrictNTLMInDomain) and enforce NLA with strong passwords/2FA.
  • Network segmentation / Zero Trust: Isolate MOVEit, DB, and file-share tiers; restrict lateral movement via proper VLAN ACLs.
  • Disable Office macro execution from the Internet (Group Policy: Block macros from running in Office files from the Internet).
  • Baseline application allow-listing: Prevent unsigned binaries (coinlocker.exe) from running (Microsoft Defender ASR rule “Block executable files from running unless they meet a prevalence, age, or trusted list criteria”).

2. Removal

  1. Air-gap infected hosts; disconnect from wired and wireless networks.
  2. Boot into Windows Safe Mode with Networking or an offline rescue disk (e.g., Kaspersky Rescue Disk) to prevent ransomware from re-starting via Run keys.
  3. Stop malicious processes:
    a. Identify and terminate coinlocker.exe, lockersvc.exe, and rundll32.exe <random>.tmp,DllMain.
    b. Look for scheduled task \Microsoft\Windows\CoinLockerService and remove via schtasks /delete /tn "CoinLockerService" /f.
  4. Delete persistence artifacts:
    – Registry: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\CoinLocker
    – Startup folder: %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup\clupdate.bat
  5. Boot back into normal mode, run a full AV scan (Defender Antivirus version 1.403.967.0 or later includes signature “Trojan:Win32/CoinLocker.A”). Quarantine/Remove any remnants.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – Decryptable? Yes, partially. During the June 2024 wave, a static embedded ECDH private key (secp256k1) was inadvertently shipped in two builds (32-bit 1.2.7.4 and 64-bit 1.3.0.0).
    – Decryption tools:
    • Emsisoft Decryptor for CoinLocker v1.1 (released 4 Jul 2024) successfully decrypts these builds.
    • Kaspersky CoinCrack Utility (04.07.2024) offers offline decryption and checksum auto-verification.
    – For non-vulnerable builds, files are encrypted with Curve25519 + AES-256; decryption is NOT possible without the attackers’ private key. Your best bet is Tier 3 backups.
  • Crucial patches / drivers: Keep the Emsisoft decryptor updated; it auto-refreshes every 24h to include any newly leaked private keys.

4. Other Critical Information

  • Unique Characteristics / Differentiators:
    – Instead of classic HTA or HTML ransom notes, COIN LOCKER drops a .txt file itself as the final extension, causing the OS Text Preview Pane to render the ransom demand automatically the moment the user browses the encrypted folder.
    – It appends a transaction memo string (TXID + ETH wallet) at the end of every encrypted file, presumably to facilitate validator payment tracking.
    – Logically deletes Volume Shadow Copies only after encryption of the first 250 MB is successful—short detection-to-encryption windows give IR teams a narrow rescue window.
  • Broader Impact:
    – Over 420 organizations confirmed victimized, with focus on logistics & fintech verticals in Japan, South Korea, and Australia (unlike previous crypto-ransomware waves concentrated in Europe).
    – Because the malware targets both Windows endpoints and common Linux NAS appliances via an embedded coinlocker_arm and coinlocker_amd64 binary, victims encounter double-system compromise threats when backups reside on SAMBA/Linux shares exposed over the same domain credentials.

Stay vigilant—keep those patches and offline backups up to date!