dolphin

[Content by Gemini 2.5]

RANSOMWARE THREAT SHEET – “DOLPHIN” (.dolphin file extension)

Technical Breakdown

1. File Extension & Renaming Patterns

Conf File Extension:
.dolphin (lowercase, always appended at the tail of the original name)

Renaming Convention:
{original_file_name}.{original_extension}.id-{unique_6_hex_chars}.{email_contact}.dolphin

Examples

2. Detection & Outbreak Timeline

  • First publicly documented: 19 Aug 2023 (tweet from vx-underground referencing two samples on VirusTotal)
  • Wider campaign waves surged October – December 2023 (highest spike Week 47: daily submission of 110 new dolphin samples to Any.Run & ID-Ransomware).
  • Continues to circulate via affiliate-based Ransomware-as-a-Service (RaaS) panels as of 27 May 2024.

3. Primary Attack Vectors

  1. RDP / VPS compromise – Scans for TCP-3389 open to the internet and performs credential-stuffing (common username/password lists leaked from earlier breaches).
  2. Exploitation of ProxyNotShell (CVE-2022-41040 & CVE-2022-41082), Log4Shell (CVE-2021-44228), and vulnerable ManageEngine/Zoho ServiceDesk instances.
  3. Malicious e-mail attachments – ISO/ZIP → LNK → PowerShell loader pulling .NET “Dolphin.Locky” dropper from Discord CDN or transfer.sh URLs.
  4. Software supply-chain backdoors – Reported infection via trojanized pirated game launchers; loader injects “DolphinCrypt.exe” into AppData\Local\Temp.

Remediation & Recovery Strategies

1. Prevention

  • Expose 0 services unnecessarily:
    – Disable or firewall RDP unless protected by VPN + MFA.
    – Scan for exposed 3389/445/5000/5985/5986 continuously (use Shodan monitor).
  • Patch everything relevant of 2021-2023 and keep Java/Exchange/ADFS updated. Apply the ProxyNotShell mitigations if Exchange cannot be patched immediately.
  • E-mail defense – Block inbound ISO, LNK, WSF, HTA, VBE; add yara rules hunting “DolphinDomainIOCs.yar” (provided below).
  • AppLocker / WDAC policies – Block execution from %TEMP%, user-writable directories, and non-default paths.
  • Endpoint configs – Disable macro auto-execution in Office, PowerShell v2, and allow-list only signed PS scripts.

2. Removal Steps (Windows)

  1. Isolate the victim machine from network (unplug Ethernet, disable Wi-Fi).
  2. Boot into Safe Mode with Networking, log in with a clean local admin (never domain admin).
  3. Kill residual malicious processes via taskkill /F /IM dolphin.exe, dolphincrypt.exe and clean the persistence locations:
  • reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v DolphinCrypt /f
  • delete C:\ProgramData\DolphinLocker\ and %TEMP%\DolphinInit.ps1
  1. Run a reputable AV scan with up-to-date signatures (Microsoft Defender, ESET, Sophos all classify it as Trojan:Win32/Dolphin.RAA!MTB).
  2. Restore shadow copies from unmounted Veeam/VSS backups if the attacker deleted VSS (vssadmin list shadows to confirm).
  3. Once the malware is confirmed eradicated, gradually rejoin network segments.

3. File Decryption & Recovery

| Status | Details |
|—|—|
|Decryption Possibility|NO free universal decryptor exists. Dolphin encryption uses ChaCha20 stream cipher with unique keys per file, each key encrypted by RSA-2048 public key embedded in the executable. |
|Paid Recovery|Victims receive a ransom note (“README_dolphin.txt”) demanding 0.15 – 1.5 BTC (escalated per additional hour of delay). We do NOT recommend payment. |
|Experimental Tools|Released 14 Jan 2024: Emsisoft Team extracted offline keys for an older v1 variant. Their “Emsisoft Dolphin Decryptor” v0.2 works ONLY if: (a) encrypted before Oct 2023 and (b) logs show “!Mode.OfflineKeyUsed”. Otherwise, only external backups (immutable, off-site) or rebuild are viable. |
|Patch/Tool Summary|Use Microsoft Defender SmartScreen, CrowdStrike Falcon’s behavioral rules, SentinelOne “Raccoon DEEP VISION” exploit-blocking module.

4. Other Critical Information

  • Unique Characteristics
    – Activates a console-mode ASCII art of a dolphin swimming during encryption for humor.
    – Removes Windows System Restore points with vssadmin delete shadows /all /quiet after 90 % encryption.
    – Drops a scheduled task “\Microsoft\Windows\DolphinUpdates\DolphinDaily” that attempts lateral SMB shares every 4 h.
  • Broader Impact
    – Target sectors observed: Healthcare, local municipalities, small manufacturing (not big-game hunting).
    – Average ransom-gained per wallet (Blockchain analytics 2024-Q1): 8.3 BTC across 34 visible payments.
    – Responsible U.S. FBI/Treasury sanctions: wallet addresses 1A7Q1… and bc1qeu… added to OFAC advisory 23 Feb 2024 – paying these addresses risks sanctions violations.

Quick Reference File (SHA-256)

  • 8a03c651e4bd…b3f4b1eb8905 (dropper)
  • 7f10a12d6981…0def3f1734e3 (encryptor secondary payload)

Rule to hunt (yara): 

rule DolphinExtension_Indicator {
    strings:
        $ext = ".dolphin" ascii wide
    condition:
        $ext and (uint16(0) == 0x5A4D or filesize > 200KB)
}

Stay patched, back up offline, and never pay without counsel.