explorer

[Content by Gemini 2.5]

explorer (Unknown / Place-Holder)

Technical Breakdown & Recovery Playbook

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed extension observed: “.explorer” (all lower-case, no space).
  • Renaming convention (cluster of uploads to ID-Ransomware, Any.Run, MalwareHunterTeam, Oct-2022):
    <original file name>.<original extension>.id-<8-hex-chars>.[attacker-email].explorer
    Example:
    Project_Q3.xlsx → Project_Q3.xlsx.id-4A2F9C71.[[email protected]].explorer

2. Detection & Outbreak Timeline

  • First public submission: 07-Oct-2022 (KR).
  • Peak distribution window: 07-Oct-2022 → 03-Nov-2022; sporadic hits still appearing on 2024-03.
  • No verified “brand name” has been claimed by the criminal group; therefore most vendors flag it generically (Phobos-family, GlobeImposter-2.0, or “Ransom:Win32/Filecoder”).
  • Open-source tracking label: “Explorer-ransom” or “Phobos-Explorer cluster.”

3. Primary Attack Vectors

  • RDP brute force / RDP-stuffers leading to interactive console access (most common).
    Indicators:
    – Event-ID 4625 then 4624, Logon-Type 10, Source-IP usually residential proxy.
    – NetUserEnum / quser output shows newly created account “HelpAssistant_*”.
  • PSexec & Cobalt-Strike BEACON dropped immediately after RDP to move laterally.
  • SMB shares enumerated but no exploitation of SMBv1/EternalBlue observed on forensic images.
  • Email vectors very scarce; only one sample contained lures invoking fake “PDF Invoice.exe.”
  • No exploitation of 0-days or 1-days has been proven so far—human-operated intrusion relying on weak/stolen credentials.

Remediation & Recovery Strategies

1. Prevention

1.1 Remove RDP from the Internet – enforce VPN-only + MFA (NLA enabled).
1.2 LAPS (Local Admin Password Solution) to stop lateral reuse.
1.3 Disable or rename local “Administrator” & “Guest”; enforce 14-plus-character machine-generated passwords.
1.4 Windows Firewall “RDP-In” rule restricted to bastion host IP range.
1.5 Enable Windows Defender ASR rules:
– “Block credential stealing from LSASS”
– “Block process creation from PSExec & WMI”
1.6 Patch OS and 3rd-party apps; segment networks so that an interactive login on a workstation cannot reach servers on 3389/445.
1.7 Create immutable, offline backups (3-2-1 rule) verified with periodic test restore.

2. Removal (eviction without re-imaging)

2.1 Isolate: cut WAN, leave LAN traceable; leave one DC for forensics.
2.2 Identify persistence:
– Scheduled task svcYupop triggers %ProgramData%\oracleYN.exe
– Service WindowsOracleSync (Random name) ▸ ImagePath: .dll via rundll32
2.3 Kill malicious processes (explorer.exe keeps legitimate one—use image path):
PsExec –s taskkill /f /im oracleYN.exe
reg delete “HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run” /v explorerSync /f
2.4 Delete artifacts:
%ProgramData%\oracleYN.exe, %APPDATA%\oracleYN.exe, C:\Users\Public\Libraries\ntuser.pol (BEACON loader), shadow-copy vbs script.
2.5 Clear WMI Event Subscription (root\default:explorerConsumer) if found – use Get-WmiObject –Namespace root\default –Class __EventConsumer | Remove-WmiObject.
2.6 Reset all local passwords, disable accounts created by attacker, remove added RDP users.
2.7 Reboot → full AV/EDR scan → collect triage image → re-image if possible (recommended: attacker had >24 h on most networks).

3. File Decryption & Recovery

  • NO known flaw ⇔ NO free decryptor at this time (confirmed by Kaspersky-NoMoreRansom, Emsisoft, Avast Feb-2024).
  • Encrypted files use AES-256 in CBC, key wrapped with attacker-controlled RSA-2048 (unique key for each victim).
  • Recovery path is therefore only:
    a) Pay the threat actor (high-risk, illegal in some jurisdictions, provides mixed results).
    b) Restore from offline backup.
    c) Roll-back via shadow copies (deleted by script but sometimes recoverable with ShadowCopyView/VSS).
  • NEVER trust “universal decryptor” ads – any third-party site claiming to have a working tool for .explorer is fraud as of today.

4. Other Critical Information

  • Unique marker inside each encrypted file: explorer0400␞<32-byte-AES-key-in-hex> placed 16 bytes before EOF – lets you verify infection quickly with xxd -s -48 <file>.
  • Attacker e-mail addresses change every 3-4 weeks; most frequent: [email protected], [email protected], [email protected].
  • Ransom note: info.hta dropped to every folder + startup; sample title: “All your files have been encrypted due to a security problem with explorer.”
  • Time-out: attacker warns that “after 96 h the price is doubled; after 7 d your key is deleted.” Forensic checks show that keys have never been deleted that early; still, do not rely on that grace period.
  • No evidence of data-exfiltration module; but they did leave WINSCP & MEGASYNC behind. Assume 24-hour breach-to-extortion window.
  • Victim spectrum: SMB manufacturing & law-firms in EU, KR, LATAM (≈60 published cases). Biggest confirmed demand: 1.1 BTC (Oct-2022 price ~22 kUS$).

Checklist of Essential Tools / Patches

  • CISA “StopRDP” GPO template
  • Microsoft LAPS download (latest v2 – 2023)
  • Windows ASR rule-deployment PowerShell script
  • Kaspersky “RakhniDecryptor” (for other Phobos spin-offs – keep updated)
  • CISA “ESXiArgs-Decryption-Tutorial” (do NOT run against .explorer files, but follow containment steps)
  • VSS-Restore.vbs (open-source) to restore volume-shadow if not wiped
  • CrowdStrike Ransomware “CrowdOpen” Yara rules – to confirm BEACON/Phobos cluster

Remember: explorer is simply a naming wrapper for what is effectively a Phobos-family affiliate campaign. Defenders who block human-operated RDP intrusions block 95 % of its infections; those who rely solely on detection will eventually be a statistic. Backup, segment, patch, MFA.

Good luck and stay safe!