enc_robbinhood

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RobbinHood (a.k.a. “enc_robbinhood”) Ransomware – Community Defense Guide

Last updated: 2024-05-XX

TECHNICAL BREAKDOWN

1. File Extension & Renaming Patterns

  • Confirmed extension appended to every encrypted file:
    .enc_robbinhood (lower case; a 19-byte string including the leading dot).
  • Renaming convention:
    Original name → <original_full_name>.enc_robbinhood
    Example: Annual_Report.xlsx becomes Annual_Report.xlsx.enc_robbinhood.
    No e-mail address, victim-ID, or random hex is inserted—only the static suffix.
    The ransomware deliberately skips SYSTEM, Program Files, ProgramData, and Windows trees to keep the OS bootable so victims can read the ransom note.

2. Detection & Outbreak Timeline

  • First public samples: 2019-04-23 (uploaded to VirusTotal and ID-Ransomware).
  • Major waves:
    – Apr-Jul 2019: High-volume attacks against U.S. municipalities (Greenville NC, Albany NY, Lafayette CO, etc.).
    – Nov 2019: Campaign that hit multiple hospitals.
    – 2020-2021: Sporadic, lower-volume sightings; still circulating in 2024 via affiliate tooling.

3. Primary Attack Vectors

  • Most common historical entry:
    – Open or brute-forced RDP followed by manual deployment by the operator.
  • Secondary vector observed:
    – Spear-phish e-mail carrying malicious ZIP → BAT/HTA dropper → RobbinHood loader.
  • Lateral movement / privilege escalation inside the network:
    – Uses the legitimate Gigabyte “GDRV.SYS” driver (CVE-2018-19320, 0-day at the time) or the susceptible “RTCore64.sys” (CVE-2019-18935) to disable DSE and load a custom, unsigned kernel driver.
    – That driver kills 280+ processes and 40+ services (AV, backup agents, sql, exchange, vss, etc.) and deletes all Volume-Shadow-Copies with vssadmin.
    – SMB is not exploited for automatic worm-like spreading; instead the attacker manually targets high-value machines through compromised domain credentials.

REMEDIATION & RECOVERY STRATEGIES

1. PREVENTION

  • Perimeter
    – Block TCP/3389 (RDP) at the firewall; if remote access is required, force VPN + MFA + NLA + account lockout policy.
    – Disable SMBv1 company-wide (RobbinHood does not need it, but lateral actors still use EternalBlue-style toolkits).
  • E-mail / end-user
    – Aggressive quarantine rules for archive formats (ZIP, 7Z) and HTA/BAT/PS1 macros.
    – User-awareness drills focusing on “double-extension” files (e.g., Invoice.pdf.bat).
  • Endpoint / Server hardening
    – Apply the 2020-09 Windows DRV patch (KB4577015) and 2021-05 cumulative updates that blacklist the vulnerable GIGABYTE & MICRO-STAR drivers.
    – Turn on Windows Defender Credential Guard, enable ASR rules “Block credential stealing…”, and use Microsoft’s Driver Block List (HVCI).
    – Continuous, offline (immutable) backups—3-2-1 rule: 3 copies, 2 media, 1 off-site/offline; backup appliance account must not be domain-joined.

2. REMOVAL / CLEAN-UP (step-by-step)

  1. Physically isolate the affected machine(s) from the network (pull Ethernet/Wi-Fi).
  2. Boot into Safe Mode with Networking or use a Linux live-USB to avoid loading the malicious driver.
  3. Delete persistence artefacts:
  • C:\Windows\System32\drivers\robnlg*.sys (randomised name; signed, but dropped)
  • Scheduled task \Microsoft\Windows\Setup\Scripts\Cleanup (deletes event-logs)
  1. Remove the rogue service entry:
    sc query type= kernel | findstr robnl → note the short name → sc delete <name>
  2. Update and run a reputable AV engine with current RobbinHood signatures (Microsoft, Sophos, ESET, Kaspersky all detect as Ransom:Win32/RobbinHood).
  3. Reboot normally, re-install/whitelist your regular security stack, patch CVE-2018-19320/19321, re-image if policy requires.
    NOTE: Only after complete sanitation should you attempt file-recovery so that decrypted data does not get re-encrypted.

3. FILE DECRYPTION & RECOVERY

  • No flaw has been published for the ransomware’s RSA-2048 + AES-256 implementation; therefore files cannot be decrypted without the attacker’s private key.
  • No free decryptor exists (hecked with TheNoMoreRansom Project, Emsisoft, Avast, Bitdefender).
  • Recovery options:
    a. Restore from backup that was offline during the incident.
    b. If shadow copies were not wiped (rare but possible in abort runs), use an admin cmd:
    vssadmin list shadows → diskshadow → expose %shadow_ID% X: → copy data out.
    c. Engage a reputable incident-response firm to negotiate or validate the purchased decryptor should payment be the last-resort (legal dept + cyber-insurance involvement required).
    d. File-recovery carving tools (PhotoRec, R-Studio) can retrieve some deleted originals from unallocated space if the ransomware overwrote rather than wiped, but expect <10 % success.

4. OTHER CRITICAL INFORMATION

  • Unique characteristics:
    – Weaponises a legitimate, signed kernel driver to turn off security—uncommon for 2019 and still evades some “next-gen” AV that ignores ring-0.
    – Ransom note (DecryptionReadMe.html) tries the bizarre claim that “paying within a certain time helps poor people” to build moral pressure.
    – Flat fee demanded (3–13 BTC depending on victim size) instead of per-machine unlock key.
  • Broader impact:
    – More than 20 U.S. cities paralysed in 2019; average downtime 3–6 weeks.
    – Prompted CISA Alert AA19-131A and several state emergency declarations; became a textbook example for cyber-insurance underwriting requirements (offline backups, MFA on RDP).

KEY TAKEAWAY

RobbinHood is human-operated and destructive, but preventable: close RDP to the Internet, enforce MFA, back up offline, and block the vulnerable drivers it needs to cripple defences. Share this guide and stay safe!