Gunra Ransomware Hits Healthcare: Detection, Hunting, and Hardening Guide After CISA/FBI Joint Advisory

---
title: Ransomware Impact Staging - Shadow Copy Deletion and Boot Recovery Tampering
id: 3f8a2c41-7b1e-4d59-9a2c-6e1f0b8d4a71
status: experimental
description: Detects deletion of Volume Shadow Copies and disabling of Windows boot recovery, a near-universal ransomware pre-encryption behavior observed in Gunra affiliate operations.
references:
  - https://attack.mitre.org/techniques/T1490/
  - https://www.cisa.gov/news-events/cybersecurity-advisories
author: Security Arsenal
date: 2026/02/10
tags:
  - attack.impact
  - attack.t1490
logsource:
  category: process_creation
  product: windows
detection:
  selection_vss:
    Image|endswith:
      - '\vssadmin.exe'
      - '\wmic.exe'
      - '\wbadmin.exe'
      - '\diskshadow.exe'
    CommandLine|contains:
      - 'delete shadows'
      - 'shadowcopy delete'
      - 'delete catalog'
      - 'delete shadows'
  selection_bcd:
    Image|endswith: '\bcdedit.exe'
    CommandLine|contains:
      - 'recoveryenabled no'
      - 'bootstatuspolicy ignoreallfailures'
  condition: selection_vss or selection_bcd
falsepositives:
  - Backup administrators running catalog cleanup during maintenance windows
  - Some backup software legitimately deletes oldest shadow copies
level: critical
---
title: Mass Encryption Behavior - Ransom Note and Encrypted File Creation Burst
id: 9c4d7e02-5a38-4f61-b83d-2e9a1c0f6b55
status: experimental
description: Detects high-volume file rename/write bursts combined with ransom note drops, consistent with Gunra encryptor execution on endpoints and file servers.
references:
  - https://attack.mitre.org/techniques/T1486/
author: Security Arsenal
date: 2026/02/10
tags:
  - attack.impact
  - attack.t1486
logsource:
  category: file_event
  product: windows
detection:
  selection_note:
    TargetFilename|contains:
      - 'README_FOR_DECRYPT'
      - 'R3ADM3'
      - 'HOW_TO_DECRYPT'
      - 'RESTORE_FILES'
      - 'DECRYPT_INSTRUCTION'
  selection_ext:
    TargetFilename|endswith:
      - '.encrt'
      - '.encrypted'
      - '.locked'
  condition: 1 of selection_*
falsepositives:
  - Rare; legitimate software does not mass-produce decrypt instruction files
level: high
---
title: ESXi Ransomware Staging - VM Process Termination via esxcli
id: 61a8f3d9-2c47-4e08-a1b6-8d5c3e7f2094
status: experimental
description: Detects bulk termination of running virtual machines on ESXi hosts via esxcli, a standard step before hypervisor-level encryption in ransomware operations targeting virtualization infrastructure.
references:
  - https://attack.mitre.org/techniques/T1486/
author: Security Arsenal
date: 2026/02/10
tags:
  - attack.impact
  - attack.t1486
logsource:
  category: process_creation
  product: linux
detection:
  selection:
    CommandLine|contains|all:
      - 'esxcli'
      - 'vm process kill'
  selection_kill_type:
    CommandLine|contains:
      - '--type=force'
      - '--type=hard'
      - '-t force'
  condition: selection and selection_kill_type
falsepositives:
  - Scripted VM power operations during datacenter maintenance
level: critical

// Hunt: Pre-encryption staging behaviors associated with Gunra-style ransomware affiliates
// Covers shadow copy deletion, recovery tampering, security tooling tampering, and log clearing
let stagingCmds = dynamic(["delete shadows", "shadowcopy delete", "delete catalog",
    "recoveryenabled no", "bootstatuspolicy ignoreallfailures",
    "wevtutil cl", "cipher /w"]);
union isfuzzy=true
(DeviceProcessEvents
| where TimeGenerated > ago(7d)
| where ProcessCommandLine has_any (stagingCmds)
| project TimeGenerated, DeviceName, AccountName, FileName, ProcessCommandLine,
          InitiatingProcessFileName, InitiatingProcessAccountName, ReportId),
(SecurityEvent
| where TimeGenerated > ago(7d)
| where EventID == 4688
| where CommandLine has_any (stagingCmds)
| project TimeGenerated, Computer, Account, NewProcessName, CommandLine,
          ParentProcessName)
| order by TimeGenerated desc;

// Companion hunt: anomalous outbound data volume from servers (exfiltration precursor to double extortion)
DeviceNetworkEvents
| where TimeGenerated > ago(3d)
| where DeviceType has "Server"
| where RemoteIPType == "Public"
| summarize TotalBytes = sum(BytesSent), Connections = dcount(RemoteUrl)
          by DeviceName, RemoteIP, bin(TimeGenerated, 1h)
| where TotalBytes > 500000000  // >500MB/hr from a server to a single public IP
| order by TotalBytes desc;

-- Hunt for ransomware staging artifacts: suspicious process execution and shadow copy state
-- Deploy across server and critical-endpoint fleet
SELECT Pid, Name, CommandLine, Exe, Username, CreateTime
FROM pslist()
WHERE CommandLine =~ '(?i)(vssadmin.*delete|bcdedit.*recoveryenabled|wevtutil cl|cipher.*/w|esxcli.*vm process kill)'
   OR Name =~ '(?i)(rclone|restic|megasync|winscp)\.exe'

-- Correlate with VSS state on the endpoint
SELECT * FROM execve(argv=['cmd', '/c', 'vssadmin list shadows'])

# Gunra Ransomware Readiness Check - run on Windows servers and endpoints via GPO/SCCM/Intune
# Verifies key defensive controls are in place; outputs findings for remediation

Write-Host "=== Ransomware Readiness Assessment ===" -ForegroundColor Cyan

# 1. Verify VSS is enabled and shadow copies exist
$shadows = Get-CimInstance Win32_ShadowCopy -ErrorAction SilentlyContinue
if ($shadows) { Write-Host "[OK] Shadow copies present: $($shadows.Count)" } 
else { Write-Host "[FAIL] No shadow copies found - verify VSS scheduling" -ForegroundColor Red }

# 2. Verify boot recovery is NOT disabled (bcdedit tampering check)
$bcd = bcdedit /enum {default} | Out-String
if ($bcd -match 'recoveryenabled\s+No') {
    Write-Host "[FAIL] Boot recovery DISABLED - possible tampering indicator" -ForegroundColor Red
} else { Write-Host "[OK] Boot recovery enabled" }

# 3. Verify Microsoft Defender tamper protection and real-time monitoring
$mp = Get-MpComputerStatus
if ($mp.RealTimeProtectionEnabled -and $mp.IsTamperProtected) {
    Write-Host "[OK] Defender real-time protection + tamper protection active"
} else { Write-Host "[FAIL] Defender RTP or Tamper Protection off" -ForegroundColor Red }

# 4. Verify Controlled Folder Access (ransomware file-write blocking)
$cf = Get-MpPreference | Select-Object -ExpandProperty EnableControlledFolderAccess
if ($cf -eq 1) { Write-Host "[OK] Controlled Folder Access: Enabled" }
elseif ($cf -eq 2) { Write-Host "[WARN] Controlled Folder Access: Audit mode only" -ForegroundColor Yellow }
else { Write-Host "[FAIL] Controlled Folder Access disabled" -ForegroundColor Red }

# 5. Check for attack surface reduction (ASR) rules commonly bypassed by ransomware affiliates
$asr = (Get-MpPreference).AttackSurfaceReductionRules_Ids
if ($asr.Count -ge 5) { Write-Host "[OK] $($asr.Count) ASR rules configured" }
else { Write-Host "[WARN] Few/no ASR rules deployed - enable ransomware-relevant ASR rules" -ForegroundColor Yellow }

# 6. Verify SMBv1 disabled (legacy lateral movement path)
$smb1 = Get-WindowsOptionalFeature -Online -FeatureName SMB1Protocol -ErrorAction SilentlyContinue
if ($smb1.State -eq 'Disabled') { Write-Host "[OK] SMBv1 disabled" }
else { Write-Host "[FAIL] SMBv1 enabled - disable immediately" -ForegroundColor Red }

# 7. Audit RDP exposure
$rdp = (Get-ItemProperty 'HKLM:\System\CurrentControlSet\Control\Terminal Server').fDenyTSConnections
if ($rdp -eq 1) { Write-Host "[OK] RDP disabled" }
else { Write-Host "[WARN] RDP enabled - confirm it is NOT internet-exposed and requires MFA/VPN" -ForegroundColor Yellow }

# 8. Check for common exfiltration tooling (should not exist on clinical/business servers)
$exfilTools = @('rclone.exe','megasync.exe','restic.exe','filezilla.exe')
foreach ($t in $exfilTools) {
    $found = Get-ChildItem -Path 'C:\Users','C:\ProgramData' -Filter $t -Recurse -ErrorAction SilentlyContinue -Depth 3
    if ($found) { Write-Host "[ALERT] Potential exfil tool found: $($found.FullName)" -ForegroundColor Red }
}