Introduction
Sandhills Medical Foundation (SC) and Laurel Eye Clinic (PA) have confirmed a security incident that has directly impacted the sensitive protected health information (PHI) of 169,000 patients. Characterized as an "encryption-based cyber incident," this event bears the hallmark of a targeted ransomware operation. For healthcare defenders, this is not merely a data breach; it is a disruption of care continuity. The encryption of medical records and systems creates immediate life-safety risks beyond standard data privacy concerns. This post outlines the technical mechanics of such encryption attacks and provides the detection signatures and remediation steps necessary to secure healthcare environments against similar threats.
Technical Analysis
While the specific CVE vulnerability used for initial access has not been publicly disclosed in the breach notice, the classification of the incident as "encryption-based" indicates a deployment of ransomware payload following an initial compromise.
- Threat Vector: Ransomware (Encryption-based).
- Attack Chain (Defensive View):
- Initial Access: Likely via phishing, credential theft, or exploitation of unpatched external services (e.g., VPN, RDP).
- Execution: malicious PowerShell scripts or execution of a binaries payload.
- Defense Evasion: Deletion of Volume Shadow Copies to prevent recovery.
- Impact: Bulk encryption of files (documents, databases, images) with specific extensions.
- Exploitation Status: Active exploitation confirmed. Encryption-based attacks are a top-tier threat to the Healthcare and Public Health (HPH) sector according to CISA warnings.
In healthcare environments, attackers specifically target systems storing PHI (PACS, EHR) because the operational urgency incentivizes payment. Defenders must look for the precursors to encryption—specifically the manipulation of backup mechanisms.
Detection & Response
Detection of encryption-based incidents relies on identifying the "prep work" attackers do before locking files. The most reliable indicators are attempts to delete backups (Shadow Copies) and the mass execution of encryption utilities.
Sigma Rules
The following rules target the disabling of Windows recovery mechanisms and the mass execution of suspicious processes associated with ransomware deployment.
---
title: Potential Ransomware Activity - VSSAdmin Shadow Copy Deletion
id: 550d9a23-0f72-4e3a-a8c5-1d2f3b4c5d6e
status: experimental
description: Detects attempts to delete Volume Shadow Copies using vssadmin.exe, a common precursor to ransomware encryption to prevent data recovery.
references:
- https://attack.mitre.org/techniques/T1490/
author: Security Arsenal
date: 2025/04/10
tags:
- attack.impact
- attack.t1490
logsource:
category: process_creation
product: windows
detection:
selection:
Image|endswith: '\vssadmin.exe'
CommandLine|contains: 'delete shadows'
condition: selection
falsepositives:
- Legitimate administrative backup maintenance (rare)
level: critical
---
title: Potential Ransomware Activity - WMIC Shadow Storage Deletion
id: 7a3f1c82-9e4b-4d67-bc12-3e5a8f901234
status: experimental
description: Detects attempts to delete Volume Shadow Copies using wmic.exe, an alternative method used by ransomware operators.
references:
- https://attack.mitre.org/techniques/T1490/
author: Security Arsenal
date: 2025/04/10
tags:
- attack.impact
- attack.t1490
logsource:
category: process_creation
product: windows
detection:
selection:
Image|endswith: '\wbem\wmic.exe'
CommandLine|contains:
- 'shadowcopy delete'
- 'shadowstorage delete'
condition: selection
falsepositives:
- System administration scripts
level: high
KQL (Microsoft Sentinel / Defender)
This KQL hunt queries for the deletion of shadow copies and suspicious PowerShell execution patterns often used to launch encryption payloads across the network.
// Hunt for Shadow Copy Deletion and Suspicious PowerShell Execution
let ProcessEvents = DeviceProcessEvents
| where Timestamp >= ago(7d);
// Detect vssadmin or wmic deletion attempts
ProcessEvents
| where FileName in~ ("vssadmin.exe", "wmic.exe")
| where ProcessCommandLine contains "delete"
and (ProcessCommandLine contains "shadow" or ProcessCommandLine contains "shadowstorage")
| union (
ProcessEvents
| where FileName =~ "powershell.exe"
// Common patterns in ransomware deployment scripts
| where ProcessCommandLine matches regex @"-EncodedCommand\s+"
or ProcessCommandLine contains "-ExecutionPolicy Bypass"
)
| project Timestamp, DeviceName, InitiatingProcessAccountName, FileName, ProcessCommandLine, FolderPath
| order by Timestamp desc
Velociraptor VQL
This VQL artifact hunts for the execution of backup deletion utilities and checks for the presence of common ransomware note files on the endpoint.
-- Hunt for ransomware precursors and artifacts
SELECT Pid, Name, CommandLine, Exe, Username, CreateTime
FROM pslist()
WHERE Name =~ 'vssadmin'
OR Name =~ 'wmic'
OR CommandLine =~ 'delete.*shadow'
UNION
-- Check for common ransomware note patterns in user directories
SELECT FullPath, Size, Mtime, Atime
FROM glob(globs='/*/*/README*.txt', root='/')
WHERE Size < 50000
AND Mtime < now() - 1h
Remediation Script (PowerShell)
This script performs an immediate defensive check: it verifies if the Volume Shadow Copy Service (VSS) is operational and if any recent shadow copies were deleted. In a ransomware incident, restoring VSS is critical for recovery.
# Check VSS Health and Recent Shadow Copy Status
Write-Host "Checking Volume Shadow Copy (VSS) Service Status..." -ForegroundColor Cyan
$vssService = Get-Service -Name VSS -ErrorAction SilentlyContinue
if ($null -eq $vssService) {
Write-Host "[ALERT] VSS Service not found on this system." -ForegroundColor Red
} else {
Write-Host "VSS Service Status: $($vssService.Status)" -ForegroundColor Green
if ($vssService.Status -ne 'Running') {
Write-Host "[ACTION] Attempting to start VSS Service..."
Start-Service -Name VSS -ErrorAction Stop
}
}
# List existing Shadow Copies to verify availability for recovery
Write-Host "\nCurrent Shadow Copies:" -ForegroundColor Cyan
try {
vssadmin list shadows
} catch {
Write-Host "[ERROR] Failed to list shadows. Permissions may be restricted or VSS corrupt." -ForegroundColor Red
}
# Check Event Log for recent VSS deletion events (Event ID 10 in Microsoft-Windows-VSS)
Write-Host "\nChecking for recent VSS Deletion events (Last 24h)..." -ForegroundColor Cyan
Get-WinEvent -FilterHashtable @{LogName='Microsoft-Windows-VSS/Operational'; ID=10; StartTime=(Get-Date).AddHours(-24)} -ErrorAction SilentlyContinue |
Select-Object TimeCreated, Message | Format-List
Remediation
Immediate containment and recovery are paramount in encryption-based incidents affecting healthcare data.
- Isolation: Immediately disconnect affected systems (Sandhills and Laurel Eye Clinic infrastructure) from the network to prevent lateral movement, but avoid shutting down critical servers if live memory forensics are needed.
- Credential Reset: Assume domain admin credentials have been compromised. Force a password reset for all privileged accounts and enforce MFA immediately.
- Backup Integrity: Verify that offline backups are untouched. Attackers often target backup appliances first. Use the PowerShell script above to check VSS health on Windows endpoints.
- Vulnerability Patching: Even without a confirmed CVE in the public notice, conduct an immediate external vulnerability scan. Focus on VPN concentrators, RDP gateways, and known IOCs associated with ransomware groups (e.g., LockBit, BlackCat/ALPHV).
- Vendor Advisory: Review guidance from the HHS Health Sector Cybersecurity Coordination Center (HC3) regarding ransomware in healthcare.
Related Resources
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