title: Potential Cisco FMC Deserialization Exploit CVE-2026-20131
id: a1b2c3d4-5678-90ef-gh12-345678901234
status: experimental
description: Detects potential exploitation attempts of Cisco Secure Firewall Management Center deserialization vulnerability via suspicious web requests or process execution.
references:
  - https://cisa.gov/known-exploited-vulnerabilities-catalog
author: Security Arsenal Research
date: 2026/04/20
tags:
  - attack.initial_access
  - cve.2026.20131
  - cisco.fmc
logsource:
  category: webserver
detection:
  selection:
    c-uri|contains:
      - '/api/fmc_config/v1/domain/'
      - '/api/fmc_platform/v1/auth/'
    cs-method: POST
  filter_legit:
    sc-status:
      - 200
      - 201
      - 404
  condition: selection and not filter_legit
falsepositives:
  - Legitimate administrative API calls
level: critical
---
title: SmarterMail Authentication Bypass Attempt CVE-2026-23760
id: b2c3d4e5-6789-01fg-hi23-456789012345
status: experimental
description: Detects suspicious authentication patterns associated with SmarterMail alternate path authentication bypass vulnerability.
references:
  - https://cisa.gov/known-exploited-vulnerabilities-catalog
author: Security Arsenal Research
date: 2026/04/20
tags:
  - attack.initial_access
  - cve.2026.23760
  - smartermail
logsource:
  category: webserver
detection:
  selection_uri:
    c-uri|contains:
      - '/Services/MAIL.asmx'
      - '/Services/svcMail.asmx'
  selection_method:
    cs-method: POST
  selection_keywords:
    c-body|contains:
      - 'AuthenticateUser'
      - 'GetUserInfo'
  condition: all of selection_*
falsepositives:
  - Legitimate mobile sync client usage
level: high
---
title: Ransomware Pre-Encryption Activity - VSSAdmin Shadow Copy Deletion
id: c3d4e5f6-7890-12gh-ij34-567890123456
status: stable
description: Detects commands used by THEGENTLEMEN affiliates to delete Volume Shadow Copies to prevent recovery.
author: Security Arsenal Research
date: 2026/04/20
tags:
  - attack.impact
  - attack.t1490
  - ransomware
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    Image|endswith:
      - '\vssadmin.exe'
      - '\wmic.exe'
    CommandLine|contains:
      - 'delete shadows'
      - 'shadowstorage delete'
  condition: selection
falsepositives:
  - System administration tasks (rare)
level: critical

// Hunt for THEGENTLEMEN lateral movement and staging indicators
// Looks for large file transfers and unusual administrative access
let TimeFrame = 1d;
DeviceProcessEvents
| where Timestamp > ago(TimeFrame)
| where ProcessName has "powershell.exe" or ProcessName has "cmd.exe"
| where ProcessCommandLine has "New-Object" or ProcessCommandLine has "Invoke-Expression" or ProcessCommandLine has "DownloadString"
| extend HostName = DeviceName
| join kind=inner (
    DeviceNetworkEvents
    | where Timestamp > ago(TimeFrame)
    | where RemotePort in (445, 135, 5985, 5986) // SMB, WMI, WinRM
) on HostName
| summarize StartTime=min(Timestamp), EndTime=max(Timestamp), Processes=makeset(ProcessCommandLine), RemoteIPs=makeset(RemoteIP), InitiatedProcessesCount=count() by HostName, AccountName
| where InitiatedProcessesCount > 10

<#
.SYNOPSIS
    THEGENTLEMEN Ransomware Hardening & Triage Script
.DESCRIPTION
    Checks for recent scheduled task creation (common persistence) and 
    verifies if critical VSS services are running or tampered with.
#>

Write-Host "[+] Starting T-Minus Detection Check for THEGENTLEMEN activity..." -ForegroundColor Cyan

# 1. Check for Scheduled Tasks created in the last 7 days (Persistence)
$DateCutoff = (Get-Date).AddDays(-7)
Write-Host "[!] Checking for Scheduled Tasks created/modified since $DateCutoff..." -ForegroundColor Yellow

Get-ScheduledTask | Where-Object { $_.Date -ge $DateCutoff } | ForEach-Object {
    $TaskName = $_.TaskName
    $TaskPath = $_.TaskPath
    $Action = $_.Actions.Execute
    Write-Host "[!] Suspicious/Recent Task Found: $TaskPath$TaskName" -ForegroundColor Red
    Write-Host "    Action: $Action" -ForegroundColor DarkGray
}

# 2. Check Volume Shadow Copy Service Status
Write-Host "[+] Checking VSS Service Status..." -ForegroundColor Yellow
$VssService = Get-Service -Name VSS -ErrorAction SilentlyContinue
if ($VssService) {
    if ($VssService.Status -ne "Running") {
        Write-Host "[CRITICAL] VSS Service is not running. Potential impact detected." -ForegroundColor Red
    } else {
        Write-Host "[OK] VSS Service is Running." -ForegroundColor Green
    }
} else {
    Write-Host "[ERROR] Could not retrieve VSS Service status." -ForegroundColor Red
}

# 3. Check for RDP Connections (Potential Lateral Movement)
Write-Host "[+] Checking recent RDP connections (Event ID 4624, Type 10)..." -ForegroundColor Yellow
Get-WinEvent -LogName Security -FilterXPath "*[System[(EventID=4624)]] and *[EventData[Data[@Name='LogonType']='10']]" -MaxEvents 10 -ErrorAction SilentlyContinue | Select-Object TimeCreated, @{n='User';e={$_.Properties[5].Value}}, @{n='IP';e={$_.Properties[18].Value}} | Format-Table -AutoSize

Write-Host "[+] Scan Complete. Review Red output immediately." -ForegroundColor Cyan


---

# Incident Response Priorities

**T-minus Detection Checklist (Pre-Encryption):**
1.  **Perimeter Log Audit:** Immediately search firewall and proxy logs for indicators of CVE-2026-20131 (Cisco FMC) exploitation or SmarterMail authentication bypass.
2.  **Process Monitoring:** Look for `powershell.exe` spawning from `w3wp.exe` (IIS) or `java.exe` (Cisco FMC backend) processes.
3.  **Data Staging:** Monitor for sudden increases in egress traffic, specifically RDP/SCP/FTP transfers occurring outside of business hours.

**Critical Assets at Risk:**
- **Exchange/Email Servers:** Used for initial access (SmarterMail) and intellectual property theft.
- **Active Directory Controllers:** Targeted for credential dumping (DCSync) using tools like Mimikatz or Cobalt Strike.
- **Backup Servers:** The first priority for encryption to prevent recovery.

**Containment Actions:**
1.  **Isolate:** Immediately disconnect Cisco FMC appliances from the internet if unpatched. Quarantine SmarterMail servers.
2.  **Reset Credentials:** Force resets for all privileged accounts (Domain Admins) if Cisco FMC or Email servers are suspected compromised.
3.  **Suspend MFA:** If MFA is managed via a compromised directory, temporarily enforce strict geo-blocking or suspend external access.

---

# Hardening Recommendations

**Immediate (24 Hours):**
- **Patch:** Apply the patch for **CVE-2026-20131** on all Cisco Secure Firewall Management Center instances immediately.
- **Patch:** Apply updates for **SmarterMail** to mitigate **CVE-2026-23760**. Disable access to `/Services/` endpoints from untrusted IP ranges if patching is delayed.
- **Block:** Block inbound internet access to TCP 443/80 on management interfaces of firewalls (enforce management-only VLANs).

**Short-term (2 Weeks):**
- **Architecture:** Implement a Secure Admin Architecture (SAA) where critical infrastructure management is not accessible via the public internet.
- **Segmentation:** Enforce strict micro-segmentation preventing Email servers from initiating RDP/WinRM connections to Domain Controllers.
- **EDR:** Deploy Endpoint Detection and Response (EDR) specifically covering Linux-based email gateways and firewall management centers, which are often blind spots for traditional Windows-only AV.