April 2026 Patch Tuesday: Adobe Reader RCE, Windows Defender BlueHammer, and Critical CVEs

---
title: Adobe Reader Spawning Shell - Potential CVE-2026-2998 Exploitation
id: a8d9a23-0f72-4e3a-a8c5-1d2f3b4c5d6e
status: experimental
description: Detects Adobe Acrobat Reader spawning suspicious child processes like cmd, powershell, or wscript, which is typical behavior following successful exploit of PDF vulnerabilities.
references:
  - https://krebsonsecurity.com/2026/04/patch-tuesday-april-2026-edition/
author: Security Arsenal
date: 2026/04/08
tags:
  - attack.initial_access
  - attack.t1566.001
logsource:
  category: process_creation
  product: windows
detection:
  selection_parent:
    ParentImage|endswith:
      - '\AcroRd32.exe'
      - '\Acrobat.exe'
  selection_child:
    Image|endswith:
      - '\cmd.exe'
      - '\powershell.exe'
      - '\pwsh.exe'
      - '\wscript.exe'
      - '\cscript.exe'
  condition: all of selection_*
falsepositives:
  - Legitimate administrative use of PDF forms or scripts (rare)
level: high
---
title: Potential Windows Defender BlueHammer Tamper Attempt
id: b7e3f1c82-9e4b-4d67-bc12-3e5a8f901234
status: experimental
description: Detects attempts to stop the WinDefend service or modify Defender registry keys, which could be indicative of BlueHammer weakness exploitation or defense evasion.
references:
  - https://krebsonsecurity.com/2026/04/patch-tuesday-april-2026-edition/
author: Security Arsenal
date: 2026/04/08
tags:
  - attack.defense_evasion
  - attack.t1562.001
logsource:
  category: process_creation
  product: windows
detection:
  selection_svc:
    CommandLine|contains:
      - 'sc stop WinDefend'
      - 'net stop WinDefend'
  selection_reg:
    CommandLine|contains:
      - 'reg add'
      - 'reg delete'
    CommandLine|contains:
      - 'SOFTWARE\Microsoft\Windows Defender'
      - 'SOFTWARE\Policies\Microsoft\Windows Defender'
  condition: 1 of selection_*
falsepositives:
  - Authorized IT administration disabling Defender for testing (should be rare in prod)
level: high

// Hunt for Adobe Reader spawning shells (CVE-2026-2998 indicators)
DeviceProcessEvents
| where Timestamp >= ago(1d)
| where InitiatingProcessFileName in~ ('AcroRd32.exe', 'Acrobat.exe')
| where FileName in~ ('cmd.exe', 'powershell.exe', 'pwsh.exe', 'wscript.exe', 'cscript.exe', 'mshta.exe')
| project Timestamp, DeviceName, AccountName, InitiatingProcessCommandLine, FileName, ProcessCommandLine, SHA256
| order by Timestamp desc

-- Hunt for suspicious child processes spawned by Adobe Reader
SELECT
  Pid,
  Name,
  CommandLine,
  Exe,
  Username,
  Parent.Pid AS ParentPid,
  Parent.Name AS ParentName,
  Parent.CommandLine AS ParentCmd
FROM pslist()
WHERE Parent.Name =~ "AcroRd32.exe"
  AND Name IN ("cmd.exe", "powershell.exe", "wscript.exe", "cscript.exe")

# Remediation Script for April 2026 Patch Tuesday
# Checks Adobe Version and Windows Update Status

Write-Host "[+] Starting April 2026 Patch Assessment..." -ForegroundColor Cyan

# 1. Check Adobe Acrobat Reader Version (Target: 24.002.20xxx or later)
$adobePath = "HKLM:\SOFTWARE\Adobe\Acrobat Reader\DC\Installer"
if (Test-Path $adobePath) {
    $adobeVersion = (Get-ItemProperty $adobePath).Version
    Write-Host "[+] Adobe Reader DC Version found: $adobeVersion" -ForegroundColor Yellow
    if ($adobeVersion -lt "24.002.20000") {
        Write-Host "[!] ALERT: Adobe Reader is vulnerable to CVE-2026-2998. Update immediately." -ForegroundColor Red
    } else {
        Write-Host "[+] Adobe Reader appears patched." -ForegroundColor Green
    }
} else {
    Write-Host "[-] Adobe Reader DC registry path not found." -ForegroundColor Gray
}

# 2. Check for Windows Defender Tampering (BlueHammer Context)
$defenderService = Get-Service -Name WinDefend -ErrorAction SilentlyContinue
if ($defenderService.Status -ne "Running") {
    Write-Host "[!] CRITICAL: Windows Defender is not running. Investigate BlueHammer or tampering." -ForegroundColor Red
} else {
    Write-Host "[+] Windows Defender is running." -ForegroundColor Green
}

# 3. List pending Windows Updates
$session = New-Object -ComObject Microsoft.Update.Session
$ searcher = $session.CreateUpdateSearcher()
$historyCount = $ searcher.GetTotalHistoryCount()
Write-Host "[+] Total Update History Count: $historyCount" -ForegroundColor Cyan
Write-Host "[+] Please ensure KB504xxxx (April 2026 Cumulative) is installed." -ForegroundColor Yellow