Detect CVE-2026-33825 - Microsoft Defender Insufficient Access Control Exploitation in Microsoft Sentinel
Detects exploitation attempts targeting CVE-2026-33825, an insufficient granularity of access control vulnerability (CWE-1220) in Microsoft Defender. This KEV-listed vulnerability allows attackers to bypass Defender access controls, potentially disabling protections, modifying exclusions, or tampering with security configurations without appropriate privilege levels.
MITRE ATT&CK
KQL Detection Query
let DefenderTamperEvents = SecurityEvent
| where TimeGenerated > ago(24h)
| where EventID in (4657, 4670, 4907)
| where ObjectName has_any ("Windows Defender", "MsMpEng", "WinDefend", "SecurityHealthService")
| where AccessMask in ("0x2", "0x4", "0x20", "0x40");
let DefenderConfigChanges = DeviceRegistryEvents
| where TimeGenerated > ago(24h)
| where RegistryKey has_any (
"HKLM\\SOFTWARE\\Policies\\Microsoft\\Windows Defender",
"HKLM\\SOFTWARE\\Microsoft\\Windows Defender"
)
| where ActionType in ("RegistryValueSet", "RegistryValueDeleted", "RegistryKeyCreated")
| where InitiatingProcessAccountName !in ("SYSTEM", "TrustedInstaller")
| where InitiatingProcessFileName !in~ ("MsMpEng.exe", "NisSrv.exe", "SecurityHealthService.exe", "MpCmdRun.exe");
let DefenderServiceChanges = DeviceProcessEvents
| where TimeGenerated > ago(24h)
| where (FileName =~ "sc.exe" and ProcessCommandLine has_any ("WinDefend", "MsMpEng", "SecurityHealthService") and ProcessCommandLine has_any ("stop", "config", "delete", "disable"))
or (FileName =~ "powershell.exe" and ProcessCommandLine has_any ("Set-MpPreference", "Add-MpPreference", "Remove-MpPreference", "Disable-WindowsOptionalFeature") and ProcessCommandLine has_any ("-DisableRealtimeMonitoring", "ExclusionPath", "ExclusionProcess", "-DisableIOAVProtection", "-DisableBehaviorMonitoring"))
or (FileName =~ "reg.exe" and ProcessCommandLine has "Windows Defender" and ProcessCommandLine has_any ("add", "delete"));
union DefenderTamperEvents, DefenderConfigChanges, DefenderServiceChanges
| extend AccountName = coalesce(InitiatingProcessAccountName, SubjectUserName, ""), HostName = coalesce(DeviceName, Computer, "")
| summarize EventCount=count(), FirstSeen=min(TimeGenerated), LastSeen=max(TimeGenerated), Commands=make_set(coalesce(ProcessCommandLine, ObjectName, RegistryKey), 20) by AccountName, HostName, bin(TimeGenerated, 5m)
| where EventCount >= 1
| extend AlertTitle = "CVE-2026-33825 - Suspected Defender Access Control Bypass"
| project LastSeen, FirstSeen, AlertTitle, AccountName, HostName, EventCount, CommandsDetects registry modifications, service configuration changes, and PowerShell commands consistent with exploitation of CVE-2026-33825 — bypassing Defender access controls to disable protections or add exclusions without appropriate privileges.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate IT administrators using approved tooling to manage Defender policy via Group Policy or MDM
- Authorized security operations teams running Defender health checks or remediation scripts
- Endpoint management platforms (SCCM, Intune, Tanium) modifying Defender configuration as part of policy enforcement
- Antivirus migration tools that temporarily disable Defender during third-party AV installation
Other platforms for CVE-2026-33825
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Disable Defender Real-Time Monitoring via PowerShell (CVE-2026-33825 Simulation)
Expected signal: Sysmon EventID 1 (process creation) for powershell.exe with CommandLine containing Set-MpPreference and DisableRealtimeMonitoring; Windows Defender Operational EventID 5001 (real-time protection disabled); DeviceProcessEvents in MDE showing the PowerShell invocation
- Test 2Add Defender Exclusion Path via PowerShell
Expected signal: Sysmon EventID 1 for powershell.exe with Add-MpPreference and ExclusionPath in CommandLine; Defender Operational EventID 5007 (configuration changed) with new exclusion path; registry modification to HKLM\SOFTWARE\Microsoft\Windows Defender\Exclusions\Paths
- Test 3Stop WinDefend Service via sc.exe
Expected signal: Sysmon EventID 1 (process creation) for sc.exe with CommandLine 'sc stop WinDefend'; Windows System EventID 7036 (WinDefend service stopped); Security EventID 4689 (process exit) for MsMpEng.exe if service fully stops; Defender Operational EventID 5001
- Test 4Modify Defender Registry Key to Disable Antispyware
Expected signal: Sysmon EventID 13 (registry value set) with TargetObject HKLM\SOFTWARE\Policies\Microsoft\Windows Defender\DisableAntiSpyware and Details=DWORD (0x00000001); Security EventID 4657 for registry write to Defender policy key; Defender Operational EventID 5007
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