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kaandgnshkaandgnsh/Claude-Blue/skills/active-directory-security/gpo-security-review/SKILL.md

gpo-security-review

Skill0 starsChanged 14 days agoMITView on GitHub

Review Group Policy for security baseline compliance, dangerous settings, GPP passwords, excessive edit rights and malicious GPO changes; detect GPO-based malware deployment via event 5136. Use when auditing GPOs, comparing to Microsoft/CIS baselines, or investigating ransomware deployed through Group Policy.

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SKILL.md

GPO Security Review

Collection

Get-GPO -All | Select-Object DisplayName, Id, ModificationTime, GpoStatus
Get-GPOReport -All -ReportType Xml -Path C:\review\gpos.xml
# Who can edit each GPO
Get-GPO -All | ForEach-Object { $g=$_; Get-GPPermission -Guid $g.Id -All |
  Where-Object { $_.Permission -in 'GpoEdit','GpoEditDeleteModifySecurity' } |
  Select-Object @{n='GPO';e={$g.DisplayName}}, Trustee, Permission }
# GPP cpassword remnants (MS14-025)
Select-String -Path "\\$env:USERDNSDOMAIN\SYSVOL\*\Policies\*\*.xml" -Pattern 'cpassword' -List

Compare with Microsoft Security Compliance Toolkit baselines using Policy Analyzer.

What to flag

  • Non-Tier-0 principals with edit rights on GPOs linked to DCs/Tier 0 OUs (or at domain root).
  • GPP XML containing cpassword (decryptable, key is public).
  • Startup/logon scripts or Scheduled Task (GPP) items pointing to writable shares.
  • Settings weakening security: WDigest enabled, LM hash storage, NTLMv1 allowed (LmCompatibilityLevel < 5), SMB signing not required on DCs, LDAP signing/channel binding not enforced, Defender disabled/exclusions, Restricted Groups adding broad groups to local Administrators.
  • Audit policy GPO missing or weaker than recommended (windows-event-log-analysis).
  • Orphaned/unlinked GPOs and SYSVOL folders without GPO objects.

Detecting malicious GPO changes

5136 (directory object modified) on groupPolicyContainer objects, especially gPCMachineExtensionNames / versionNumber changes; 5137 new GPO; 5141 deleted. File changes in SYSVOL\...\Machine\Preferences\ScheduledTasks\ScheduledTasks.xml or Scripts\ (file integrity monitoring on SYSVOL).

SecurityEvent
| where EventID == 5136 and ObjectClass == "groupPolicyContainer"
| project TimeGenerated, SubjectUserName, ObjectDN, AttributeLDAPDisplayName, AttributeValue

Output

GPO | Linked to | Finding | Setting/ACL | Risk | Recommended change | Owner

Related skills

ad-privileged-access-review, ransomware-response, endpoint-hardening

References

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