Detect Reversible Encryption in CrowdStrike LogScale
Adversaries may enable the AllowReversiblePasswordEncryption property on Active Directory user accounts to gain access to plaintext credentials. When enabled, Active Directory stores user passwords in a reversibly encrypted form (G$RADIUSCHAP in userParameters) rather than as one-way hashes. An adversary with SYSTEM access can decrypt these passwords using four components from AD user structures and LSA secrets. Adversaries can set this via PowerShell (Set-ADUser -AllowReversiblePasswordEncryption $true), Local Group Policy, or Fine-Grained Password Policy (FGPP) if Domain Functional Level is Windows Server 2008+.
MITRE ATT&CK
- Technique
- T1556 Modify Authentication Process
- Sub-technique
- T1556.005 Reversible Encryption
- Canonical reference
- https://attack.mitre.org/techniques/T1556/005/
LogScale Detection Query
// Detection 1: PowerShell enabling reversible encryption via process events
#event_simpleName = "ProcessRollup2"
| ImageFileName = /(?i)(powershell|pwsh)\.exe$/
| CommandLine = /(?i)(AllowReversiblePasswordEncryption|ENCRYPTED_TEXT_PASSWORD_ALLOWED|Set-ADDefaultDomainPasswordPolicy|New-ADFineGrainedPasswordPolicy)/
| CommandLine = /(?i)(\$true|\btrue\b|enable)/
| select([@timestamp, ComputerName, UserName, ImageFileName, CommandLine, ProcessStartTime, ParentProcessId, TargetProcessId])
| sort(field=@timestamp, order=desc)
// Detection 2: Script block logging for reversible encryption (run separately)
#event_simpleName = "ScriptControlScanTelemetry"
| ScriptContent = /(?i)(AllowReversiblePasswordEncryption|ENCRYPTED_TEXT_PASSWORD_ALLOWED)/
| ScriptContent = /(?i)(\$true|\btrue\b|Set-ADUser|Set-ADDefaultDomainPasswordPolicy)/
| select([@timestamp, ComputerName, UserName, ScriptContent, SHA256HashData])
| sort(field=@timestamp, order=desc)CrowdStrike LogScale (CQL) query detecting reversible password encryption enablement via PowerShell process execution (ProcessRollup2) with command lines invoking AD reversible encryption parameters, and via ScriptControlScanTelemetry for script block content analysis. Windows Security Event 4738 correlation should be performed via the Falcon event search for endpoint-sourced Windows Event logs.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate IT automation running PowerShell AD cmdlets as part of user provisioning pipelines where reversible encryption is required for a specific application integration
- Security assessment tooling such as PingCastle or Purple Knight that enumerates AllowReversiblePasswordEncryption settings across the domain during AD health audits
- Domain Group Policy or DSC (Desired State Configuration) management scripts that evaluate current password policy posture and log or report reversible encryption states
Other platforms for T1556.005
Testing Methodology
Validate this detection against 3 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 1Enable Reversible Password Encryption on a Test Account
Expected signal: Security Event ID 4738: User Account Changed for testuser_atomic, with UserAccountControl value showing ENCRYPTED_TEXT_PASSWORD_ALLOWED. PowerShell ScriptBlock Log Event ID 4104 with the Set-ADUser command. Sysmon Event ID 1 for powershell.exe with AllowReversiblePasswordEncryption in CommandLine.
- Test 2Audit Accounts with Reversible Encryption Enabled
Expected signal: PowerShell ScriptBlock Log Event ID 4104 with the Get-ADUser filter query. Active Directory query events. Security Event ID 4662 for directory object access on enumerated user objects.
- Test 3Set Reversible Encryption via Fine-Grained Password Policy
Expected signal: Security Event ID 4738/5136 (DS Object Modified): Fine-Grained Password Policy object creation with msDS-PasswordReversibleEncryptionEnabled attribute set. PowerShell ScriptBlock Log Event ID 4104 with New-ADFineGrainedPasswordPolicy.
References (5)
- https://attack.mitre.org/techniques/T1556/005/
- https://docs.microsoft.com/en-us/windows/security/threat-protection/security-policy-settings/store-passwords-using-reversible-encryption
- https://adsecurity.org/?p=2053
- http://blog.teusink.net/2009/08/passwords-stored-using-reversible.html
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1556.005/T1556.005.md
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