Detect Account Access Removal in CrowdStrike LogScale
Adversaries may interrupt availability of system and network resources by inhibiting access to accounts utilized by legitimate users. Accounts may be deleted, locked, or manipulated (changed credentials, revoked permissions) to remove access. In Windows, the Net utility, Set-LocalUser, and Set-ADAccountPassword PowerShell cmdlets may be used to modify user accounts. In Linux, the passwd utility may be used to change passwords. Ransomware families such as LockerGoga, MegaCortex, and Akira use this technique to impede incident response before completing their encryption objective. LAPSUS$ has removed global admin accounts to lock organizations out of all access.
MITRE ATT&CK
- Tactic
- Impact
- Technique
- T1531 Account Access Removal
- Canonical reference
- https://attack.mitre.org/techniques/T1531/
LogScale Detection Query
(#event_simpleName = "UserAccountDeleted"
OR #event_simpleName = "UserAccountDisabled"
OR #event_simpleName = "UserAccountPasswordChanged"
OR #event_simpleName = "UserAccountLockout"
OR (#event_simpleName = "ProcessRollup2"
AND CommandLine = /(?i)(net\s+user\s+\S+\s+\/del|Set-LocalUser|Set-ADAccountPassword|Disable-ADAccount|Remove-ADUser|Remove-LocalUser|userdel\s+|usermod\s+-L)/)
)
| RiskScore := case{
#event_simpleName = "UserAccountDeleted", 90;
CommandLine = /(?i)net\s+user.*\/del/, 90;
CommandLine = /(?i)(Set-LocalUser|Set-ADAccountPassword|Disable-ADAccount|Remove-ADUser|Remove-LocalUser)/, 75;
#event_simpleName = "UserAccountDisabled", 70;
#event_simpleName = "UserAccountPasswordChanged", 60;
CommandLine = /(?i)(userdel\s|usermod\s+-L)/, 50;
#event_simpleName = "UserAccountLockout", 30;
*, 40
}
| ActionType := case{
#event_simpleName = "UserAccountDeleted", "AccountDeleted";
#event_simpleName = "UserAccountDisabled", "AccountDisabled";
#event_simpleName = "UserAccountPasswordChanged", "PasswordChanged";
#event_simpleName = "UserAccountLockout", "AccountLockedOut";
*, "ProcessBasedAccountOp"
}
| sort(field=RiskScore, order=desc, limit=500)
| select([timestamp, ComputerName, UserName, TargetUserName, CommandLine, #event_simpleName, ActionType, RiskScore])CrowdStrike LogScale (Falcon) query detecting T1531 Account Access Removal via Falcon sensor user account telemetry events (UserAccountDeleted, UserAccountDisabled, UserAccountPasswordChanged, UserAccountLockout) and ProcessRollup2 process execution events with regex matching against net user /delete, PowerShell Active Directory cmdlets, and Linux account management utilities (userdel, usermod -L). Risk-scored 30–90 with computed ActionType field for triage. Uses case{} assignment syntax for risk and action classification.
Data Sources
Required Tables
False Positives & Tuning
- CrowdStrike Falcon UserAccountDeleted and UserAccountDisabled events may fire for machine and computer accounts during Active Directory cleanup operations — append | TargetUserName != /.*\$/ to exclude computer accounts (trailing dollar sign) if high-volume false positives are observed
- Automated IT operations using PowerShell remoting, SCCM, or Intune that invoke Disable-ADAccount or Set-ADAccountPassword for routine service account rotation will generate ProcessRollup2 matches — enrich with ParentBaseFileName to identify known management tool parent processes and build a suppression list
- PAM solutions (CyberArk, Delinea) managing privileged credential vaults generate UserAccountPasswordChanged events on rotation schedules — correlate ComputerName against a reference list of known PAM server hostnames to suppress expected rotation activity
Other platforms for T1531
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 1Delete Local Windows User Account via Net Command
Expected signal: Security Event ID 4726 (A user account was deleted) with SubjectUserName=current admin account and TargetUserName=df00techtest. Sysmon Event ID 1 for net.exe and net1.exe with CommandLine containing 'user df00techtest /delete'. Security Event ID 4720 (account created) for the creation step.
- Test 2Disable Local User Account via PowerShell Set-LocalUser
Expected signal: Security Event ID 4725 (A user account was disabled) with TargetUserName=df00techtest2. Sysmon Event ID 1 for powershell.exe with CommandLine containing 'Set-LocalUser' and '-Enabled $false'. PowerShell ScriptBlock Log Event ID 4104 with the full Set-LocalUser command.
- Test 3Bulk Account Password Change Simulation via Net Command
Expected signal: Security Event ID 4723 (password change attempt) and/or 4724 (password reset) for df00techtest3. Sysmon Event ID 1 for net.exe with CommandLine containing 'user df00techtest3 NewL0ckedP@ssw0rd!'. The password value itself will appear in process creation logs if command line auditing is enabled.
- Test 4Linux Account Lock via passwd -l
Expected signal: Linux auditd records: syscall=execve for useradd and passwd commands with argv showing '-l df00techtest_linux'. Syslog entries in /var/log/auth.log or /var/log/secure: 'passwd: password changed for df00techtest_linux'. If auditd is configured with USER_MGMT rules, generates AUDIT_USER_MGMT events for account modification.
References (9)
- https://attack.mitre.org/techniques/T1531/
- https://www.carbonblack.com/2019/03/22/tau-threat-intelligence-notification-lockergoga-ransomware/
- https://unit42.paloaltonetworks.com/born-this-way-origins-of-lockergoga/
- https://web.archive.org/web/20230608061141/https://www.obsidiansecurity.com/blog/saas-ransomware-observed-sharepoint-microsoft-365/
- https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4726
- https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4725
- https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4724
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1531/T1531.md
- https://www.microsoft.com/en-us/security/blog/2022/03/22/dev-0537-criminal-actor-targeting-organizations-for-data-exfiltration-and-destruction/
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