Detect Account Access Removal in Google Chronicle
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/
YARA-L Detection Query
rule t1531_account_access_removal {
meta:
author = "Argus Detection Engineering"
description = "Detects T1531 Account Access Removal via account deletion, disabling, lockout, or credential manipulation. Ransomware families LockerGoga, MegaCortex, and Akira use this technique to impede IR before encryption. LAPSUS$ removed global admin accounts to lock organizations out entirely."
severity = "HIGH"
priority = "HIGH"
mitre_attack_tactic = "Impact"
mitre_attack_technique = "T1531"
false_positives = "Authorized IT account lifecycle management, deprovisioning automation, PAM credential rotation"
version = "1.0"
events:
(
$e.metadata.event_type = "USER_DELETION" or
$e.metadata.event_type = "USER_ACCOUNT_DISABLED" or
$e.metadata.event_type = "USER_CHANGE_PASSWORD" or
$e.metadata.event_type = "USER_ACCOUNT_LOCKED" or
(
$e.metadata.event_type = "PROCESS_LAUNCH" and
re.regex(
$e.target.process.command_line,
`(?i)(net[\s]+user[\s\S]+/del|Set-LocalUser|Set-ADAccountPassword|Disable-ADAccount|Remove-ADUser|Remove-LocalUser|userdel[\s]+|usermod[\s]+-L)`
)
)
)
not re.regex($e.target.user.userid, `.*\$`)
outcome:
$risk_score = max(
if($e.metadata.event_type = "USER_DELETION", 90,
if($e.metadata.event_type = "USER_ACCOUNT_DISABLED", 70,
if($e.metadata.event_type = "USER_CHANGE_PASSWORD", 60,
if($e.metadata.event_type = "USER_ACCOUNT_LOCKED", 30, 40))))
)
$host = $e.principal.hostname
$actor = $e.principal.user.userid
$target_user = $e.target.user.userid
$event_type = $e.metadata.event_type
$command = $e.target.process.command_line
condition:
$e
}Chronicle YARA-L 2.0 rule detecting T1531 Account Access Removal using UDM event types USER_DELETION, USER_ACCOUNT_DISABLED, USER_CHANGE_PASSWORD, USER_ACCOUNT_LOCKED, and PROCESS_LAUNCH with regex matching on account manipulation command lines. Computer accounts (userid ending in $) are excluded via re.regex filter. Outcome variables expose risk scoring and actor/target context for downstream SOAR enrichment and alert triage. The rule fires per-event (condition: $e) for immediate detection without requiring aggregation.
Data Sources
Required Tables
False Positives & Tuning
- Authorized Active Directory lifecycle automation via PowerShell DSC, Azure AD Connect sync, or HR system integrations (Workday, BambooHR) that propagate account state changes — these generate USER_ACCOUNT_DISABLED events at scale during organizational changes and may require principal.application filtering
- Chronicle UDM normalization may map routine end-user self-service password changes through identity providers (Okta, Azure AD SSPR) to USER_CHANGE_PASSWORD — consider adding not $e.principal.application = "SelfServicePasswordReset" to reduce noise
- Privileged access management platforms (CyberArk, BeyondTrust) performing scheduled credential rotation for service accounts will generate USER_CHANGE_PASSWORD events — correlate $host against a Chronicle reference list of known PAM server hostnames to suppress
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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