Detect Brute Force in CrowdStrike LogScale
Adversaries may use brute force techniques to gain access to accounts when passwords are unknown or when password hashes are obtained. Without knowledge of the password for an account or set of accounts, an adversary may systematically guess the password using a repetitive or iterative mechanism. Brute forcing passwords can take place via interaction with a service that will check the validity of those credentials or offline against previously acquired credential data, such as password hashes. Threat actors including Fox Kitten, APT38, APT41, OilRig, and Turla have used brute force techniques against RDP, SSH, SMB, and web services.
MITRE ATT&CK
- Tactic
- Credential Access
- Technique
- T1110 Brute Force
- Canonical reference
- https://attack.mitre.org/techniques/T1110/
LogScale Detection Query
// Requires Windows endpoint authentication events via Falcon sensor or FDR
#event_simpleName = /^UserLogon(Failed)?2$/
| LogonType = /^(3|10)$/
| FailureEvent := if(#event_simpleName == "UserLogonFailed2", 1, 0)
| SuccessEvent := if(#event_simpleName == "UserLogon2", 1, 0)
| bucket(span=10m, function=[
sum(FailureEvent, as=FailedCount),
sum(SuccessEvent, as=SuccessCount),
dcount(UserName, as=DistinctTargets),
collect(UserName, limit=20, as=TargetAccounts)
], field=[ComputerName, RemoteAddressIP4])
| FailedCount >= 10
| AttackPattern := case(
DistinctTargets > 5, "Password Spray",
FailedCount >= 20, "Account Brute Force",
default="Brute Force"
)
| SuccessAfterFailure := if(SuccessCount > 0, "YES", "NO")
| RiskScore := case(
SuccessAfterFailure == "YES", 100,
AttackPattern == "Password Spray" and FailedCount >= 50, 85,
AttackPattern == "Account Brute Force" and FailedCount >= 100, 75,
FailedCount >= 20, 60,
default=40
)
| sort(RiskScore, order=desc, limit=100)Detects brute force attacks using CrowdStrike Falcon UserLogon2 (success) and UserLogonFailed2 (failure) sensor events filtered to network and remote-interactive logon types (3, 10). Buckets events into 10-minute windows per host and remote IP, requiring at least 10 failures. Computes attack pattern classification and risk score with success-after-failure as the highest priority indicator.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate remote administration tools such as PSExec or custom WinRM automation scripts cycling through multiple authentication attempts from a single management workstation IP when executing against a host list in sequence
- Domain controller Kerberos pre-authentication failures during Kerberos ticket renewal or KDC fallback scenarios where the Falcon sensor logs interim failures from internal DC IPs before successful TGT issuance
- Falcon sensor coverage validation tests or tabletop exercises where the security team deliberately simulates brute force from a known test machine to verify alerting pipeline functionality
Other platforms for T1110
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 1RDP Brute Force Simulation with Crowbar
Expected signal: On the target Windows host: Security Event ID 4625 (LogonType=10, RemoteInteractive) for each failed attempt, with IpAddress showing the attacker IP. If lockout policy is enabled and threshold exceeded: Event ID 4740 (account locked out). Network logs: multiple TCP connections to port 3389 from attacker IP in rapid succession.
- Test 2SSH Brute Force with Hydra
Expected signal: On the target Linux host: /var/log/auth.log entries 'Failed password for root from <attacker-ip> port <port> ssh2'. If using auditd: type=USER_AUTH msg entries with res=failed. Sysmon for Linux (if deployed): Event ID 3 (network connection) on the attacker side. SIEM via Syslog forwarder: linux_secure sourcetype or syslog with 'Failed password' pattern.
- Test 3Active Directory Password Spray with PowerShell
Expected signal: On Domain Controller: Security Event ID 4625 (LogonType=3, Network) for each failed account, SubStatus 0xC000006D (wrong password) or 0xC000006A (wrong password for correct username). Caller IP address will be the workstation running the spray. Security Event ID 4771 (Kerberos pre-auth failure) if using Kerberos authentication. Timing will show evenly spaced failures 500ms apart — distinctive automated tool pattern.
- Test 4NTLM Brute Force via SMB with CrackMapExec
Expected signal: Target Windows host: Security Event ID 4625 (LogonType=3, Network, AuthenticationPackageName=NTLM) for each failed credential. Domain Controller: Security Event ID 4776 (NTLM authentication attempt, error code 0xC000006A for wrong password) with Workstation field showing attacker hostname. Network: multiple TCP connections to port 445 (SMB) from attacker IP. CME results show [*] for failure and [+] for success in its output.
References (10)
- https://attack.mitre.org/techniques/T1110/
- https://www.microsoft.com/en-us/security/blog/2021/09/27/foggyweb-targeted-nobelium-malware-leads-to-persistent-backdoor/
- https://learn.microsoft.com/en-us/defender-for-identity/compromised-credentials-alerts
- https://learn.microsoft.com/en-us/azure/active-directory/reports-monitoring/reference-sign-ins-error-codes
- https://www.dragos.com/wp-content/uploads/CRASHOVERRIDE2018.pdf
- https://www.trendmicro.com/en_us/research/20/l/pawn-storm-lack-of-sophistication-as-a-strategy.html
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1110/T1110.md
- https://github.com/SigmaHQ/sigma/tree/master/rules/windows/builtin/security
- https://www.cisa.gov/sites/default/files/2024-09/aa24-249a-foreign-threat-actor-conducting-large-scale-spear-phishing-campaign-with-rdp-attachments.pdf
- https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4625
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