Detect Brute Force in Splunk
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/
SPL Detection Query
index=wineventlog sourcetype="WinEventLog:Security" (EventCode=4625 OR EventCode=4624)
| eval LogonType=mvindex(split(coalesce(LogonType, "0"), " "), 0)
| where LogonType IN ("3", "10")
| eval EventType=case(EventCode="4624", "Success", EventCode="4625", "Failure", true(), "Unknown")
| bin _time span=10m
| stats
count(eval(EventType="Failure")) as FailedCount,
count(eval(EventType="Success")) as SuccessCount,
dc(TargetUserName) as DistinctTargets,
values(TargetUserName) as TargetAccounts,
earliest(_time) as FirstAttempt,
latest(_time) as LastAttempt
by _time, IpAddress, ComputerName
| where FailedCount >= 10
| eval AttackPattern=case(
DistinctTargets > 5 AND FailedCount >= 10, "Password Spray",
DistinctTargets <= 2 AND FailedCount >= 20, "Account Brute Force",
true(), "Brute Force")
| eval SuccessAfterFailure=if(SuccessCount > 0, "YES", "NO")
| eval RiskScore=case(
SuccessAfterFailure="YES", 100,
AttackPattern="Password Spray" AND FailedCount >= 50, 85,
AttackPattern="Account Brute Force" AND FailedCount >= 100, 75,
FailedCount >= 20, 60,
true(), 40)
| table FirstAttempt, LastAttempt, ComputerName, IpAddress, FailedCount, SuccessCount,
DistinctTargets, TargetAccounts, AttackPattern, SuccessAfterFailure, RiskScore
| sort - RiskScore, - FailedCountDetects brute force attacks using Windows Security Event IDs 4624 (successful logon) and 4625 (failed logon) with a 10-minute sliding window. Classifies attack patterns as Password Spray (many accounts, moderate attempts) or Account Brute Force (few accounts, many attempts). Assigns a risk score from 0-100 with highest priority given when a successful logon follows a burst of failures from the same source IP. LogonType 3 (Network) and 10 (RemoteInteractive) are filtered to focus on remote authentication brute force rather than local interactive failures.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Misconfigured service accounts with expired or recently changed passwords generating automatic logon failures in batch
- Legitimate penetration testing or red team exercises against authorized targets
- Users who forget their password and repeatedly attempt login before resetting
- Load balancers or multi-hop proxies causing multiple logon attempts to appear from a single source IP
- Password manager applications failing to update cached credentials after a password rotation
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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