Detect Password Guessing in Splunk
Adversaries with no prior knowledge of legitimate credentials within the system or environment may guess passwords to attempt access to accounts. Without knowledge of the password for an account, an adversary may opt to systematically guess the password using a repetitive or iterative mechanism. An adversary may guess login credentials without prior knowledge of system or environment passwords during an operation by using a list of common passwords. Password guessing may or may not take into account the target's policies on password complexity or use policies that may lock accounts out after a number of failed attempts. Commonly targeted services include SSH, RDP, SMB, LDAP, Kerberos, FTP, MSSQL, MySQL, VNC, and web management portals. Threat actors such as APT28, APT29, Emotet, and tools like CrackMapExec have leveraged this technique extensively.
MITRE ATT&CK
- Tactic
- Credential Access
- Technique
- T1110 Brute Force
- Sub-technique
- T1110.001 Password Guessing
- Canonical reference
- https://attack.mitre.org/techniques/T1110/001/
SPL Detection Query
index=wineventlog (sourcetype="WinEventLog:Security" OR sourcetype="XmlWinEventLog:Security")
(EventCode=4625 OR EventCode=4771 OR EventCode=4776)
| eval TargetAccount=case(
EventCode=4625, lower(mvindex('TargetUserName', 0)),
EventCode=4771, lower(mvindex('TargetUserName', 0)),
EventCode=4776, lower(mvindex('TargetUserName', 0)),
true(), "unknown"
)
| eval SourceIP=case(
EventCode=4625, coalesce(IpAddress, src_ip),
EventCode=4771, coalesce(IpAddress, src_ip),
EventCode=4776, coalesce(SourceWorkstation, src_ip),
true(), "unknown"
)
| eval DetectionType=case(
EventCode=4625, "Windows Logon Failure",
EventCode=4771, "Kerberos Pre-Auth Failure",
EventCode=4776, "NTLM Auth Failure",
true(), "Unknown"
)
| where TargetAccount!="" AND TargetAccount!="-" AND TargetAccount!="anonymous logon"
| where SourceIP!="" AND SourceIP!="-" AND SourceIP!="127.0.0.1" AND SourceIP!="::1"
| bucket _time span=10m
| stats
count as FailureCount,
dc(TargetAccount) as DistinctAccounts,
values(TargetAccount) as Accounts,
values(DetectionType) as DetectionTypes,
earliest(_time) as FirstSeen,
latest(_time) as LastSeen
by _time, host, SourceIP
| where FailureCount >= 10
| eval Severity=case(
FailureCount >= 50, "High",
FailureCount >= 20, "Medium",
true(), "Low"
)
| eval AttackPattern=if(DistinctAccounts > 3, "Password Spray Likely", "Password Guessing")
| table FirstSeen, LastSeen, host, SourceIP, FailureCount, DistinctAccounts, Accounts, DetectionTypes, Severity, AttackPattern
| sort - FailureCountDetects password guessing activity using Windows Security Event logs ingested into Splunk. Monitors for Event ID 4625 (Logon Failure), 4771 (Kerberos Pre-Auth Failure), and 4776 (NTLM Credential Validation). Aggregates failures per source IP and host over 10-minute buckets, alerting when failure count exceeds 10. Distinguishes between targeted password guessing (single account, many attempts) and password spray (many accounts, fewer attempts per account) using the DistinctAccounts field.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Misconfigured service accounts with expired or incorrect passwords generating repeated authentication failures against domain controllers
- Vulnerability scanners or penetration testing tools (Nessus, Qualys, Rapid7) performing authenticated scans that fail due to incorrect test credentials
- End users who have forgotten their passwords attempting to log in multiple times before calling the help desk
- Automated IT processes or scripts using hardcoded credentials that have not been updated after a password rotation
Other platforms for T1110.001
Testing Methodology
Validate this detection against 5 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 Password Guessing with Hydra
Expected signal: Windows Security Event ID 4625 (Logon Failure) with LogonType=10 (RemoteInteractive) on the target system, source IP matching the attacker host. Multiple failures in rapid succession. Network flow logs showing repeated TCP connections to port 3389 from attacker IP.
- Test 2SMB Password Guessing with CrackMapExec
Expected signal: Windows Security Event ID 4625 (Logon Failure) with LogonType=3 (Network) and SubStatus 0xC000006A (wrong password) on the target DC/server. Event ID 4776 (NTLM validation failure) may also appear. Sysmon Event ID 3 on the attacker host showing outbound connections to port 445.
- Test 3SSH Password Guessing using Hydra on Linux
Expected signal: Linux syslog/auth.log entries: 'Failed password for <user> from <attacker_ip> port <port> ssh2' and 'Invalid user <user> from <attacker_ip>'. Multiple entries in rapid succession from attacker IP. Possible PAM failure events if auditd is configured.
- Test 4Windows Local Account Password Guessing via Net Use
Expected signal: Windows Security Event ID 4625 (Logon Failure) on the target host with LogonType=3 (Network), SubStatus=0xC000006A (wrong password), and source IP matching the test machine. Sysmon Event ID 1 on the attacker machine showing cmd.exe spawning with 'net use' command line. Security Event ID 4648 (logon with explicit credentials) may also appear.
- Test 5Azure AD / Office 365 Password Guessing via MSOLSpray
Expected signal: Azure AD SigninLogs / AADSignInLogs in Microsoft Sentinel: ResultType = 50126 (invalid username or password) or 50053 (account locked out), with repeated entries from same IP. UserAgent reflecting PowerShell/HTTP client. Office 365 Unified Audit Log: UserLoginFailed operation with ClientInfoString showing legacy auth client.
References (13)
- https://attack.mitre.org/techniques/T1110/001/
- https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4625
- https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4771
- https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4776
- https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4740
- https://www.microsoft.com/en-us/security/blog/2020/09/10/strontium-new-campaign/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1110.001/T1110.001.md
- https://github.com/dafthack/MSOLSpray
- https://github.com/byt3bl33d3r/CrackMapExec
- https://www.us-cert.gov/ncas/alerts/TA18-086A
- https://web.archive.org/web/20200302085133/https://www.cylance.com/content/dam/cylance/pages/operation-cleaver/Cylance_Operation_Cleaver_Report.pdf
- https://www.trendmicro.com/vinfo/us/security/news/cybercrime-and-digital-threats/emotet-now-spreads-via-wi-fi
- https://www.mandiant.com/resources/blog/apt29-microsoft-365
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