Detect Password Guessing in Google Chronicle
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/
YARA-L Detection Query
rule T1110_001_password_guessing {
meta:
author = "Detection Engineering"
description = "Detects password guessing via high-volume Windows authentication failures (logon failure, Kerberos pre-auth, NTLM) from the same source IP to the same host within a 10-minute window."
mitre_attack_tactic = "Credential Access"
mitre_attack_technique = "T1110.001"
mitre_attack_technique_name = "Brute Force: Password Guessing"
severity = "MEDIUM"
priority = "MEDIUM"
reference = "https://attack.mitre.org/techniques/T1110/001/"
false_positives = "Service accounts with expired credentials, authorized password audit tools"
events:
$e.metadata.event_type = "USER_LOGIN"
$e.security_result.action = "BLOCK"
$e.metadata.vendor_name = "Microsoft"
$e.principal.ip != ""
not $e.principal.ip = "127.0.0.1"
not $e.principal.ip = "::1"
$e.target.user.userid != ""
not $e.target.user.userid = "-"
not re.regex($e.target.user.userid, `(?i)^anonymous logon$`)
$source_ip = $e.principal.ip
$target_host = $e.target.hostname
match:
$source_ip, $target_host over 10m
condition:
#e >= 10
}Chronicle YARA-L 2.0 rule detecting password guessing by counting failed USER_LOGIN events (mapped from Windows Event IDs 4625, 4771, 4776 via UDM normalization) originating from the same source IP targeting the same host within a 10-minute sliding window. Requires 10 or more blocked login attempts to fire.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate users repeatedly failing multi-factor authentication challenges due to misconfigured authenticator apps or expired TOTP codes, generating blocked login events in rapid succession
- Service accounts running automated ETL jobs or scheduled scripts with credentials that expired mid-execution, causing a burst of authentication failures at predictable job start times
- IT operations teams running automated runbooks or configuration management tools (e.g., Ansible, Puppet) that include credential validation steps across multiple accounts during system provisioning
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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