Chinese Hacktool Set - file hydra.exe

Hunt Hypothesis

This detection targets adversary behavior involving the deployment of hydra.exe, a known Chinese hack tool often utilized for credential brute-forcing or lateral movement within compromised networks. Proactively hunting for this artifact in Azure Sentinel is critical to identify early-stage reconnaissance activities that may precede more severe data exfiltration or privilege escalation attempts, even when initial alerts are flagged as low severity.

YARA Rule

rule hydra_7_4_1_hydra {
	meta:
		description = "Chinese Hacktool Set - file hydra.exe"
		author = "Florian Roth"
		reference = "http://tools.zjqhr.com/"
		date = "2015-06-13"
		hash = "3411d0380a1c1ebf58a454765f94d4f1dd714b5b"
	strings:
		$s1 = "%d of %d target%s%scompleted, %lu valid password%s found" fullword ascii
		$s2 = "[%d][smb] Host: %s Account: %s Error: ACCOUNT_CHANGE_PASSWORD" fullword ascii
		$s3 = "hydra -P pass.txt target cisco-enable  (direct console access)" fullword ascii
		$s4 = "[%d][smb] Host: %s Account: %s Error: PASSWORD EXPIRED" fullword ascii
		$s5 = "[ERROR] SMTP LOGIN AUTH, either this auth is disabled" fullword ascii
		$s6 = "\"/login.php:user=^USER^&pass=^PASS^&mid=123:incorrect\"" fullword ascii
	condition:
		uint16(0) == 0x5a4d and filesize < 1000KB and 2 of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 6 string patterns in its detection logic.

References

• http://tools.zjqhr.com/
• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the Chinese Hacktool Set - file hydra.exe detection rule, including suggested filters or exclusions:

• Password Reset via Hydra Command-Line Tool

  • Scenario: System administrators frequently utilize the open-source hydra tool (often distributed as a standalone executable named hydra.exe) to perform brute-force testing against internal Active Directory or LDAP services during security audits. This legitimate activity involves the execution of hydra.exe from temporary directories (e.g., %TEMP% or C:\Tools\Hydra) with arguments targeting specific ports like 389 (LDAP) or 445 (SMB).
  • Filter/Exclusion: Create an exclusion for processes named hydra.exe where the file path contains \Tools\, \Security\, or %TEMP%, and the command line includes flags such as -m ldap, -m smb, or -t ssh. Additionally, whitelist the specific SHA-256 hash of the known legitimate Hydra binary used by your organization.

• Scheduled Database Performance Monitoring

  • Scenario: A scheduled job running under the SYSTEM account executes a custom monitoring utility named hydra.exe (part of an internal database performance suite) to analyze SQL Server connection pools and latency metrics every 15 minutes. This tool is installed in a standard application directory but may be flagged if the detection logic assumes hydra.exe is exclusively a Chinese hacktool without verifying the parent process or installation path.
  • Filter/Exclusion: Exclude alerts where the file path matches C:\Program Files\InternalDBMonitor\bin\hydra.exe and the parent process is TaskScheduler.exe. Verify that the executable possesses a valid digital signature from your internal corporate Certificate Authority (CA).

• Third-Party Endpoint Security Agent Updates