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Chinese Hacktool Set - file ustrrefadd.dll

yara LOW Yara-Rules
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This rule was pulled from an open-source repository and enriched with AI. Validate in a test environment before deploying to production.
View original rule at Yara-Rules →
Retrieved: 2026-07-15T11:00:00Z · Confidence: medium

Hunt Hypothesis

This hunt targets adversaries deploying the specific ustrrefadd.dll component of a Chinese hacktool suite to establish persistence or execute reconnaissance within Windows endpoints. Proactively hunting for this artifact in Azure Sentinel is critical because its low severity classification may cause it to be overlooked by automated alerts, allowing attackers to maintain a stealthy foothold before escalating their activities.

YARA Rule

rule ustrrefadd {
	meta:
		description = "Chinese Hacktool Set - file ustrrefadd.dll"
		author = "Florian Roth"
		reference = "http://tools.zjqhr.com/"
		date = "2015-06-13"
		hash = "b371b122460951e74094f3db3016264c9c8a0cfa"
	strings:
		$s0 = "E-Mail  : [email protected]" fullword ascii
		$s1 = "Homepage: http://www.luocong.com" fullword ascii
		$s2 = ": %d  -  " fullword ascii
		$s3 = "ustrreffix.dll" fullword ascii
		$s5 = "Ultra String Reference plugin v%d.%02d" fullword ascii
	condition:
		uint16(0) == 0x5a4d and filesize < 320KB and all of them
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

This rule contains 5 string patterns in its detection logic.

References

False Positive Guidance

Here are 5 specific false positive scenarios for the Chinese Hacktool Set - file ustrrefadd.dll detection rule, including suggested filters and exclusions:

Original source: https://github.com/Yara-Rules/rules/blob/main/malware/TOOLKIT_Chinese_Hacktools.yar