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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_MAL_CN_Wocao_Agent_Powershell_Dropper

Strings from PowerShell dropper of CSharp version of Agent

APT / threat actorSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Fox-IT SRT
Date
2019-12-20
Modified
2023-12-05
Score / Quality
75 / 85

What this rule detects

Strings from PowerShell dropper of CSharp version of Agent

It defines 3 patterns (3 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
apt-mal-cn-wocao-agent-powershell-dropper.yarDetection Rule License 1.1
rule SIGNATURE_BASE_APT_MAL_CN_Wocao_Agent_Powershell_Dropper
{
	meta:
		description = "Strings from PowerShell dropper of CSharp version of Agent"
		author = "Fox-IT SRT"
		id = "833ce607-56a9-5580-bbd1-e72392945fec"
		date = "2019-12-20"
		modified = "2023-12-05"
		reference = "https://www.fox-it.com/en/news/whitepapers/operation-wocao-shining-a-light-on-one-of-chinas-hidden-hacking-groups/"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_op_wocao.yar#L24-L38"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "19f56e69685ae8c13b9dd884f8322915835c16e2c6313f01f9fa447218419108"
		score = 75
		quality = 85
		tags = ""

	strings:
		$a = "function format([string]$source)"
		$b = "foreach($c in $bb){$tt = $tt + [char]($c -bxor"
		$c = "[agent]::Main($args);"

	condition:
		1 of them
}

Strings (3 patterns)

IdentifierTypeValueModifiers
$atext"function format([string]$source)"
$btext"foreach($c in $bb){$tt = $tt + [char]($c -bxor"
$ctext"[agent]::Main($args);"

Condition

1 of them

In plain words (Heuristic)

  • At least 1 patterns in the rule must match.

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References

Licence & attribution

Author: Fox-IT SRT

Source repository: Signature Base (Florian Roth / Nextron) @ 94a1c48d7a

Licence: Detection Rule License 1.1 (repository licence)

Original rule

Mirrored via YARA Forge 20260927, which prefixes rule names with the source and adds normalised meta fields.

Rule id: 833ce607-56a9-5580-bbd1-e72392945fec

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