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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_MAL_CN_Wocao_Agent_Csharp

Strings from 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 CSharp version of Agent

It defines 8 patterns (7 text, 1 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
apt-mal-cn-wocao-agent-csharp.yarDetection Rule License 1.1
rule SIGNATURE_BASE_APT_MAL_CN_Wocao_Agent_Csharp
{
	meta:
		description = "Strings from CSharp version of Agent"
		author = "Fox-IT SRT"
		id = "e5212226-a82d-558d-abb4-43ad7848764e"
		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#L2-L22"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "e77fcd2ac0c21db54563b15466962a775a5e8ef73cedb3af5cd00d5b0d615e4c"
		score = 75
		quality = 85
		tags = ""

	strings:
		$a = "mysend(client_sock, new byte[] { 0x16, 0x00 }, 2);" ascii wide
		$b = "Dns.GetHostAddresses(sip.Remove(sip.Length - 1));" ascii wide
		$c = "Port = 256 * buf[4] + buf[5];" ascii wide
		$d = "Port = 256 * buf[AddrLen] + buf[AddrLen + 1];" ascii wide
		$e = "StartTransData(CliSock" ascii wide
		$f = "static void ForwardTransmit(object ft_data)" ascii wide
		$key = "0x4c, 0x1b, 0x68, 0x0b, 0x6a, 0x18, 0x09, 0x41, 0x5a, 0x36, 0x1f, 0x56, 0x26, 0x2a, 0x03, 0x44, 0x7d, 0x5f, 0x03, 0x7b, 0x07, 0x6e, 0x03, 0x77, 0x30, 0x70, 0x52, 0x42, 0x53, 0x67, 0x0a, 0x2a" ascii wide
		$key_raw = { 4c1b680b6a1809415a361f56262a03447d5f037b076e03773070524253670a2a }

	condition:
		1 of them
}

Strings (8 patterns)

IdentifierTypeValueModifiers
$atext"mysend(client_sock, new byte[] { 0x16, 0x00 }, 2);"ascii wide
$btext"Dns.GetHostAddresses(sip.Remove(sip.Length - 1));"ascii wide
$ctext"Port = 256 * buf[4] + buf[5];"ascii wide
$dtext"Port = 256 * buf[AddrLen] + buf[AddrLen + 1];"ascii wide
$etext"StartTransData(CliSock"ascii wide
$ftext"static void ForwardTransmit(object ft_data)"ascii wide
$keytext"0x4c, 0x1b, 0x68, 0x0b, 0x6a, 0x18, 0x09, 0x41, 0x5a, 0x36, 0x1f, 0x56, 0x26, 0x2a, 0x03, 0x44, 0x7d, 0x5f, 0x03, 0x7b, 0x07, 0x6e, 0x03, 0x77, 0x30, 0x70, 0x5 …ascii wide
$key_rawhex{ 4c1b680b6a1809415a361f56262a03447d5f037b076e03773070524253670a2a }

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: e5212226-a82d-558d-abb4-43ad7848764e

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