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COD3NYM_SUSP_OBF_NET_Reactor_Native_Stub_Jan24

Detects native packer stub for version 4.5-4.7 of .NET Reactor. A pirated copy of version 4.5 of this commercial obfuscation solution is used by various malware families like BlackBit, RedLine, AgentTesla etc.

Suspicious / huntingRedLineAgentteslaCod3nym detection-rulesDetection Rule License 1.1Compiles with YARA-X (with warnings)
Author
Jonathan Peters
Date
2024-01-05
Modified
2024-01-12
Score / Quality
70 / 80

What this rule detects

Detects native packer stub for version 4.5-4.7 of .NET Reactor. A pirated copy of version 4.5 of this commercial obfuscation solution is used by various malware families like BlackBit, RedLine, AgentTesla etc.

Associated malware family: RedLine, Agenttesla.

Targets: Windows PE.

It defines 1 patterns (0 text, 1 hex, 0 regex). YARA modules used: pe.

YARA-X says: warning[deprecated_field]: field `number_of_resources` is deprecated

Summary generated from the rule's metadata and condition.

Rule source

Includes the imports needed to compile it on its own.

susp-obf-net-reactor-native-stub-jan24.yarDetection Rule License 1.1
import "pe"

rule COD3NYM_SUSP_OBF_NET_Reactor_Native_Stub_Jan24
{
	meta:
		description = "Detects native packer stub for version 4.5-4.7 of .NET Reactor. A pirated copy of version 4.5 of this commercial obfuscation solution is used by various malware families like BlackBit, RedLine, AgentTesla etc."
		author = "Jonathan Peters"
		id = "529dce88-a81d-5a98-aa6c-1f1b739ad074"
		date = "2024-01-05"
		modified = "2024-01-12"
		reference = "https://notes.netbytesec.com/2023/08/understand-ransomware-ttps-blackbit.html"
		source_url = "https://github.com/cod3nym/detection-rules//blob/86a04c4594cb48895192aad4af164f21f568c136/yara/dotnet/obf_net_reactor.yar#L3-L16"
		license_url = "https://github.com/cod3nym/detection-rules//blob/86a04c4594cb48895192aad4af164f21f568c136/LICENSE.md"
		hash = "6e8a7adf680bede7b8429a18815c232004057607fdfbf0f4b0fb1deba71c5df7"
		logic_hash = "287273babd3cd6bc1986b018367317019f2249851a2c19fc83857f7ff0b90b54"
		score = 70
		quality = 80
		tags = ""

	strings:
		$op = {C6 44 24 18 E0 C6 44 24 19 3B C6 44 24 1A 8D C6 44 24 1B 2A C6 44 24 1C A2 C6 44 24 1D 2A C6 44 24 1E 2A C6 44 24 1F 41 C6 44 24 20 D3 C6 44 24 21 20 C6 44 24 22 64 C6 44 24 23 06 C6 44 24 24 8A C6 44 24 25 F7 C6 44 24 26 3D C6 44 24 27 9D C6 44 24 28 D9 C6 44 24 29 EE C6 44 24 2A 15 C6 44 24 2B 68 C6 44 24 2C F4 C6 44 24 2D 76 C6 44 24 2E B9 C6 44 24 2F 34 C6 44 24 30 BF C6 44 24 31 1E C6 44 24 32 E7 C6 44 24 33 78 C6 44 24 34 98 C6 44 24 35 E9 C6 44 24 36 6F C6 44 24 37 B4}

	condition:
		for any i in ( 0 .. pe.number_of_resources -1 ) : ( pe.resources [ i ] . name_string == "_\x00_\x00" ) and $op
}

Strings (1 patterns)

IdentifierTypeValueModifiers
$ophex{C6 44 24 18 E0 C6 44 24 19 3B C6 44 24 1A 8D C6 44 24 1B 2A C6 44 24 1C A2 C6 44 24 1D 2A C6 44 24 1E 2A C6 44 24 1F 41 C6 44 24 20 D3 C6 44 24 21 20 C6 44 24 …

Condition

for any i in ( 0 .. pe.number_of_resources -1 ) : ( pe.resources [ i ] . name_string == "_\x00_\x00" ) and $op

In plain words (Heuristic)

  • A for-loop checks a property over several matches or items.
  • Uses the pe module.
  • Pattern $op must be present.

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References

Sample hashes

Hashes of samples the author lists in the rule's meta (look them up in your threat-intelligence platform).

  • 6e8a7adf680bede7b8429a18815c232004057607fdfbf0f4b0fb1deba71c5df7

Licence & attribution

Author: Jonathan Peters

Source repository: Cod3nym detection-rules @ 86a04c4594

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: 529dce88-a81d-5a98-aa6c-1f1b739ad074

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