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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_MAL_NK_3CX_Malicious_Samples_Mar23_4

Detects decrypted payload loaded inside 3CXDesktopApp.exe which downloads info stealer

APT / threat actorSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
MalGamy (Nextron Systems)
Date
2023-03-29
Modified
2023-12-05
Score / Quality
80 / 85

What this rule detects

Detects decrypted payload loaded inside 3CXDesktopApp.exe which downloads info stealer

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
apt-mal-nk-3cx-malicious-samples-mar23-4.yarDetection Rule License 1.1
rule SIGNATURE_BASE_APT_MAL_NK_3CX_Malicious_Samples_Mar23_4
{
	meta:
		description = "Detects decrypted payload loaded inside 3CXDesktopApp.exe which downloads info stealer"
		author = "MalGamy (Nextron Systems)"
		id = "d11170df-570c-510c-80ec-39048acd0fbd"
		date = "2023-03-29"
		modified = "2023-12-05"
		reference = "https://twitter.com/WhichbufferArda/status/1641404343323688964?s=20"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/gen_mal_3cx_compromise_mar23.yar#L234-L249"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "851c2c99ebafd4e5e9e140cfe3f2d03533846ca16f8151ae8ee0e83c692884b7"
		logic_hash = "2fd56527a094b1f155cf33af402328835d4fb8aee9a058742d3e3763acef9e46"
		score = 80
		quality = 85
		tags = ""

	strings:
		$op1 = {41 69 D0 [4] 8B C8 C1 E9 ?? 33 C1 8B C8 C1 E1 ?? 81 C2 [4] 33 C1 43 8D 0C 02 02 C8 49 C1 EA ?? 41 88 0B 8B C8 C1 E1 ?? 33 C1 44 69 C2 [4] 8B C8 C1 E9 ?? 33 C1 8B C8 C1 E1 ?? 41 81 C0 [4] 33 C1 4C 0F AF CF 4D 03 CA 45 8B D1 4C 0F AF D7 41 8D 0C 11 49 C1 E9 ?? 02 C8}
		$op2 = {4D 0F AF CC 44 69 C2 [4] 4C 03 C9 45 8B D1 4D 0F AF D4 41 8D 0C 11 41 81 C0 [4] 02 C8 49 C1 E9 ?? 41 88 4B ?? 4D 03 D1 8B C8 45 8B CA C1 E1 ?? 33 C1}
		$op3 = {33 C1 4C 0F AF C7 8B C8 C1 E1 ?? 4D 03 C2 33 C1}

	condition:
		2 of them
}

Strings (3 patterns)

IdentifierTypeValueModifiers
$op1hex{41 69 D0 [4] 8B C8 C1 E9 ?? 33 C1 8B C8 C1 E1 ?? 81 C2 [4] 33 C1 43 8D 0C 02 02 C8 49 C1 EA ?? 41 88 0B 8B C8 C1 E1 ?? 33 C1 44 69 C2 [4] 8B C8 C1 E9 ?? 33 C1 …
$op2hex{4D 0F AF CC 44 69 C2 [4] 4C 03 C9 45 8B D1 4D 0F AF D4 41 8D 0C 11 41 81 C0 [4] 02 C8 49 C1 E9 ?? 41 88 4B ?? 4D 03 D1 8B C8 45 8B CA C1 E1 ?? 33 C1}
$op3hex{33 C1 4C 0F AF C7 8B C8 C1 E1 ?? 4D 03 C2 33 C1}

Condition

2 of them

In plain words (Heuristic)

  • At least 2 patterns in the rule must match.

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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).

  • 851c2c99ebafd4e5e9e140cfe3f2d03533846ca16f8151ae8ee0e83c692884b7

Licence & attribution

Author: MalGamy (Nextron Systems)

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: d11170df-570c-510c-80ec-39048acd0fbd

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