YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_MAL_NK_3CX_Malicious_Samples_Mar23_3

Detects malicious DLLs related to 3CX compromise (decrypted payload)

APT / threat actorSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X

Author: Florian Roth , X__Junior (Nextron Systems)
Date: 2023-03-29
Modified: 2023-12-05
Score / Quality: 80 / 85

What this rule detects

Detects malicious DLLs related to 3CX compromise (decrypted payload)

It defines 6 patterns (0 text, 6 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar

apt-mal-nk-3cx-malicious-samples-mar23-3.yarDetection Rule License 1.1

rule SIGNATURE_BASE_APT_MAL_NK_3CX_Malicious_Samples_Mar23_3
{
	meta:
		description = "Detects malicious DLLs related to 3CX compromise (decrypted payload)"
		author = "Florian Roth , X__Junior (Nextron Systems)"
		id = "d2d361b6-8485-57eb-b6eb-88785f42e93e"
		date = "2023-03-29"
		modified = "2023-12-05"
		reference = "https://www.reddit.com/r/crowdstrike/comments/125r3uu/20230329_situational_awareness_crowdstrike/"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/gen_mal_3cx_compromise_mar23.yar#L56-L79"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "aa4e398b3bd8645016d8090ffc77d15f926a8e69258642191deb4e68688ff973"
		logic_hash = "adfe04904d796690631e5841ee1ee10c767f9f4c340e5b9df78918e981359d4d"
		score = 80
		quality = 85
		tags = ""

	strings:
		$opa1 = { 41 81 C0 ?? ?? ?? ?? 02 C8 49 C1 E9 ?? 41 88 4B ?? 4D 03 D1 8B C8 45 8B CA C1 E1 ?? 33 C1 41 69 D0 ?? ?? ?? ?? 8B C8 C1 E9 ?? 33 C1 8B C8 C1 E1 ?? 81 C2 ?? ?? ?? ?? 33 C1 43 8D 0C 02 02 C8 49 C1 EA ?? 41 88 0B 8B C8 C1 E1 ?? 33 C1 44 69 C2 ?? ?? ?? ?? 8B C8 C1 E9 ?? 33 C1 8B C8 C1 E1 ?? 41 81 C0 }
		$opa2 = { 8B C8 41 69 D1 ?? ?? ?? ?? C1 E1 ?? 33 C1 45 8B CA 8B C8 C1 E9 ?? 33 C1 81 C2 ?? ?? ?? ?? 8B C8 C1 E1 ?? 33 C1 41 8B C8 4C 0F AF CF 44 69 C2 ?? ?? ?? ?? 4C 03 C9 45 8B D1 4C 0F AF D7}
		$opb1 = { 45 33 C9 48 89 6C 24 ?? 48 8D 44 24 ?? 48 89 6C 24 ?? 8B D3 48 89 B4 24 ?? ?? ?? ?? 48 89 44 24 ?? 45 8D 41 ?? FF 15 }
		$opb2 = { 44 8B 0F 45 8B C6 48 8B 4D ?? 49 8B D7 44 89 64 24 ?? 48 89 7C 24 ?? 44 89 4C 24 ?? 4C 8D 4D ?? 48 89 44 24 ?? 44 89 64 24 ?? 4C 89 64 24 ?? FF 15}
		$opb3 = { 48 FF C2 66 44 39 2C 56 75 ?? 4C 8D 4C 24 ?? 45 33 C0 48 8B CE FF 15 ?? ?? ?? ?? 85 C0 0F 84 ?? ?? ?? ?? 44 0F B7 44 24 ?? 33 F6 48 8B 54 24 ?? 45 33 C9 48 8B 0B 48 89 74 24 ?? 89 74 24 ?? C7 44 24 ?? ?? ?? ?? ?? 48 89 74 24 ?? FF 15 }
		$opb4 = { 33 C0 48 8D 6B ?? 4C 8D 4C 24 ?? 89 44 24 ?? BA ?? ?? ?? ?? 48 89 44 24 ?? 48 8B CD 89 44 24 ?? 44 8D 40 ?? 8B F8 FF 15}

	condition:
		( all of ( $opa* ) ) or ( 1 of ( $opa* ) and 1 of ( $opb* ) ) or ( 3 of ( $opb* ) )
}

Strings (6 patterns)

Identifier	Type	Value
$opa1	hex	{ 41 81 C0 ?? ?? ?? ?? 02 C8 49 C1 E9 ?? 41 88 4B ?? 4D 03 D1 8B C8 45 8B CA C1 E1 ?? 33 C1 41 69 D0 ?? ?? ?? ?? 8B C8 C1 E9 ?? 33 C1 8B C8 C1 E1 ?? 81 C2 ?? ?? …
$opa2	hex	{ 8B C8 41 69 D1 ?? ?? ?? ?? C1 E1 ?? 33 C1 45 8B CA 8B C8 C1 E9 ?? 33 C1 81 C2 ?? ?? ?? ?? 8B C8 C1 E1 ?? 33 C1 41 8B C8 4C 0F AF CF 44 69 C2 ?? ?? ?? ?? 4C 03 …
$opb1	hex	{ 45 33 C9 48 89 6C 24 ?? 48 8D 44 24 ?? 48 89 6C 24 ?? 8B D3 48 89 B4 24 ?? ?? ?? ?? 48 89 44 24 ?? 45 8D 41 ?? FF 15 }
$opb2	hex	{ 44 8B 0F 45 8B C6 48 8B 4D ?? 49 8B D7 44 89 64 24 ?? 48 89 7C 24 ?? 44 89 4C 24 ?? 4C 8D 4D ?? 48 89 44 24 ?? 44 89 64 24 ?? 4C 89 64 24 ?? FF 15}
$opb3	hex	{ 48 FF C2 66 44 39 2C 56 75 ?? 4C 8D 4C 24 ?? 45 33 C0 48 8B CE FF 15 ?? ?? ?? ?? 85 C0 0F 84 ?? ?? ?? ?? 44 0F B7 44 24 ?? 33 F6 48 8B 54 24 ?? 45 33 C9 48 8B …
$opb4	hex	{ 33 C0 48 8D 6B ?? 4C 8D 4C 24 ?? 89 44 24 ?? BA ?? ?? ?? ?? 48 89 44 24 ?? 48 8B CD 89 44 24 ?? 44 8D 40 ?? 8B F8 FF 15}

Condition

( all of ( $opa* ) ) or ( 1 of ( $opa* ) and 1 of ( $opb* ) ) or ( 3 of ( $opb* ) )

In plain words (Heuristic)

All patterns in ( $opa* ) must match.
At least 1 patterns in ( $opa* ) must match.
At least 1 patterns in ( $opb* ) must match.
At least 3 patterns in ( $opb* ) must match.

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References

https://www.reddit.com/r/crowdstrike/comments/125r3uu/20230329_situational_awareness_crowdstrike/

Sample hashes

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

aa4e398b3bd8645016d8090ffc77d15f926a8e69258642191deb4e68688ff973

Licence & attribution

Author: Florian Roth , X__Junior (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: d2d361b6-8485-57eb-b6eb-88785f42e93e