YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_SUSP_NK_3CX_RC4_Key_Mar23_1

Detects RC4 key used in 3CX binaries known to be malicious

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

Author: Florian Roth (Nextron Systems)
Date: 2023-03-29
Modified: 2023-12-05
Score / Quality: 70 / 85

What this rule detects

Detects RC4 key used in 3CX binaries known to be malicious

Targets: Windows PE.

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar

apt-susp-nk-3cx-rc4-key-mar23-1.yarDetection Rule License 1.1

rule SIGNATURE_BASE_APT_SUSP_NK_3CX_RC4_Key_Mar23_1 : FILE
{
	meta:
		description = "Detects RC4 key used in 3CX binaries known to be malicious"
		author = "Florian Roth (Nextron Systems)"
		id = "18ea2185-11a1-51ad-a51a-df9e6357bb58"
		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#L100-L117"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "7986bbaee8940da11ce089383521ab420c443ab7b15ed42aed91fd31ce833896"
		hash = "59e1edf4d82fae4978e97512b0331b7eb21dd4b838b850ba46794d9c7a2c0983"
		hash = "aa124a4b4df12b34e74ee7f6c683b2ebec4ce9a8edcf9be345823b4fdcf5d868"
		hash = "c485674ee63ec8d4e8fde9800788175a8b02d3f9416d0e763360fff7f8eb4e02"
		logic_hash = "8324b537b149ad3816b12ae0f887f66a284a8e1ef4fe7cf51eb21d59c0f055b9"
		score = 70
		quality = 85
		tags = "FILE"

	strings:
		$x1 = "3jB(2bsG#@c7"

	condition:
		( uint16( 0 ) == 0xcfd0 or uint16( 0 ) == 0x5a4d ) and $x1
}

Strings (1 patterns)

Identifier	Type	Value	Modifiers
$x1	text	"3jB(2bsG#@c7"

Condition

( uint16( 0 ) == 0xcfd0 or uint16( 0 ) == 0x5a4d ) and $x1

In plain words (Heuristic)

The file must start with “MZ” — a Windows executable (PE).
Pattern $x1 must be present.

Test this rule in your browser

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Drop a file here or click to chooseScanned locally with YARA-X. Files up to 200 MB.

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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).

7986bbaee8940da11ce089383521ab420c443ab7b15ed42aed91fd31ce833896
59e1edf4d82fae4978e97512b0331b7eb21dd4b838b850ba46794d9c7a2c0983
aa124a4b4df12b34e74ee7f6c683b2ebec4ce9a8edcf9be345823b4fdcf5d868
c485674ee63ec8d4e8fde9800788175a8b02d3f9416d0e763360fff7f8eb4e02

Licence & attribution

Author: Florian Roth (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: 18ea2185-11a1-51ad-a51a-df9e6357bb58

Tags:FILE

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