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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_MAL_3Cxdesktopapp_Macos_Backdoor_Mar23

Detects 3CXDesktopApp MacOS Backdoor component

MalwareSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
X__Junior (Nextron Systems)
Date
2023-03-30
Modified
2023-12-05
Score / Quality
80 / 85

What this rule detects

Detects 3CXDesktopApp MacOS Backdoor component

It defines 4 patterns (2 text, 2 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
mal-3cxdesktopapp-macos-backdoor-mar23.yarDetection Rule License 1.1
rule SIGNATURE_BASE_MAL_3Cxdesktopapp_Macos_Backdoor_Mar23 : FILE
{
	meta:
		description = "Detects 3CXDesktopApp MacOS Backdoor component"
		author = "X__Junior (Nextron Systems)"
		id = "80046c8e-0c2a-5885-b140-a6084f48160d"
		date = "2023-03-30"
		modified = "2023-12-05"
		reference = "https://www.volexity.com/blog/2023/03/30/3cx-supply-chain-compromise-leads-to-iconic-incident/"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/gen_mal_3cx_compromise_mar23.yar#L251-L275"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "a64fa9f1c76457ecc58402142a8728ce34ccba378c17318b3340083eeb7acc67"
		logic_hash = "777a0a29c376f3697021dd627e716c31bda7933c5f40a8fe79b80e3cea46ce43"
		score = 80
		quality = 85
		tags = "FILE"

	strings:
		$sa1 = "%s/.main_storage" ascii fullword
		$sa2 = "%s/UpdateAgent" ascii fullword
		$op1 = { 31 C0 41 80 34 06 ?? 48 FF C0 48 83 F8 ?? 75 ?? BE ?? ?? ?? ?? BA ?? ?? ?? ?? 4C 89 F7 48 89 D9 E8 ?? ?? ?? ?? 48 89 DF E8 ?? ?? ?? ?? 48 89 DF E8 ?? ?? ?? ?? 4C 89 F7 5B 41 5E 41 5F E9 ?? ?? ?? ?? 5B 41 5E 41 5F C3}
		$op2 = { 0F 11 84 24 ?? ?? ?? ?? 0F 28 05 ?? ?? ?? ?? 0F 29 84 24 ?? ?? ?? ?? 0F 28 05 ?? ?? ?? ?? 0F 29 84 24 ?? ?? ?? ?? 31 C0 80 B4 04 ?? ?? ?? ?? ?? 48 FF C0}

	condition:
		(( uint16( 0 ) == 0xfeca or uint16( 0 ) == 0xfacf or uint32( 0 ) == 0xbebafeca ) and filesize < 6MB and ( ( 1 of ( $sa* ) and 1 of ( $op* ) ) or all of ( $sa* ) ) ) or ( all of ( $op* ) )
}

Strings (4 patterns)

IdentifierTypeValueModifiers
$sa1text"%s/.main_storage"ascii fullword
$sa2text"%s/UpdateAgent"ascii fullword
$op1hex{ 31 C0 41 80 34 06 ?? 48 FF C0 48 83 F8 ?? 75 ?? BE ?? ?? ?? ?? BA ?? ?? ?? ?? 4C 89 F7 48 89 D9 E8 ?? ?? ?? ?? 48 89 DF E8 ?? ?? ?? ?? 48 89 DF E8 ?? ?? ?? ?? …
$op2hex{ 0F 11 84 24 ?? ?? ?? ?? 0F 28 05 ?? ?? ?? ?? 0F 29 84 24 ?? ?? ?? ?? 0F 28 05 ?? ?? ?? ?? 0F 29 84 24 ?? ?? ?? ?? 31 C0 80 B4 04 ?? ?? ?? ?? ?? 48 FF C0}

Condition

(( uint16( 0 ) == 0xfeca or uint16( 0 ) == 0xfacf or uint32( 0 ) == 0xbebafeca ) and filesize < 6MB and ( ( 1 of ( $sa* ) and 1 of ( $op* ) ) or all of ( $sa* ) ) ) or ( all of ( $op* ) )

In plain words (Heuristic)

  • The file must be smaller than 6MB (a cheap guard that skips large files).
  • All patterns in ( $sa* ) must match.
  • All patterns in ( $op* ) must match.
  • At least 1 patterns in ( $sa* ) must match.
  • At least 1 patterns in ( $op* ) 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).

  • a64fa9f1c76457ecc58402142a8728ce34ccba378c17318b3340083eeb7acc67

Licence & attribution

Author: 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: 80046c8e-0c2a-5885-b140-a6084f48160d

Tags:FILE

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