YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_MAL_NK_3CX_ICONIC_Stealer_Mar23_1

Detects ICONIC stealer payload used in the 3CX incident

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

Author: Florian Roth (Nextron Systems)
Date: 2023-03-31
Modified: 2023-12-05
Score / Quality: 80 / 85

What this rule detects

Detects ICONIC stealer payload used in the 3CX incident

Associated malware family: Iconic Stealer.

Targets: Windows PE.

It defines 8 patterns (6 text, 2 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar

apt-mal-nk-3cx-iconic-stealer-mar23-1.yarDetection Rule License 1.1

rule SIGNATURE_BASE_APT_MAL_NK_3CX_ICONIC_Stealer_Mar23_1 : FILE
{
	meta:
		description = "Detects ICONIC stealer payload used in the 3CX incident"
		author = "Florian Roth (Nextron Systems)"
		id = "e92b5b90-1146-5235-9711-a4d42689c49b"
		date = "2023-03-31"
		modified = "2023-12-05"
		reference = "https://github.com/volexity/threat-intel/blob/main/2023/2023-03-30%203CX/attachments/iconicstealer.7z"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/gen_mal_3cx_compromise_mar23.yar#L279-L304"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "8ab3a5eaaf8c296080fadf56b265194681d7da5da7c02562953a4cb60e147423"
		logic_hash = "1f57a2af4a5b9e71e2b72ddc3839400731d9d37eb4349c393b37b3f86c0c7f73"
		score = 80
		quality = 85
		tags = "FILE"

	strings:
		$s1 = "{\"HostName\": \"%s\", \"DomainName\": \"%s\", \"OsVersion\": \"%d.%d.%d\"}" wide fullword
		$s2 = "******************************** %s ******************************" wide fullword
		$s3 = "AppData\\Local\\BraveSoftware\\Brave-Browser\\User Data" wide fullword
		$s4 = "AppData\\Roaming\\Mozilla\\Firefox\\Profiles" wide fullword
		$s5 = "SELECT url, title FROM urls ORDER BY id DESC LIMIT 500" wide fullword
		$s6 = "TEXT value in %s.%s" ascii fullword
		$op1 = { 48 63 d1 48 63 ce 49 03 d1 49 03 cd 4c 63 c7 e8 87 1f 09 00 8b 45 d0 44 8d 04 37 }
		$op2 = { 48 8b c8 8b 56 f0 48 89 46 d8 e8 78 8f f8 ff e9 ec 13 00 00 c7 46 20 ff ff ff ff e9 e0 13 00 00 33 ff }

	condition:
		uint16( 0 ) == 0x5a4d and filesize < 4000KB and 4 of them or 6 of them
}

Strings (8 patterns)

Identifier	Type	Value	Modifiers
$s1	text	"{\"HostName\": \"%s\", \"DomainName\": \"%s\", \"OsVersion\": \"%d.%d.%d\"}"	wide fullword
$s2	text	"****************************** %s ****************************"	wide fullword
$s3	text	"AppData\\Local\\BraveSoftware\\Brave-Browser\\User Data"	wide fullword
$s4	text	"AppData\\Roaming\\Mozilla\\Firefox\\Profiles"	wide fullword
$s5	text	"SELECT url, title FROM urls ORDER BY id DESC LIMIT 500"	wide fullword
$s6	text	"TEXT value in %s.%s"	ascii fullword
$op1	hex	{ 48 63 d1 48 63 ce 49 03 d1 49 03 cd 4c 63 c7 e8 87 1f 09 00 8b 45 d0 44 8d 04 37 }
$op2	hex	{ 48 8b c8 8b 56 f0 48 89 46 d8 e8 78 8f f8 ff e9 ec 13 00 00 c7 46 20 ff ff ff ff e9 e0 13 00 00 33 ff }

Condition

uint16( 0 ) == 0x5a4d and filesize < 4000KB and 4 of them or 6 of them

In plain words (Heuristic)

The file must start with “MZ” — a Windows executable (PE).
The file must be smaller than 4000KB (a cheap guard that skips large files).
At least 4 patterns in the rule must match.
At least 6 patterns in the rule must match.

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References

https://github.com/volexity/threat-intel/blob/main/2023/2023-03-30%203CX/attachments/iconicstealer.7z

Sample hashes

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

8ab3a5eaaf8c296080fadf56b265194681d7da5da7c02562953a4cb60e147423

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: e92b5b90-1146-5235-9711-a4d42689c49b

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