Skip to content
yararules.org
Menu

YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_UNC4736_NK_MAL_TAXHAUL_3CX_Apr23_1

Detects TAXHAUL (AKA TxRLoader) malware used in the 3CX compromise by UNC4736

APT / threat actorSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Mandiant
Date
2023-03-04
Modified
2023-12-05
Score / Quality
80 / 85

What this rule detects

Detects TAXHAUL (AKA TxRLoader) malware used in the 3CX compromise by UNC4736

Targets: Windows PE.

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
apt-unc4736-nk-mal-taxhaul-3cx-apr23-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_APT_UNC4736_NK_MAL_TAXHAUL_3CX_Apr23_1 : FILE
{
	meta:
		description = "Detects TAXHAUL (AKA TxRLoader) malware used in the 3CX compromise by UNC4736"
		author = "Mandiant"
		id = "25a80f98-03d6-59e6-84e6-6d847a6c591e"
		date = "2023-03-04"
		modified = "2023-12-05"
		reference = "https://www.3cx.com/blog/news/mandiant-initial-results/"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_mal_gopuram_apr23.yar#L77-L90"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "f67af611d0b3d96e4aaf7b3b5e49c1fb536e61a430b79ac0a0560ef3773ba140"
		score = 80
		quality = 85
		tags = "FILE"

	strings:
		$p00_0 = {410f45fe4c8d3d[4]eb??4533f64c8d3d[4]eb??4533f64c8d3d[4]eb}
		$p00_1 = {4d3926488b01400f94c6ff90[4]41b9[4]eb??8bde4885c074}

	condition:
		uint16( 0 ) == 0x5A4D and any of them
}

Strings (2 patterns)

IdentifierTypeValueModifiers
$p00_0hex{410f45fe4c8d3d[4]eb??4533f64c8d3d[4]eb??4533f64c8d3d[4]eb}
$p00_1hex{4d3926488b01400f94c6ff90[4]41b9[4]eb??8bde4885c074}

Condition

uint16( 0 ) == 0x5A4D and any of them

In plain words (Heuristic)

  • The file must start with “MZ” — a Windows executable (PE).
  • At least one pattern in the rule must match.

Test this rule in your browser

Drop a file to scan it with this rule using YARA-X compiled to WebAssembly. Nothing is uploaded.

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

Open in editor

References

Licence & attribution

Author: Mandiant

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: 25a80f98-03d6-59e6-84e6-6d847a6c591e

Tags:FILE

Related rules