YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_SUSP_3CX_App_Signed_Binary_Mar23_1

Detects 3CX application binaries signed with a certificate and created in a time frame in which other known malicious binaries have been created

Suspicious / huntingSignature 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: 65 / 85

What this rule detects

Detects 3CX application binaries signed with a certificate and created in a time frame in which other known malicious binaries have been created

Targets: Windows PE.

It defines 3 patterns (2 text, 1 hex, 0 regex). YARA modules used: pe.

Summary generated from the rule's metadata and condition.

Rule source

Download .yar

Includes the imports needed to compile it on its own.

susp-3cx-app-signed-binary-mar23-1.yarDetection Rule License 1.1

import "pe"

rule SIGNATURE_BASE_SUSP_3CX_App_Signed_Binary_Mar23_1 : FILE
{
	meta:
		description = "Detects 3CX application binaries signed with a certificate and created in a time frame in which other known malicious binaries have been created"
		author = "Florian Roth (Nextron Systems)"
		id = "b6ce4c1d-1b7b-5e0c-af4c-05cb3ad0a4e0"
		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#L119-L139"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "fad482ded2e25ce9e1dd3d3ecc3227af714bdfbbde04347dbc1b21d6a3670405"
		hash = "dde03348075512796241389dfea5560c20a3d2a2eac95c894e7bbed5e85a0acc"
		logic_hash = "3834b5ebb5a0db27a452fda1c97c921b2c9c8702505738232b15a3ed4a47dc47"
		score = 65
		quality = 85
		tags = "FILE"

	strings:
		$sa1 = "3CX Ltd1"
		$sa2 = "3CX Desktop App" wide
		$sc1 = { 1B 66 11 DF 9C 9A 4D 6E CC 8E D5 0C 9B 91 78 73 }

	condition:
		uint16( 0 ) == 0x5a4d and pe.timestamp > 1669680000 and pe.timestamp < 1680108505 and all of ( $sa* ) and $sc1
}

Strings (3 patterns)

Identifier	Type	Value	Modifiers
$sa1	text	"3CX Ltd1"
$sa2	text	"3CX Desktop App"	wide
$sc1	hex	{ 1B 66 11 DF 9C 9A 4D 6E CC 8E D5 0C 9B 91 78 73 }

Condition

uint16( 0 ) == 0x5a4d and pe.timestamp > 1669680000 and pe.timestamp < 1680108505 and all of ( $sa* ) and $sc1

In plain words (Heuristic)

The file must start with “MZ” — a Windows executable (PE).
All patterns in ( $sa* ) must match.
Uses the pe module.
Pattern $sc1 must be present.

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

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).

fad482ded2e25ce9e1dd3d3ecc3227af714bdfbbde04347dbc1b21d6a3670405
dde03348075512796241389dfea5560c20a3d2a2eac95c894e7bbed5e85a0acc

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: b6ce4c1d-1b7b-5e0c-af4c-05cb3ad0a4e0

Tags:FILE

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