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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_SUSP_PS1_JAB_Pattern_Jun22_1

Detects suspicious UTF16 and Base64 encoded PowerShell code that starts with a $ sign and a single char variable

Suspicious / huntingSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Florian Roth (Nextron Systems)
Date
2022-06-10
Modified
2023-12-05
Score / Quality
70 / 85

What this rule detects

Detects suspicious UTF16 and Base64 encoded PowerShell code that starts with a $ sign and a single char variable

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
susp-ps1-jab-pattern-jun22-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_SUSP_PS1_JAB_Pattern_Jun22_1 : FILE
{
	meta:
		description = "Detects suspicious UTF16 and Base64 encoded PowerShell code that starts with a $ sign and a single char variable"
		author = "Florian Roth (Nextron Systems)"
		id = "9ecca7d9-3b63-5615-a223-5efa1c53510e"
		date = "2022-06-10"
		modified = "2023-12-05"
		reference = "Internal Research"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/gen_susp_ps_jab.yar#L2-L29"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "9ad61dca5c945ed87642668e3b834b12c813af244437903a5abb5c69459b9456"
		score = 70
		quality = 85
		tags = "FILE"

	strings:
		$xc1 = { 4a 41 42 ?? 41 43 41 41 50 51 41 67 41 }
		$xc2 = { 4a 00 41 00 42 00 ?? 00 41 00 43 00 41 00 41 00 50 00 51 00 41 00 67 00 41 }
		$xc3 = { 4a 41 42 ?? 41 44 30 41 }
		$xc4 = { 4a 00 41 00 42 00 ?? 00 41 00 44 00 30 00 41 }

	condition:
		filesize < 30MB and 1 of them
}

Strings (4 patterns)

IdentifierTypeValueModifiers
$xc1hex{ 4a 41 42 ?? 41 43 41 41 50 51 41 67 41 }
$xc2hex{ 4a 00 41 00 42 00 ?? 00 41 00 43 00 41 00 41 00 50 00 51 00 41 00 67 00 41 }
$xc3hex{ 4a 41 42 ?? 41 44 30 41 }
$xc4hex{ 4a 00 41 00 42 00 ?? 00 41 00 44 00 30 00 41 }

Condition

filesize < 30MB and 1 of them

In plain words (Heuristic)

  • The file must be smaller than 30MB (a cheap guard that skips large files).
  • At least 1 patterns in the rule must match.

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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: 9ecca7d9-3b63-5615-a223-5efa1c53510e

Tags:FILE

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