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SEKOIA_Infostealer_Win_Acrstealer_Str

Finds ACR Stealer standalone samples based on specific strings.

MalwareAcr StealerSEKOIA.IO CommunityDetection Rule License 1.1Compiles with YARA-X
Author
Sekoia.io
Date
2024-04-22
Modified
2024-12-19
Score / Quality
75 / 80

What this rule detects

Finds ACR Stealer standalone samples based on specific strings.

Associated malware family: Acr Stealer.

Targets: Windows PE.

It defines 15 patterns (15 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

infostealer-win-acrstealer-str.yarDetection Rule License 1.1
rule SEKOIA_Infostealer_Win_Acrstealer_Str : FILE
{
	meta:
		description = "Finds ACR Stealer standalone samples based on specific strings."
		author = "Sekoia.io"
		id = "63b4d6ff-0cab-44ec-9d53-bb2612371a48"
		date = "2024-04-22"
		modified = "2024-12-19"
		reference = "https://github.com/SEKOIA-IO/Community"
		source_url = "https://github.com/SEKOIA-IO/Community/blob/a438a5901a211c2abdf75da9c93921ef187473d1/yara_rules/infostealer_win_acrstealer_str.yar#L1-L29"
		license_url = "https://github.com/SEKOIA-IO/Community/blob/a438a5901a211c2abdf75da9c93921ef187473d1/LICENSE.md"
		logic_hash = "53d313857577b39b51a3e396c078d39a8b8ab803295b689357c3e8ea94cac9f7"
		score = 75
		quality = 80
		tags = "FILE"
		version = "1.0"
		classification = "TLP:CLEAR"

	strings:
		$str01 = "ref.txt" ascii
		$str02 = "Wininet.dll" ascii
		$str03 = "Content-Type: application/octet-stream; boundary=----" ascii
		$str04 = "POST" ascii
		$str05 = "os_c" ascii fullword
		$str06 = "en_k" ascii fullword
		$str07 = "MyApp/1.0" ascii
		$str08 = "/Up/b" ascii
		$str09 = "Hello, World!" ascii
		$str10 = "/ujs/" ascii
		$str11 = "/Up/" ascii fullword
		$str12 = "ostr" ascii fullword
		$str13 = "brCH" ascii fullword
		$str14 = "brGk" ascii fullword
		$str15 = "https://steamcommunity.com/profiles/" ascii

	condition:
		uint16( 0 ) == 0x5A4D and 10 of them
}

Strings (15 patterns)

IdentifierTypeValueModifiers
$str01text"ref.txt"ascii
$str02text"Wininet.dll"ascii
$str03text"Content-Type: application/octet-stream; boundary=----"ascii
$str04text"POST"ascii
$str05text"os_c"ascii fullword
$str06text"en_k"ascii fullword
$str07text"MyApp/1.0"ascii
$str08text"/Up/b"ascii
$str09text"Hello, World!"ascii
$str10text"/ujs/"ascii
$str11text"/Up/"ascii fullword
$str12text"ostr"ascii fullword
$str13text"brCH"ascii fullword
$str14text"brGk"ascii fullword
$str15text"https://steamcommunity.com/profiles/"ascii

Condition

uint16( 0 ) == 0x5A4D and 10 of them

In plain words (Heuristic)

  • The file must start with “MZ” — a Windows executable (PE).
  • At least 10 patterns in the rule must match.

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References

Licence & attribution

Author: Sekoia.io

Source repository: SEKOIA.IO Community @ a438a5901a

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: 63b4d6ff-0cab-44ec-9d53-bb2612371a48

Metadata

version1.0
classificationTLP:CLEAR

Tags:FILE