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SEKOIA_Koi_Koiloader

Detects Koi Loader

MalwareKoiloaderSEKOIA.IO CommunityDetection Rule License 1.1Compiles with YARA-X
Author
Sekoia.io
Date
2024-03-20
Modified
2024-12-19
Score / Quality
75 / 80

What this rule detects

Detects Koi Loader

Associated malware family: Koiloader.

Targets: Windows PE.

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
koi-koiloader.yarDetection Rule License 1.1
rule SEKOIA_Koi_Koiloader : FILE
{
	meta:
		description = "Detects Koi Loader"
		author = "Sekoia.io"
		id = "b8289d78-42de-4919-b2c5-3c926ddd8043"
		date = "2024-03-20"
		modified = "2024-12-19"
		reference = "https://github.com/SEKOIA-IO/Community"
		source_url = "https://github.com/SEKOIA-IO/Community/blob/a438a5901a211c2abdf75da9c93921ef187473d1/yara_rules/koi_koiloader.yar#L1-L19"
		license_url = "https://github.com/SEKOIA-IO/Community/blob/a438a5901a211c2abdf75da9c93921ef187473d1/LICENSE.md"
		logic_hash = "7b4f12b0dec3927a46db1c8b2163e54a0a515d2b7360ba94647097fecf3d4653"
		score = 75
		quality = 80
		tags = "FILE"
		version = "1.0"
		classification = "TLP:CLEAR"

	strings:
		$s2 = "%d|%s|%.16s|" ascii wide
		$s3 = "Release" ascii wide
		$s4 = "%s|%d.%d (%d)|%S|%S|%S" ascii wide
		$s5 = "InitiateSystemShutdownExW" ascii wide

	condition:
		uint16be( 0 ) == 0x4d5a and filesize < 11MB and all of them
}

Strings (4 patterns)

IdentifierTypeValueModifiers
$s2text"%d|%s|%.16s|"ascii wide
$s3text"Release"ascii wide
$s4text"%s|%d.%d (%d)|%S|%S|%S"ascii wide
$s5text"InitiateSystemShutdownExW"ascii wide

Condition

uint16be( 0 ) == 0x4d5a and filesize < 11MB and all of them

In plain words (Heuristic)

  • The file must start with “MZ” — a Windows executable (PE).
  • The file must be smaller than 11MB (a cheap guard that skips large files).
  • All 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: b8289d78-42de-4919-b2c5-3c926ddd8043

Metadata

version1.0
classificationTLP:CLEAR

Tags:FILE

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