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SEKOIA_Tinyfluff_Nodejs

Detect TinyFluff backdoor by OldGremlin

MalwareTinyfluffSEKOIA.IO CommunityDetection Rule License 1.1Compiles with YARA-X
Author
Sekoia.io
Date
2022-04-20
Modified
2024-12-19
Score / Quality
75 / 80

What this rule detects

Detect TinyFluff backdoor by OldGremlin

Associated malware family: Tinyfluff.

Targets: Windows PE.

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
tinyfluff-nodejs.yarDetection Rule License 1.1
rule SEKOIA_Tinyfluff_Nodejs : FILE
{
	meta:
		description = "Detect TinyFluff backdoor by OldGremlin"
		author = "Sekoia.io"
		id = "ca8cbd90-f275-4442-8354-b8b069e2efc3"
		date = "2022-04-20"
		modified = "2024-12-19"
		reference = "https://blog.group-ib.com/oldgremlin_comeback"
		source_url = "https://github.com/SEKOIA-IO/Community/blob/a438a5901a211c2abdf75da9c93921ef187473d1/yara_rules/tinyfluff_nodejs.yar#L1-L21"
		license_url = "https://github.com/SEKOIA-IO/Community/blob/a438a5901a211c2abdf75da9c93921ef187473d1/LICENSE.md"
		hash = "bd0a6a3628f268a37ac9d708d03f57feef5ed55e"
		hash = "bd0a6a3628f268a37ac9d708d03f57feef5ed55e"
		logic_hash = "7fa07b6ea32b914887bdcada0f9fda086bc29a44bfdf27e7433ef589192f4b82"
		score = 75
		quality = 80
		tags = "FILE"
		version = "1.0"
		classification = "TLP:CLEAR"

	strings:
		$s1 = "TinyFluff.pdb" fullword ascii
		$s2 = "node.exe" fullword wide

	condition:
		filesize < 500KB and uint16be( 0 ) == 0x4d5a and all of them
}

Strings (2 patterns)

IdentifierTypeValueModifiers
$s1text"TinyFluff.pdb"fullword ascii
$s2text"node.exe"fullword wide

Condition

filesize < 500KB and uint16be( 0 ) == 0x4d5a and all of them

In plain words (Heuristic)

  • The file must start with “MZ” — a Windows executable (PE).
  • The file must be smaller than 500KB (a cheap guard that skips large files).
  • All patterns in the rule must match.

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References

Sample hashes

Hashes of samples the author lists in the rule's meta (look them up in your threat-intelligence platform).

  • bd0a6a3628f268a37ac9d708d03f57feef5ed55e

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: ca8cbd90-f275-4442-8354-b8b069e2efc3

Metadata

version1.0
classificationTLP:CLEAR

Tags:FILE

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