YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_APT29_NOBELIUM_JS_Envyscout_May21_1

Detects EnvyScout deobfuscator code as used by NOBELIUM group

APT / threat actorSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X

Author: Florian Roth (Nextron Systems)
Date: 2021-05-29
Modified: 2025-03-21
Score / Quality: 75 / 85

What this rule detects

Detects EnvyScout deobfuscator code as used by NOBELIUM group

It defines 1 patterns (1 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar

apt-apt29-nobelium-js-envyscout-may21-1.yarDetection Rule License 1.1

rule SIGNATURE_BASE_APT_APT29_NOBELIUM_JS_Envyscout_May21_1 : FILE
{
	meta:
		description = "Detects EnvyScout deobfuscator code as used by NOBELIUM group"
		author = "Florian Roth (Nextron Systems)"
		id = "42739aad-a88a-545b-8256-1f727c79c4f8"
		date = "2021-05-29"
		modified = "2025-03-21"
		reference = "https://www.microsoft.com/security/blog/2021/05/28/breaking-down-nobeliums-latest-early-stage-toolset/"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_apt29_nobelium_may21.yar#L56-L67"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "ad8a7bb5a1d2065e3a573842fb37ee3c63b7695c18840f0c26d32e6ae3d99c6c"
		score = 75
		quality = 85
		tags = "FILE"

	strings:
		$x1 = "[i].charCodeAt(0) ^ 2);}"

	condition:
		filesize < 5000KB and 1 of them
}

Strings (1 patterns)

Identifier	Type	Value	Modifiers
$x1	text	"[i].charCodeAt(0) ^ 2);}"

Condition

filesize < 5000KB and 1 of them

In plain words (Heuristic)

The file must be smaller than 5000KB (a cheap guard that skips large files).
At least 1 patterns in the rule must match.

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.

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References

https://www.microsoft.com/security/blog/2021/05/28/breaking-down-nobeliums-latest-early-stage-toolset/

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: 42739aad-a88a-545b-8256-1f727c79c4f8

Tags:FILE

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