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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_MAL_G_Dropper_BRICKSTEAL_2

Detects backdoor BRICKSTEAL dropper used by APT group UNC5221 (China Nexus)

MalwareSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Google Threat Intelligence Group (GTIG) (modified by Florian Roth)
Date
2025-09-25
Modified
2026-05-15
Score / Quality
75 / 85

What this rule detects

Detects backdoor BRICKSTEAL dropper used by APT group UNC5221 (China Nexus)

It defines 6 patterns (6 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
mal-g-dropper-bricksteal-2.yarDetection Rule License 1.1
rule SIGNATURE_BASE_MAL_G_Dropper_BRICKSTEAL_2
{
	meta:
		description = "Detects backdoor BRICKSTEAL dropper used by APT group UNC5221 (China Nexus)"
		author = "Google Threat Intelligence Group (GTIG) (modified by Florian Roth)"
		id = "8139f8c0-4c18-51bd-bf23-8c4cdc3fd555"
		date = "2025-09-25"
		modified = "2026-05-15"
		reference = "https://cloud.google.com/blog/topics/threat-intelligence/brickstorm-espionage-campaign"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_cn_brickstorm_sep25.yar#L175-L193"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "e1bdcc59259b2bf476b873a9f94b9296efc7720d83fba04f6569217019ae3af8"
		score = 75
		quality = 85
		tags = ""

	strings:
		$str1_alt = "(Class<?>) method.invoke(" ascii wide
		$str2 = "(\"yv66vg" ascii wide
		$str3 = "request.getSession().getServletContext" ascii wide
		$str4 = ".getClass().getDeclaredField(" ascii wide
		$str5 = "new FilterDef();" ascii wide
		$str6 = "new FilterMap();" ascii wide

	condition:
		all of them
}

Strings (6 patterns)

IdentifierTypeValueModifiers
$str1_alttext"(Class<?>) method.invoke("ascii wide
$str2text"(\"yv66vg"ascii wide
$str3text"request.getSession().getServletContext"ascii wide
$str4text".getClass().getDeclaredField("ascii wide
$str5text"new FilterDef();"ascii wide
$str6text"new FilterMap();"ascii wide

Condition

all of them

In plain words (Heuristic)

  • All patterns in the rule must match.

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References

Licence & attribution

Author: Google Threat Intelligence Group (GTIG) (modified by Florian Roth)

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: 8139f8c0-4c18-51bd-bf23-8c4cdc3fd555

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