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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_MAL_G_Backdoor_BRICKSTEAL_1

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

It defines 5 patterns (5 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
mal-g-backdoor-bricksteal-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_MAL_G_Backdoor_BRICKSTEAL_1 : FILE
{
	meta:
		description = "Detects backdoor BRICKSTEAL used by APT group UNC5221 (China Nexus)"
		author = "Google Threat Intelligence Group (GTIG) (modified by Florian Roth)"
		id = "2457d600-d9dd-504f-baa3-699ec5c61eae"
		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#L137-L153"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "27413b63eae84d95cf0ca920e9ac1daba200281ecc32cc9922c0e7850c7f0571"
		score = 75
		quality = 85
		tags = "FILE"

	strings:
		$str1 = "comvmware"
		$str2 = "abcdABCD1234!@#$"
		$str3 = "ads.png"
		$str4 = "User-Agent"
		$str5 = "com/vmware/"

	condition:
		all of them and filesize < 10KB
}

Strings (5 patterns)

IdentifierTypeValueModifiers
$str1text"comvmware"
$str2text"abcdABCD1234!@#$"
$str3text"ads.png"
$str4text"User-Agent"
$str5text"com/vmware/"

Condition

all of them and filesize < 10KB

In plain words (Heuristic)

  • The file must be smaller than 10KB (a cheap guard that skips large files).
  • 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: 2457d600-d9dd-504f-baa3-699ec5c61eae

Tags:FILE

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