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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_MAL_G_APT_Backdoor_BRICKSTORM_1

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

Targets: Linux ELF.

It defines 14 patterns (14 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
mal-g-apt-backdoor-brickstorm-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_MAL_G_APT_Backdoor_BRICKSTORM_1 : FILE
{
	meta:
		description = "Detects BRICKSTORM backdoor used by APT group UNC5221 (China Nexus)"
		author = "Google Threat Intelligence Group (GTIG) (modified by Florian Roth)"
		id = "0e56b78c-121d-5ee5-ad3a-103088ecafeb"
		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#L55-L81"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "4645f2f6800bc654d5fa812237896b00"
		logic_hash = "ffaeca48c96445044844779f28c46a5c6029ba96191d3faafbc8f3864c29e21b"
		score = 75
		quality = 85
		tags = "FILE"

	strings:
		$ = "WRITE_LOGWednesday"
		$ = "/home/vsphere-ui/"
		$ = "WRITE_LOG=true"
		$ = "dns rcode: %v"
		$ = "/libs/doh.createDnsMessage"
		$ = "/libs/func1.(*Client).BackgroundRun"
		$ = "/libs/func1.CreateClient"
		$ = "/core/extends/command.CommandNoContext"
		$ = "/core/extends/command.ExecuteCmd"
		$ = "/core/extends/command.RunShell"
		$ = "/libs/fs.(*RemoteDriver).DeleteFile"
		$ = "/libs/fs.(*RemoteDriver).GetFile"
		$ = "/libs/fs.(*RemoteDriver).PutFile"
		$ = "/libs/doh/doh.go"

	condition:
		uint32( 0 ) == 0x464c457f and 5 of them
}

Strings (14 patterns)

IdentifierTypeValueModifiers
$text"WRITE_LOGWednesday"
$text"/home/vsphere-ui/"
$text"WRITE_LOG=true"
$text"dns rcode: %v"
$text"/libs/doh.createDnsMessage"
$text"/libs/func1.(*Client).BackgroundRun"
$text"/libs/func1.CreateClient"
$text"/core/extends/command.CommandNoContext"
$text"/core/extends/command.ExecuteCmd"
$text"/core/extends/command.RunShell"
$text"/libs/fs.(*RemoteDriver).DeleteFile"
$text"/libs/fs.(*RemoteDriver).GetFile"
$text"/libs/fs.(*RemoteDriver).PutFile"
$text"/libs/doh/doh.go"

Condition

uint32( 0 ) == 0x464c457f and 5 of them

In plain words (Heuristic)

  • The file must start with the ELF header — a Linux/Unix executable.
  • At least 5 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).

  • 4645f2f6800bc654d5fa812237896b00

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: 0e56b78c-121d-5ee5-ad3a-103088ecafeb

Tags:FILE

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