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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_MAL_LUA_Hunting_SKIPJACK_1

Hunting rule looking for strings observed in SKIPJACK installation script.

APT / threat actorSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Mandiant
Date
2023-06-15
Modified
2023-12-05
Score / Quality
70 / 85

What this rule detects

Hunting rule looking for strings observed in SKIPJACK installation script.

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
apt-mal-lua-hunting-skipjack-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_APT_MAL_LUA_Hunting_SKIPJACK_1
{
	meta:
		description = "Hunting rule looking for strings observed in SKIPJACK installation script."
		author = "Mandiant"
		id = "0026375c-7f37-5ef9-bd55-5b9fc499e5d2"
		date = "2023-06-15"
		modified = "2023-12-05"
		reference = "https://www.mandiant.com/resources/blog/barracuda-esg-exploited-globally"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_barracuda_esg_unc4841_jun23.yar#L175-L193"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "e4e86c273a2b67a605f5d4686783e0cc"
		logic_hash = "8890cd9ab8190f12997e0653e43c89816df03c7bd41842e5ad21b1986819843e"
		score = 70
		quality = 85
		tags = ""

	strings:
		$str1 = "hdr:name() == 'Content-ID'" base64
		$str2 = "hdr:body() ~= nil" base64
		$str3 = "string.match(hdr:body(),\"^[%w%+/=\\r\\n]+$\")" base64
		$str4 = "openssl aes-256-cbc" base64
		$str5 = "mod_content.lua"
		$str6 = "#!/bin/sh"

	condition:
		all of them
}

Strings (6 patterns)

IdentifierTypeValueModifiers
$str1text"hdr:name() == 'Content-ID'"base64
$str2text"hdr:body() ~= nil"base64
$str3text"string.match(hdr:body(),\"^[%w%+/=\\r\\n]+$\")"base64
$str4text"openssl aes-256-cbc"base64
$str5text"mod_content.lua"
$str6text"#!/bin/sh"

Condition

all of them

In plain words (Heuristic)

  • 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).

  • e4e86c273a2b67a605f5d4686783e0cc

Licence & attribution

Author: Mandiant

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: 0026375c-7f37-5ef9-bd55-5b9fc499e5d2

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