YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_WEBSHELL_HAFNIUM_Secchecker_Mar21_1

Detects HAFNIUM SecChecker webshell

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

Author: Florian Roth (Nextron Systems)
Date: 2021-03-05
Modified: 2023-12-05
Score / Quality: 75 / 85

What this rule detects

Detects HAFNIUM SecChecker webshell

It defines 2 patterns (2 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar

apt-webshell-hafnium-secchecker-mar21-1.yarDetection Rule License 1.1

rule SIGNATURE_BASE_APT_WEBSHELL_HAFNIUM_Secchecker_Mar21_1 : FILE
{
	meta:
		description = "Detects HAFNIUM SecChecker webshell"
		author = "Florian Roth (Nextron Systems)"
		id = "73db3d78-7ece-53be-9efb-d19801993d5e"
		date = "2021-03-05"
		modified = "2023-12-05"
		reference = "https://twitter.com/markus_neis/status/1367794681237667840"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_hafnium.yar#L18-L33"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "b75f163ca9b9240bf4b37ad92bc7556b40a17e27c2b8ed5c8991385fe07d17d0"
		logic_hash = "e0e4df860bdde7d5c277f596535c493d926095be6f46f6ba41b6177afbfc5cd9"
		score = 75
		quality = 85
		tags = "FILE"

	strings:
		$x1 = "<%if(System.IO.File.Exists(\"c:\\\\program files (x86)\\\\fireeye\\\\xagt.exe" ascii
		$x2 = "\\csfalconservice.exe\")){Response.Write( \"3\");}%></head>" ascii fullword

	condition:
		uint16( 0 ) == 0x253c and filesize < 1KB and 1 of them or 2 of them
}

Strings (2 patterns)

Identifier	Type	Value	Modifiers
$x1	text	"<%if(System.IO.File.Exists(\"c:\\\\program files (x86)\\\\fireeye\\\\xagt.exe"	ascii
$x2	text	"\\csfalconservice.exe\")){Response.Write( \"3\");}%></head>"	ascii fullword

Condition

uint16( 0 ) == 0x253c and filesize < 1KB and 1 of them or 2 of them

In plain words (Heuristic)

The file must be smaller than 1KB (a cheap guard that skips large files).
At least 1 patterns in the rule must match.
At least 2 patterns in the rule must match.

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References

https://twitter.com/markus_neis/status/1367794681237667840

Sample hashes

Hashes of samples the author lists in the rule's meta (look them up in your threat-intelligence platform).

b75f163ca9b9240bf4b37ad92bc7556b40a17e27c2b8ed5c8991385fe07d17d0

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: 73db3d78-7ece-53be-9efb-d19801993d5e

Tags:FILE

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