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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_MAL_ASPX_HAFNIUM_Chopper_Mar21_3

Detects HAFNIUM ASPX files dropped on compromised servers

APT / threat actorSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Florian Roth (Nextron Systems)
Date
2021-03-07
Modified
2023-12-05
Score / Quality
85 / 85

What this rule detects

Detects HAFNIUM ASPX files dropped on compromised servers

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
apt-mal-aspx-hafnium-chopper-mar21-3.yarDetection Rule License 1.1
rule SIGNATURE_BASE_APT_MAL_ASPX_HAFNIUM_Chopper_Mar21_3 : FILE
{
	meta:
		description = "Detects HAFNIUM ASPX files dropped on compromised servers"
		author = "Florian Roth (Nextron Systems)"
		id = "9c2ba123-63c4-5e9c-a08f-bd9db3304691"
		date = "2021-03-07"
		modified = "2023-12-05"
		reference = "https://www.microsoft.com/security/blog/2021/03/02/hafnium-targeting-exchange-servers/"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_hafnium.yar#L202-L216"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "391b366d78c2f24dc006a5365ec232a9a3c2fe0ea514b18897701ceeffcc81ca"
		score = 85
		quality = 85
		tags = "FILE"

	strings:
		$s1 = "runat=\"server\">void Page_Load(object" ascii wide
		$s2 = "Request.Files[0].SaveAs(Server.MapPath(" ascii wide

	condition:
		filesize < 50KB and all of them
}

Strings (2 patterns)

IdentifierTypeValueModifiers
$s1text"runat=\"server\">void Page_Load(object"ascii wide
$s2text"Request.Files[0].SaveAs(Server.MapPath("ascii wide

Condition

filesize < 50KB and all of them

In plain words (Heuristic)

  • The file must be smaller than 50KB (a cheap guard that skips large files).
  • All patterns in the rule must match.

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References

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: 9c2ba123-63c4-5e9c-a08f-bd9db3304691

Tags:FILE

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