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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_WEBSHELL_ASPX_Chopper_Like_Mar21_1

Detects Chopper like ASPX Webshells

WebshellSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Florian Roth (Nextron Systems)
Date
2021-03-31
Modified
2023-12-05
Score / Quality
85 / 85

What this rule detects

Detects Chopper like ASPX Webshells

It defines 4 patterns (4 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
webshell-aspx-chopper-like-mar21-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_WEBSHELL_ASPX_Chopper_Like_Mar21_1 : FILE
{
	meta:
		description = "Detects Chopper like ASPX Webshells"
		author = "Florian Roth (Nextron Systems)"
		id = "a4dc1880-865f-5e20-89a2-3a642c453ef9"
		date = "2021-03-31"
		modified = "2023-12-05"
		reference = "Internal Research"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_hafnium.yar#L399-L416"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "ac44513e5ef93d8cbc17219350682c2246af6d5eb85c1b4302141d94c3b06c90"
		logic_hash = "baa9eb1e3c4ac5ce49d27b1c3f75c8b6590567e25d98761a8b704478f2cee970"
		score = 85
		quality = 85
		tags = "FILE"

	strings:
		$s1 = "http://f/<script language=\"JScript\" runat=\"server\">var _0x" ascii
		$s2 = "));function Page_Load(){var _0x" ascii
		$s3 = ";eval(Request[_0x" ascii
		$s4 = "','orange','unsafe','" ascii

	condition:
		filesize < 3KB and 1 of them or 2 of them
}

Strings (4 patterns)

IdentifierTypeValueModifiers
$s1text"http://f/<script language=\"JScript\" runat=\"server\">var _0x"ascii
$s2text"));function Page_Load(){var _0x"ascii
$s3text";eval(Request[_0x"ascii
$s4text"','orange','unsafe','"ascii

Condition

filesize < 3KB and 1 of them or 2 of them

In plain words (Heuristic)

  • The file must be smaller than 3KB (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.

Test this rule in your browser

Drop a file to scan it with this rule using YARA-X compiled to WebAssembly. Nothing is uploaded.

Drop a file here or click to chooseScanned locally with YARA-X. Files up to 200 MB.

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Sample hashes

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

  • ac44513e5ef93d8cbc17219350682c2246af6d5eb85c1b4302141d94c3b06c90

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: a4dc1880-865f-5e20-89a2-3a642c453ef9

Tags:FILE

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