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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_WEBSHELL_ASP_Embedded_Mar21_1

Detects ASP webshells

WebshellSignature 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
85 / 85

What this rule detects

Detects ASP webshells

It defines 3 patterns (3 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
webshell-asp-embedded-mar21-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_WEBSHELL_ASP_Embedded_Mar21_1 : FILE
{
	meta:
		description = "Detects ASP webshells"
		author = "Florian Roth (Nextron Systems)"
		id = "7cf7db9d-8f8a-51db-a0e6-84748e8f9e1f"
		date = "2021-03-05"
		modified = "2023-12-05"
		reference = "Internal Research"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_hafnium.yar#L2-L16"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "4a8b4cea6f53dad9771cb694ec55f305f04dfdbd8e663154cad672ca414c138c"
		score = 85
		quality = 85
		tags = "FILE"

	strings:
		$s1 = "<script runat=\"server\">" nocase
		$s2 = "new System.IO.StreamWriter(Request.Form["
		$s3 = ".Write(Request.Form["

	condition:
		filesize < 100KB and all of them
}

Strings (3 patterns)

IdentifierTypeValueModifiers
$s1text"<script runat=\"server\">"nocase
$s2text"new System.IO.StreamWriter(Request.Form["
$s3text".Write(Request.Form["

Condition

filesize < 100KB and all of them

In plain words (Heuristic)

  • The file must be smaller than 100KB (a cheap guard that skips large files).
  • All patterns in the rule must match.

Test this rule in your browser

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

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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: 7cf7db9d-8f8a-51db-a0e6-84748e8f9e1f

Tags:FILE

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