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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_WEBSHELL_ASPX_Mar21_1

Detects ASPX Web Shells

WebshellSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Florian Roth (Nextron Systems)
Date
2021-03-12
Modified
2025-11-03
Score / Quality
75 / 85

What this rule detects

Detects ASPX Web Shells

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
webshell-aspx-mar21-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_WEBSHELL_ASPX_Mar21_1 : FILE
{
	meta:
		description = "Detects ASPX Web Shells"
		author = "Florian Roth (Nextron Systems)"
		id = "52884135-6b86-5e3e-a866-36a812d5a9af"
		date = "2021-03-12"
		modified = "2025-11-03"
		reference = "Internal Research"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/thor-webshells.yar#L9933-L9959"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "10b6e82125a2ddf3cc31a238e0d0c71a64f902e0d77171766713affede03174d"
		hash = "170bee832df176aac0a3c6c7d5aa3fee413b4572030a24c994a97e70f6648ffc"
		hash = "31c4d1fc81c052e269866deff324dffb215e7d481a47a2b6357a572a3e685d90"
		hash = "41b5c26ac194439612b68e9ec6a638eceaf00842c347ffa551eb009ef6c015a3"
		hash = "4b645bc773acde2b3cc204e77ac27c3f6991046c3b75f42d12bc90ec29cff9e3"
		hash = "602bb701b78895d4de32f5e78f3c511e5298ba244b29641b11a7c1c483789859"
		hash = "7ac47a17c511e25c06a53a1c7a5fbbf05f41f047a4a40b71afa81ce7b59f4b03"
		hash = "9a5097d0e8dc29a2814adac070c80fd4b149b33e56aaaf9235af9e87b0501d91"
		hash = "9efb5932c0753e45504fc9e8444209b92c2bdf22e63b1c1a44e2d52cb62b4548"
		hash = "d40b16307d6434c3281374c0e1bbc0f6db388883e7f6266c3c81de0694266882"
		logic_hash = "0c20163871bf424c0b594c4b75d35e782df03761552f792474761c603ddb8478"
		score = 75
		quality = 85
		tags = "FILE"

	strings:
		$s1 = ".StartInfo.FileName = 'cmd.exe';" ascii
		$s2 = "<xsl:template match=\"\"/root\"\">" ascii fullword
		$s3 = "<?xml version=\"\"1.0\"\"?><root>test</root>\";" ascii fullword

	condition:
		uint16( 0 ) == 0x253c and filesize < 6KB and all of them
}

Strings (3 patterns)

IdentifierTypeValueModifiers
$s1text".StartInfo.FileName = 'cmd.exe';"ascii
$s2text"<xsl:template match=\"\"/root\"\">"ascii fullword
$s3text"<?xml version=\"\"1.0\"\"?><root>test</root>\";"ascii fullword

Condition

uint16( 0 ) == 0x253c and filesize < 6KB and all of them

In plain words (Heuristic)

  • The file must be smaller than 6KB (a cheap guard that skips large files).
  • All patterns in the rule must match.

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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).

  • 10b6e82125a2ddf3cc31a238e0d0c71a64f902e0d77171766713affede03174d
  • 170bee832df176aac0a3c6c7d5aa3fee413b4572030a24c994a97e70f6648ffc
  • 31c4d1fc81c052e269866deff324dffb215e7d481a47a2b6357a572a3e685d90
  • 41b5c26ac194439612b68e9ec6a638eceaf00842c347ffa551eb009ef6c015a3
  • 4b645bc773acde2b3cc204e77ac27c3f6991046c3b75f42d12bc90ec29cff9e3
  • 602bb701b78895d4de32f5e78f3c511e5298ba244b29641b11a7c1c483789859
  • 7ac47a17c511e25c06a53a1c7a5fbbf05f41f047a4a40b71afa81ce7b59f4b03
  • 9a5097d0e8dc29a2814adac070c80fd4b149b33e56aaaf9235af9e87b0501d91
  • 9efb5932c0753e45504fc9e8444209b92c2bdf22e63b1c1a44e2d52cb62b4548
  • d40b16307d6434c3281374c0e1bbc0f6db388883e7f6266c3c81de0694266882

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: 52884135-6b86-5e3e-a866-36a812d5a9af

Tags:FILE

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