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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_WEBSHELL_Proxyshell_Exploitation_Nov21_1

Detects webshells dropped by DropHell malware

WebshellSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Florian Roth (Nextron Systems)
Date
2021-11-01
Modified
2025-11-03
Score / Quality
85 / 85

What this rule detects

Detects webshells dropped by DropHell malware

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
webshell-proxyshell-exploitation-nov21-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_WEBSHELL_Proxyshell_Exploitation_Nov21_1
{
	meta:
		description = "Detects webshells dropped by DropHell malware"
		author = "Florian Roth (Nextron Systems)"
		id = "300eaadf-db0c-5591-84fc-abdf7cdd90c1"
		date = "2021-11-01"
		modified = "2025-11-03"
		reference = "https://www.deepinstinct.com/blog/do-not-exchange-it-has-a-shell-inside"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/expl_proxyshell.yar#L257-L271"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "d9812d3f53c346c4e318609e0c7de66811b27ffa7528a6ddeb6ac8436da59ef5"
		score = 85
		quality = 85
		tags = ""

	strings:
		$s01 = ".LoadXml(System.Text.Encoding.UTF8.GetString(System.Convert.FromBase64String(Request[" ascii wide
		$s02 = "new System.IO.MemoryStream()" ascii wide
		$s03 = "Transform(" ascii wide

	condition:
		all of ( $s* )
}

Strings (3 patterns)

IdentifierTypeValueModifiers
$s01text".LoadXml(System.Text.Encoding.UTF8.GetString(System.Convert.FromBase64String(Request["ascii wide
$s02text"new System.IO.MemoryStream()"ascii wide
$s03text"Transform("ascii wide

Condition

all of ( $s* )

In plain words (Heuristic)

  • All patterns in ( $s* ) 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: 300eaadf-db0c-5591-84fc-abdf7cdd90c1

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