Skip to content
yararules.org
Menu

YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_WEBSHELL_ASPX_Proxyshell_Exploitation_Aug21_1

Detects unknown malicious loaders noticed in August 2021

WebshellSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Florian Roth (Nextron Systems)
Date
2021-08-25
Modified
2025-11-03
Score / Quality
90 / 85

What this rule detects

Detects unknown malicious loaders noticed in August 2021

It defines 1 patterns (1 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
webshell-aspx-proxyshell-exploitation-aug21-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_WEBSHELL_ASPX_Proxyshell_Exploitation_Aug21_1 : FILE
{
	meta:
		description = "Detects unknown malicious loaders noticed in August 2021"
		author = "Florian Roth (Nextron Systems)"
		id = "1fa563fc-c91c-5f4e-98f1-b895e1acb4f4"
		date = "2021-08-25"
		modified = "2025-11-03"
		reference = "https://twitter.com/VirITeXplorer/status/1430206853733097473"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/expl_proxyshell.yar#L107-L119"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "8a2417bb85c7f91d98143d2f4c26d30416b3a01ba8abc1445ccfae5609825b4d"
		score = 90
		quality = 85
		tags = "FILE"

	strings:
		$x1 = ");eval/*asf" ascii

	condition:
		filesize < 600KB and 1 of them
}

Strings (1 patterns)

IdentifierTypeValueModifiers
$x1text");eval/*asf"ascii

Condition

filesize < 600KB and 1 of them

In plain words (Heuristic)

  • The file must be smaller than 600KB (a cheap guard that skips large files).
  • At least 1 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.

Open in editor

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: 1fa563fc-c91c-5f4e-98f1-b895e1acb4f4

Tags:FILE

Related rules