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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_WEBSHELL_PAS_Webshell

Detects P.A.S. PHP webshell - Based on DHS/FBI JAR-16-2029 (Grizzly Steppe)

WebshellSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
FR/ANSSI/SDO (modified by Florian Roth)
Date
2021-02-15
Modified
2024-05-25
Score / Quality
70 / 85

What this rule detects

Detects P.A.S. PHP webshell - Based on DHS/FBI JAR-16-2029 (Grizzly Steppe)

It defines 6 patterns (6 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
webshell-pas-webshell.yarDetection Rule License 1.1
rule SIGNATURE_BASE_WEBSHELL_PAS_Webshell : FILE
{
	meta:
		description = "Detects P.A.S. PHP webshell - Based on DHS/FBI JAR-16-2029 (Grizzly  Steppe)"
		author = "FR/ANSSI/SDO (modified by Florian Roth)"
		id = "862aab77-936e-524c-8669-4f48730f4ed5"
		date = "2021-02-15"
		modified = "2024-05-25"
		reference = "https://www.cert.ssi.gouv.fr/uploads/CERTFR-2021-CTI-005.pdf"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_sandworm_centreon.yar#L10-L28"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "977ee0fdf0e92ccea6b71fea7b2c7aed2965c6966d8af86230ccb0f95b286694"
		score = 70
		quality = 85
		tags = "FILE"

	strings:
		$php = "<?php"
		$strreplace = "(str_replace("
		$md5 = ".substr(md5(strrev($"
		$gzinflate = "gzinflate"
		$cookie = "_COOKIE"
		$isset = "isset"

	condition:
		( filesize > 20KB and filesize < 200KB ) and all of them
}

Strings (6 patterns)

IdentifierTypeValueModifiers
$phptext"<?php"
$strreplacetext"(str_replace("
$md5text".substr(md5(strrev($"
$gzinflatetext"gzinflate"
$cookietext"_COOKIE"
$issettext"isset"

Condition

( filesize > 20KB and filesize < 200KB ) and all of them

In plain words (Heuristic)

  • The file must be smaller than 200KB (a cheap guard that skips large files).
  • The file must be larger than 20KB.
  • All patterns in the rule must match.

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References

Licence & attribution

Author: FR/ANSSI/SDO (modified by Florian Roth)

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: 862aab77-936e-524c-8669-4f48730f4ed5

Tags:FILE

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