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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_WEBSHELL_Cookie_Post_Obfuscation

Detects webshell using cookie POST

WebshellSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Arnim Rupp (https://github.com/ruppde)
Date
2023-01-28
Modified
2023-04-05
Score / Quality
75 / 85

What this rule detects

Detects webshell using cookie POST

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
webshell-cookie-post-obfuscation.yarDetection Rule License 1.1
rule SIGNATURE_BASE_WEBSHELL_Cookie_Post_Obfuscation : FILE
{
	meta:
		description = "Detects webshell using cookie POST"
		author = "Arnim Rupp (https://github.com/ruppde)"
		id = "cc5ded80-5e58-5b25-86d1-1c492042c740"
		date = "2023-01-28"
		modified = "2023-04-05"
		reference = "https://github.com/SigmaHQ/Detection-Rule-License/blob/main/LICENSE.Detection.Rules.md"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/gen_webshells.yar#L6883-L6909"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "d08a00e56feb78b7f6599bad6b9b1d8626ce9a6ea1dfdc038358f4c74e6f65c9"
		hash = "2ce5c4d31682a5a59b665905a6f698c280451117e4aa3aee11523472688edb31"
		hash = "ff732d91a93dfd1612aed24bbb4d13edb0ab224d874f622943aaeeed4356c662"
		hash = "a3b64e9e065602d2863fcab641c75f5d8ec67c8632db0f78ca33ded0f4cea257"
		hash = "d41abce305b0dc9bd3a9feb0b6b35e8e39db9e75efb055d0b1205a9f0c89128e"
		hash = "333560bdc876fb0186fae97a58c27dd68123be875d510f46098fc5a61615f124"
		hash = "2efdb79cdde9396ff3dd567db8876607577718db692adf641f595626ef64d3a4"
		hash = "e1bd3be0cf525a0d61bf8c18e3ffaf3330c1c27c861aede486fd0f1b6930f69a"
		hash = "f8cdedd21b2cc29497896ec5b6e5863cd67cc1a798d929fd32cdbb654a69168a"
		logic_hash = "87229859ca3ee8f8b79360603c421528cda2ecefcc46d4080236d09b2dd510fb"
		score = 75
		quality = 85
		tags = "FILE"
		importance = 70

	strings:
		$s1 = "]($_COOKIE, $_POST) as $"
		$s2 = "function"
		$s3 = "Array"

	condition:
		( uint16( 0 ) == 0x3f3c and filesize < 100KB and ( all of them ) )
}

Strings (3 patterns)

IdentifierTypeValueModifiers
$s1text"]($_COOKIE, $_POST) as $"
$s2text"function"
$s3text"Array"

Condition

( uint16( 0 ) == 0x3f3c and 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.

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References

Sample hashes

Hashes of samples the author lists in the rule's meta (look them up in your threat-intelligence platform).

  • d08a00e56feb78b7f6599bad6b9b1d8626ce9a6ea1dfdc038358f4c74e6f65c9
  • 2ce5c4d31682a5a59b665905a6f698c280451117e4aa3aee11523472688edb31
  • ff732d91a93dfd1612aed24bbb4d13edb0ab224d874f622943aaeeed4356c662
  • a3b64e9e065602d2863fcab641c75f5d8ec67c8632db0f78ca33ded0f4cea257
  • d41abce305b0dc9bd3a9feb0b6b35e8e39db9e75efb055d0b1205a9f0c89128e
  • 333560bdc876fb0186fae97a58c27dd68123be875d510f46098fc5a61615f124
  • 2efdb79cdde9396ff3dd567db8876607577718db692adf641f595626ef64d3a4
  • e1bd3be0cf525a0d61bf8c18e3ffaf3330c1c27c861aede486fd0f1b6930f69a
  • f8cdedd21b2cc29497896ec5b6e5863cd67cc1a798d929fd32cdbb654a69168a

Licence & attribution

Author: Arnim Rupp (https://github.com/ruppde)

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: cc5ded80-5e58-5b25-86d1-1c492042c740

Metadata

importance70

Tags:FILE

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