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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_SUSP_OBFUSC_Indiators_XML_Officedoc_Sep21_2

Detects suspicious encodings in fields used in reference files found in weaponized MS Office documents

Suspicious / huntingSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Florian Roth (Nextron Systems)
Date
2021-09-18
Modified
2023-12-05
Score / Quality
65 / 85

What this rule detects

Detects suspicious encodings in fields used in reference files found in weaponized MS Office documents

It defines 4 patterns (4 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
susp-obfusc-indiators-xml-officedoc-sep21-2.yarDetection Rule License 1.1
rule SIGNATURE_BASE_SUSP_OBFUSC_Indiators_XML_Officedoc_Sep21_2 : WINDOWS CVE FILE
{
	meta:
		description = "Detects suspicious encodings in fields used in reference files found in weaponized MS Office documents"
		author = "Florian Roth (Nextron Systems)"
		id = "c3c5ec4f-5d2a-523c-bd4b-b75c04bac87d"
		date = "2021-09-18"
		modified = "2023-12-05"
		reference = "https://twitter.com/sudosev/status/1439205606129377282"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/expl_cve_2021_40444.yar#L83-L98"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "82c70e0f0b72a57302e5853cc53ae18dbb0bc8dabdfd27b473a7664b2fc5e874"
		score = 65
		quality = 85
		tags = "WINDOWS, CVE, FILE"

	strings:
		$h1 = "<?xml " ascii wide
		$a1 = "Target" ascii wide
		$a2 = "TargetMode" ascii wide
		$xml_e = "&#x0000" ascii wide

	condition:
		filesize < 500KB and all of them
}

Strings (4 patterns)

IdentifierTypeValueModifiers
$h1text"<?xml "ascii wide
$a1text"Target"ascii wide
$a2text"TargetMode"ascii wide
$xml_etext"&#x0000"ascii wide

Condition

filesize < 500KB and all of them

In plain words (Heuristic)

  • The file must be smaller than 500KB (a cheap guard that skips large files).
  • All patterns in the rule 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: c3c5ec4f-5d2a-523c-bd4b-b75c04bac87d

Tags:WINDOWSCVEFILE

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