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SEKOIA_Rootkit_Win_Purplefox_Svchost_Txt

Detects Purple Fox payloads used during end-2021 and 2022 campaigns based on characteristics shared by TrendMicro details.

MalwarePurplefoxSEKOIA.IO CommunityDetection Rule License 1.1Compiles with YARA-X
Author
Sekoia.io
Date
2022-03-28
Modified
2024-12-19
Score / Quality
75 / 80

What this rule detects

Detects Purple Fox payloads used during end-2021 and 2022 campaigns based on characteristics shared by TrendMicro details.

Associated malware family: Purplefox.

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

Summary generated from the rule's metadata and condition.

Rule source

rootkit-win-purplefox-svchost-txt.yarDetection Rule License 1.1
rule SEKOIA_Rootkit_Win_Purplefox_Svchost_Txt : FILE
{
	meta:
		description = "Detects Purple Fox payloads used during end-2021 and 2022 campaigns based on characteristics shared by TrendMicro details."
		author = "Sekoia.io"
		id = "e992d574-6a44-4bea-97e2-6d5579ce8d02"
		date = "2022-03-28"
		modified = "2024-12-19"
		reference = "https://www.trendmicro.com/en_us/research/22/c/purple-fox-uses-new-arrival-vector-and-improves-malware-arsenal.html"
		source_url = "https://github.com/SEKOIA-IO/Community/blob/a438a5901a211c2abdf75da9c93921ef187473d1/yara_rules/rootkit_win_purplefox_svchost_txt.yar#L1-L22"
		license_url = "https://github.com/SEKOIA-IO/Community/blob/a438a5901a211c2abdf75da9c93921ef187473d1/LICENSE.md"
		logic_hash = "a1de949cb2e898ed031f5c796f7152af12dfae5431dfaf269f25ebe72f0ae004"
		score = 75
		quality = 80
		tags = "FILE"
		version = "1.0"
		classification = "TLP:CLEAR"

	strings:
		$str0 = "C:\\ProgramData\\dll.dll,luohua" wide
		$str1 = "C:\\ProgramData\\7z.exe" wide
		$str2 = "F:\\hidden-master\\x64\\Debug\\QAssist.pdb" ascii
		$str3 = "F:\\Root\\sources\\MedaiUpdateV8\\Release\\MedaiUpdateV8.pdb" ascii
		$str4 = "cmd.exe /c RunDll32.exe InetCpl.cpl,ClearMyTracksByProcess 255" ascii
		$str5 = "del /s /f %appdata%\\Mozilla\\Firefox\\Profiles\\*.db" ascii

	condition:
		4 of ( $str* ) and filesize > 7000KB and filesize < 9500KB
}

Strings (6 patterns)

IdentifierTypeValueModifiers
$str0text"C:\\ProgramData\\dll.dll,luohua"wide
$str1text"C:\\ProgramData\\7z.exe"wide
$str2text"F:\\hidden-master\\x64\\Debug\\QAssist.pdb"ascii
$str3text"F:\\Root\\sources\\MedaiUpdateV8\\Release\\MedaiUpdateV8.pdb"ascii
$str4text"cmd.exe /c RunDll32.exe InetCpl.cpl,ClearMyTracksByProcess 255"ascii
$str5text"del /s /f %appdata%\\Mozilla\\Firefox\\Profiles\\*.db"ascii

Condition

4 of ( $str* ) and filesize > 7000KB and filesize < 9500KB

In plain words (Heuristic)

  • The file must be smaller than 9500KB (a cheap guard that skips large files).
  • The file must be larger than 7000KB.
  • At least 4 patterns in ( $str* ) must match.

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References

Licence & attribution

Author: Sekoia.io

Source repository: SEKOIA.IO Community @ a438a5901a

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: e992d574-6a44-4bea-97e2-6d5579ce8d02

Metadata

version1.0
classificationTLP:CLEAR

Tags:FILE

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