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SEKOIA_Apt_Aptc60_Downloader_Strings

Detects a simple downloader abusing wlrmdr.exe and used by APT-C-60

APT / threat actorSEKOIA.IO CommunityDetection Rule License 1.1Compiles with YARA-X
Author
Sekoia.io
Date
2024-09-05
Modified
2024-12-19
Score / Quality
75 / 80

What this rule detects

Detects a simple downloader abusing wlrmdr.exe and used by APT-C-60

Targets: Windows PE.

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

Summary generated from the rule's metadata and condition.

Rule source

apt-aptc60-downloader-strings.yarDetection Rule License 1.1
rule SEKOIA_Apt_Aptc60_Downloader_Strings : FILE
{
	meta:
		description = "Detects a simple downloader abusing wlrmdr.exe and used by APT-C-60"
		author = "Sekoia.io"
		id = "02fd6d5b-7211-46cc-bcff-ab5d78e459c0"
		date = "2024-09-05"
		modified = "2024-12-19"
		reference = "https://github.com/SEKOIA-IO/Community"
		source_url = "https://github.com/SEKOIA-IO/Community/blob/a438a5901a211c2abdf75da9c93921ef187473d1/yara_rules/apt_aptc60_downloader_strings.yar#L1-L20"
		license_url = "https://github.com/SEKOIA-IO/Community/blob/a438a5901a211c2abdf75da9c93921ef187473d1/LICENSE.md"
		hash = "b14ef85a60ac71c669cc960bdf580144"
		logic_hash = "f05480834e6d91a852a190a2ecec05aaea1affa8a605a56c80962a9fbfc8f0c0"
		score = 75
		quality = 80
		tags = "FILE"
		version = "1.0"
		classification = "TLP:CLEAR"

	strings:
		$ = "mydllmain" fullword
		$ = "-s 3600 -f 0 -t _ -m _ -a 11 -u" wide
		$ = "WlrMakeService" wide
		$ = "Trigger1" wide

	condition:
		uint16be( 0 ) == 0x4d5a and all of them and filesize < 500KB
}

Strings (4 patterns)

IdentifierTypeValueModifiers
$text"mydllmain"fullword
$text"-s 3600 -f 0 -t _ -m _ -a 11 -u"wide
$text"WlrMakeService"wide
$text"Trigger1"wide

Condition

uint16be( 0 ) == 0x4d5a and all of them and filesize < 500KB

In plain words (Heuristic)

  • The file must start with “MZ” — a Windows executable (PE).
  • 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

Sample hashes

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

  • b14ef85a60ac71c669cc960bdf580144

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: 02fd6d5b-7211-46cc-bcff-ab5d78e459c0

Metadata

version1.0
classificationTLP:CLEAR

Tags:FILE