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DITEKSHEN_MALWARE_Win_Fakecaptcha_Downloader

Detects downloader executables dropped by fake captcha

MalwareFakecaptchaditekSHen detectionBSD 2-Clause LicenseCompiles with YARA-X
Author
ditekshen
Date
2020-11-06
Modified
2024-11-01
Score / Quality
75 / 75

What this rule detects

Detects downloader executables dropped by fake captcha

Associated malware family: Fakecaptcha.

Targets: Windows PE.

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
malware-win-fakecaptcha-downloader.yarBSD 2-Clause License
rule DITEKSHEN_MALWARE_Win_Fakecaptcha_Downloader : FILE
{
	meta:
		description = "Detects downloader executables dropped by fake captcha"
		author = "ditekshen"
		id = "d577e8ef-11df-565c-9925-63b8768a7115"
		date = "2020-11-06"
		modified = "2024-11-01"
		reference = "https://github.com/ditekshen/detection"
		source_url = "https://github.com/ditekshen/detection/blob/e76c93dcdedff04076380ffc60ea54e45b313635/yara/malware.yar#L11793-L11803"
		license_url = "https://github.com/ditekshen/detection/blob/e76c93dcdedff04076380ffc60ea54e45b313635/LICENSE.txt"
		logic_hash = "57c39ce93f74d03767e7fde53281983a8462e4f3705d1bb9084bc169a08a0f83"
		score = 75
		quality = 75
		tags = "FILE"

	strings:
		$s1 = "</script>MZ" ascii
		$s2 = "window.close();" ascii
		$s3 = "eval(" ascii

	condition:
		uint16( 0 ) == 0x5a4d and all of them
}

Strings (3 patterns)

IdentifierTypeValueModifiers
$s1text"</script>MZ"ascii
$s2text"window.close();"ascii
$s3text"eval("ascii

Condition

uint16( 0 ) == 0x5a4d and all of them

In plain words (Heuristic)

  • The file must start with “MZ” — a Windows executable (PE).
  • All patterns in the rule must match.

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References

Licence & attribution

Author: ditekshen

Source repository: ditekSHen detection @ e76c93dcde

Licence: BSD 2-Clause License (repository licence)

Copyright notice: Copyright 2021 by ditekSHen (https://github.com/ditekshen/detection).

Original rule

Mirrored via YARA Forge 20260927, which prefixes rule names with the source and adds normalised meta fields.

Rule id: d577e8ef-11df-565c-9925-63b8768a7115

Tags:FILE

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