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YARA · elceef yara-rulz

ELCEEF_BAT_Obfuscated_Setenv

Detects batch script with obfuscated SET command located directly after @echo off

Suspicious / huntingelceef yara-rulzMIT LicenseCompiles with YARA-X
Author
marcin@ulikowski.pl
Date
2023-05-01
Modified
2023-05-05
Score / Quality
75 / 75

What this rule detects

Detects batch script with obfuscated SET command located directly after @echo off

It defines 2 patterns (0 text, 2 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
bat-obfuscated-setenv.yarMIT License
rule ELCEEF_BAT_Obfuscated_Setenv
{
	meta:
		description = "Detects batch script with obfuscated SET command located directly after @echo off"
		author = "marcin@ulikowski.pl"
		id = "999d192e-a792-5953-b9e2-de4b298444d3"
		date = "2023-05-01"
		modified = "2023-05-05"
		reference = "https://twitter.com/wdormann/status/1651631372438585344"
		source_url = "https://github.com/elceef/yara-rulz/blob/5683b294a12cf0c875b624933586029ae43a852f/rules/Suspicious_BAT.yara#L1-L20"
		license_url = "https://github.com/elceef/yara-rulz/blob/5683b294a12cf0c875b624933586029ae43a852f/LICENSE"
		hash = "a0f43c5748ada07a12af81dda2460045030f936a8d5081f3a403f85c2a9668f8"
		hash = "1a0ca873412474a6437d33e48071aa0169f8317b5c996e1b10a41791707b2cf5"
		hash = "83e47d4f3dd43ed01dc573f0b83e9e71f0ec75b6ea5712f640585d01d8aedf3c"
		hash = "cf351a2b1f0a157a92be2e01e460140e2c1d0ee1685474144f2203a97d2de489"
		logic_hash = "da3a2245207d79cb720079cc2bc88d5f9db22fc16601d21e7c8dcea381ed11e9"
		score = 75
		quality = 75
		tags = ""

	strings:
		$s1 = { 40 65 63 68 6f 20 6f 66 66 0d 0a ( 73 65 25 | 73 25 | 25 ) [2-26] 3a 7e [0-6] 3? 25 ( 25 | 20 | 65 25 | 74 20 | 65 74 20 ) }
		$s2 = { 40 65 63 68 6f 20 6f 66 66 0d 0a 73 65 74 20 22 [4] 3d 73 65 74 20 22 0d 0a 25 }

	condition:
		$s1 in ( 0 .. 4 ) or $s2 in ( 0 .. 4 )
}

Strings (2 patterns)

IdentifierTypeValueModifiers
$s1hex{ 40 65 63 68 6f 20 6f 66 66 0d 0a ( 73 65 25 | 73 25 | 25 ) [2-26] 3a 7e [0-6] 3? 25 ( 25 | 20 | 65 25 | 74 20 | 65 74 20 ) }
$s2hex{ 40 65 63 68 6f 20 6f 66 66 0d 0a 73 65 74 20 22 [4] 3d 73 65 74 20 22 0d 0a 25 }

Condition

$s1 in ( 0 .. 4 ) or $s2 in ( 0 .. 4 )

In plain words (Heuristic)

  • Pattern $s1 must be found within the range 0 .. 4.
  • Pattern $s2 must be found within the range 0 .. 4.

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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).

  • a0f43c5748ada07a12af81dda2460045030f936a8d5081f3a403f85c2a9668f8
  • 1a0ca873412474a6437d33e48071aa0169f8317b5c996e1b10a41791707b2cf5
  • 83e47d4f3dd43ed01dc573f0b83e9e71f0ec75b6ea5712f640585d01d8aedf3c
  • cf351a2b1f0a157a92be2e01e460140e2c1d0ee1685474144f2203a97d2de489

Licence & attribution

Author: marcin@ulikowski.pl

Source repository: elceef yara-rulz @ 5683b294a1

Licence: MIT License (repository licence)

Copyright notice: Copyright (c) 2022 Marcin Ulikowski

Original rule

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

Rule id: 999d192e-a792-5953-b9e2-de4b298444d3

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