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May 11

Detecting Mimikatz Use

Benjamin Delpy published some YARA rules in detecting Mimikatz use in your environment.
More information on Mimikatz capability is in the Unofficial Mimikatz Guide & Command Reference” on this site.

YARA is described as:

YARA is a tool aimed at (but not limited to) helping malware researchers to identify and classify malware samples. With YARA you can create descriptions of malware families (or whatever you want to describe) based on textual or binary patterns. Each description, a.k.a rule, consists of a set of strings and a boolean expression which determine its logic.

YARA is multi-platform, running on Windows, Linux and Mac OS X, and can be used through its command-line interface or from your own Python scripts with the yara-python extension.

Based on the published data, this data enables detection of the Mimikatz exe, dll, and artifacts such as kirbi ticket files, as well as WCE.
Here’s the data:

/*    Benjamin DELPY `gentilkiwi`
http://blog.gentilkiwi.com
benjamin@gentilkiwi.com
Licence : http://creativecommons.org/licenses/by/3.0/fr/
*/
rule mimikatz
{
meta:
description        = “mimikatz”
author            = “Benjamin DELPY (gentilkiwi)”
tool_author        = “Benjamin DELPY (gentilkiwi)”
strings:
$exe_x86_1        = { 89 71 04 89 [0-3] 30 8d 04 bd }
$exe_x86_2        = { 89 79 04 89 [0-3] 38 8d 04 b5 }

$exe_x64_1        = { 4c 03 d8 49 [0-3] 8b 03 48 89 }
$exe_x64_2        = { 4c 8b df 49 [0-3] c1 e3 04 48 [0-3] 8b cb 4c 03 [0-3] d8 }

$dll_1            = {    c7 0? 00 00 01 00 [4-14] c7 0? 01 00 00 00 }
$dll_2            = { c7 0? 10 02 00 00 ?? 89 4? }

$sys_x86        = { a0 00 00 00 24 02 00 00 40 00 00 00 [0-4] b8 00 00 00 6c 02 00 00 40 00 00 00 }
$sys_x64        = { 88 01 00 00 3c 04 00 00 40 00 00 00 [0-4] e8 02 00 00 f8 02 00 00 40 00 00 00 }
condition:
(all of ($exe_x86_*)) or (all of ($exe_x64_*)) or (all of ($dll_*)) or (any of ($sys_*))
}

rule mimikatz_lsass_mdmp
{
meta:
description        = “LSASS minidump file for mimikatz”
author            = “Benjamin DELPY (gentilkiwi)”
strings:
$lsass            = “System32\\lsass.exe”    wide nocase
condition:
(uint32(0) == 0x504d444d) and $lsass
}

rule mimikatz_kirbi_ticket
{
meta:
description        = “KiRBi ticket for mimikatz”
author            = “Benjamin DELPY (gentilkiwi)”
strings:
$asn1            = { 76 82 ?? ?? 30 82 ?? ?? a0 03 02 01 05 a1 03 02 01 16 }
condition:
$asn1 at 0
}

rule wce
{
meta:
description        = “wce”
author            = “Benjamin DELPY (gentilkiwi)”
tool_author        = “Hernan Ochoa (hernano)”
strings:
$hex_legacy        = { 8b ff 55 8b ec 6a 00 ff 75 0c ff 75 08 e8 [0-3] 5d c2 08 00 }
$hex_x86        = { 8d 45 f0 50 8d 45 f8 50 8d 45 e8 50 6a 00 8d 45 fc 50 [0-8] 50 72 69 6d 61 72 79 00 }
$hex_x64        = { ff f3 48 83 ec 30 48 8b d9 48 8d 15 [0-16] 50 72 69 6d 61 72 79 00 }
condition:
any of them
}



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