YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_UNC2447_MAL_SOMBRAT_May21_1

Detects SombRAT samples from UNC2447 campaign

APT / threat actorSombratSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X

Author: Florian Roth (Nextron Systems)
Date: 2021-05-01
Modified: 2023-01-07
Score / Quality: 75 / 85

What this rule detects

Detects SombRAT samples from UNC2447 campaign

Associated malware family: Sombrat.

Targets: Windows PE.

It defines 9 patterns (5 text, 4 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar

apt-unc2447-mal-sombrat-may21-1.yarDetection Rule License 1.1

rule SIGNATURE_BASE_APT_UNC2447_MAL_SOMBRAT_May21_1 : FILE
{
	meta:
		description = "Detects SombRAT samples from UNC2447 campaign"
		author = "Florian Roth (Nextron Systems)"
		id = "78b46bed-4fd4-596f-bba7-12243f467af3"
		date = "2021-05-01"
		modified = "2023-01-07"
		reference = "https://www.fireeye.com/blog/threat-research/2021/04/unc2447-sombrat-and-fivehands-ransomware-sophisticated-financial-threat.html"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_unc2447_sombrat.yar#L2-L36"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "61e286c62e556ac79b01c17357176e58efb67d86c5d17407e128094c3151f7f9"
		hash = "99baffcd7a6b939b72c99af7c1e88523a50053ab966a079d9bf268aff884426e"
		logic_hash = "6f2572745cbd68c5f2be5c64b160d2513938daba6da57523012491acc63cfee4"
		score = 75
		quality = 85
		tags = "FILE"

	strings:
		$x1 = "~arungvc" ascii fullword
		$s1 = "plugin64_" ascii
		$s2 = "0xUnknown" ascii fullword
		$s3 = "b%x.%s" ascii fullword
		$s4 = "/news" ascii
		$sc1 = { 00 73 00 65 00 72 00 76 00 69 00 63 00 65 00 73
               00 2E 00 65 00 78 00 65 00 00 00 00 00 00 00 00
               00 49 73 57 6F 77 36 34 50 72 6F 63 65 73 73 00
               00 6B 00 65 00 72 00 6E 00 65 00 6C 00 33 00 32
               00 00 00 00 00 00 00 00 00 47 00 6C 00 6F 00 62
               00 61 00 6C 00 5C 00 25 00 73 }
		$op1 = { 66 90 0f b6 45 80 32 44 0d 81 34 de 88 44 0d 81 48 ff c1 48 83 f9 19 72 e9 }
		$op2 = { 48 8b d0 66 0f 6f 05 ?1 ?? 0? 00 f3 0f 7f 44 24 68 66 89 7c 24 58 41 b8 10 00 00 00 4c 39 40 10 4c 0f 42 40 10 48 83 78 18 08 }
		$op3 = { 49 f7 b0 a0 00 00 00 42 0f b6 04 0a 41 30 44 33 fe 48 83 79 18 10 72 03 48 8b 09 33 d2 b8 05 00 00 00 }

	condition:
		uint16( 0 ) == 0x5a4d and filesize < 3000KB and ( ( 1 of ( $x* ) and 1 of ( $s* ) ) or 3 of them ) or 5 of them
}

Strings (9 patterns)

Identifier	Type	Value	Modifiers
$x1	text	"~arungvc"	ascii fullword
$s1	text	"plugin64_"	ascii
$s2	text	"0xUnknown"	ascii fullword
$s3	text	"b%x.%s"	ascii fullword
$s4	text	"/news"	ascii
$sc1	hex	{ 00 73 00 65 00 72 00 76 00 69 00 63 00 65 00 73 00 2E 00 65 00 78 00 65 00 00 00 00 00 00 00 00 00 49 73 57 6F 77 36 34 50 72 6F …
$op1	hex	{ 66 90 0f b6 45 80 32 44 0d 81 34 de 88 44 0d 81 48 ff c1 48 83 f9 19 72 e9 }
$op2	hex	{ 48 8b d0 66 0f 6f 05 ?1 ?? 0? 00 f3 0f 7f 44 24 68 66 89 7c 24 58 41 b8 10 00 00 00 4c 39 40 10 4c 0f 42 40 10 48 83 78 18 08 }
$op3	hex	{ 49 f7 b0 a0 00 00 00 42 0f b6 04 0a 41 30 44 33 fe 48 83 79 18 10 72 03 48 8b 09 33 d2 b8 05 00 00 00 }

Condition

uint16( 0 ) == 0x5a4d and filesize < 3000KB and ( ( 1 of ( $x* ) and 1 of ( $s* ) ) or 3 of them ) or 5 of them

In plain words (Heuristic)

The file must start with “MZ” — a Windows executable (PE).
The file must be smaller than 3000KB (a cheap guard that skips large files).
At least 1 patterns in ( $x* ) must match.
At least 1 patterns in ( $s* ) must match.
At least 3 patterns in the rule must match.
At least 5 patterns in the rule must match.

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References

https://www.fireeye.com/blog/threat-research/2021/04/unc2447-sombrat-and-fivehands-ransomware-sophisticated-financial-threat.html

Sample hashes

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

61e286c62e556ac79b01c17357176e58efb67d86c5d17407e128094c3151f7f9
99baffcd7a6b939b72c99af7c1e88523a50053ab966a079d9bf268aff884426e

Licence & attribution

Author: Florian Roth (Nextron Systems)

Source repository: Signature Base (Florian Roth / Nextron) @ 94a1c48d7a

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: 78b46bed-4fd4-596f-bba7-12243f467af3

Tags:FILE

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