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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_MAL_Gopuram_Backdoor_Apr23

Detects Gopuram backdoor

APT / threat actorGopuramSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X (with warnings)
Author
X__Junior (Nextron Systems)
Date
2023-02-24
Modified
2023-12-05
Score / Quality
80 / 85

What this rule detects

Detects Gopuram backdoor

Associated malware family: Gopuram.

Targets: Windows PE.

It defines 4 patterns (1 text, 3 hex, 0 regex). YARA modules used: pe.

YARA-X says: warning[non_bool_expr]: non-boolean expression used as boolean

Summary generated from the rule's metadata and condition.

Rule source

Download .yar

Includes the imports needed to compile it on its own.

apt-mal-gopuram-backdoor-apr23.yarDetection Rule License 1.1
import "pe"

rule SIGNATURE_BASE_APT_MAL_Gopuram_Backdoor_Apr23 : FILE
{
	meta:
		description = "Detects Gopuram backdoor"
		author = "X__Junior (Nextron Systems)"
		id = "3ae5ddcb-5601-5dca-85dd-0a4772577fae"
		date = "2023-02-24"
		modified = "2023-12-05"
		reference = "https://securelist.com/gopuram-backdoor-deployed-through-3cx-supply-chain-attack/109344/"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_mal_gopuram_apr23.yar#L20-L41"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "beb775af5196f30e0ee021790a4978ca7a7ac2a7cf970a5a620ffeb89cc60b2c"
		hash = "97b95b4a5461f950e712b82783930cb2a152ec0288c00a977983ca7788342df7"
		logic_hash = "aa3dd1f35d27d23eb775410cceae81d5b767dc0f1636aac67f2d2e988a3ed995"
		score = 80
		quality = 85
		tags = "FILE"

	strings:
		$x1 = "%s\\config\\TxR\\%s.TxR.0.regtrans-m" ascii
		$xop = { D1 E8 33 C3 D1 EB A8 01 74 ?? 81 F3 25 A3 87 DE D1 E8 33 C3 D1 EB A8 01 74 ?? 81 F3 25 A3 87 DE D1 E8 33 C3 D1 EB A8 01 74 ?? 81 F3 25 A3 87 DE D1 E8 33 C3 D1 EB A8 01 74 ?? 81 F3 25 A3 87 DE }
		$opa1 = { 48 89 44 24 ?? 45 33 C9 45 33 C0 33 D2 89 5C 24 ?? 48 89 74 24 ?? 48 89 5C 24 ?? 89 7C 24 ?? FF 15 ?? ?? ?? ?? 85 C0 74 ?? 48 8B 4C 24 ?? 4C 8D 4C 24 ?? 44 8D 43 }
		$opa2 = { 48 89 B4 24 ?? ?? ?? ?? 44 8D 43 ?? 33 D2 48 89 BC 24 ?? ?? ?? ?? 4C 89 B4 24 ?? ?? ?? ?? E8 ?? ?? ?? ?? 48 8B 4C 24 ?? E8 ?? ?? ?? ?? 48 8B 4C 24 ?? 45 33 C0 33 D2 8B F8 E8 ?? ?? ?? ?? 8D 4F ?? E8 ?? ?? ?? ?? 4C 8B 4C 24 ?? 44 8D 43 ?? 48 8B C8 8B D7 48 8B F0 44 8B F7 E8 ?? ?? ?? ?? 48 8B 4C 24 ?? E8  }

	condition:
		( uint16( 0 ) == 0x5A4D and filesize < 2MB and pe.characteristics & pe.DLL and 1 of ( $x* ) ) or all of ( $opa* )
}

Strings (4 patterns)

IdentifierTypeValueModifiers
$x1text"%s\\config\\TxR\\%s.TxR.0.regtrans-m"ascii
$xophex{ D1 E8 33 C3 D1 EB A8 01 74 ?? 81 F3 25 A3 87 DE D1 E8 33 C3 D1 EB A8 01 74 ?? 81 F3 25 A3 87 DE D1 E8 33 C3 D1 EB A8 01 74 ?? 81 F3 25 A3 87 DE D1 E8 33 C3 D1 …
$opa1hex{ 48 89 44 24 ?? 45 33 C9 45 33 C0 33 D2 89 5C 24 ?? 48 89 74 24 ?? 48 89 5C 24 ?? 89 7C 24 ?? FF 15 ?? ?? ?? ?? 85 C0 74 ?? 48 8B 4C 24 ?? 4C 8D 4C 24 ?? 44 8D …
$opa2hex{ 48 89 B4 24 ?? ?? ?? ?? 44 8D 43 ?? 33 D2 48 89 BC 24 ?? ?? ?? ?? 4C 89 B4 24 ?? ?? ?? ?? E8 ?? ?? ?? ?? 48 8B 4C 24 ?? E8 ?? ?? ?? ?? 48 8B 4C 24 ?? 45 33 C0 …

Condition

( uint16( 0 ) == 0x5A4D and filesize < 2MB and pe.characteristics & pe.DLL and 1 of ( $x* ) ) or all of ( $opa* )

In plain words (Heuristic)

  • The file must start with “MZ” — a Windows executable (PE).
  • The file must be smaller than 2MB (a cheap guard that skips large files).
  • All patterns in ( $opa* ) must match.
  • At least 1 patterns in ( $x* ) must match.
  • Uses the pe module.
  • Requires a DLL.

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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).

  • beb775af5196f30e0ee021790a4978ca7a7ac2a7cf970a5a620ffeb89cc60b2c
  • 97b95b4a5461f950e712b82783930cb2a152ec0288c00a977983ca7788342df7

Licence & attribution

Author: X__Junior (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: 3ae5ddcb-5601-5dca-85dd-0a4772577fae

Tags:FILE

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