Skip to content
yararules.org
Menu

YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_HKTL_Proxy_Tool_Jun23_1

Detects agent used as proxy tool in UNC4841 intrusions - possibly Alchemist C2 framework implant

APT / threat actorSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Florian Roth
Date
2023-06-16
Modified
2023-12-05
Score / Quality
75 / 85

What this rule detects

Detects agent used as proxy tool in UNC4841 intrusions - possibly Alchemist C2 framework implant

Targets: Windows PE, Linux ELF.

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
apt-hktl-proxy-tool-jun23-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_APT_HKTL_Proxy_Tool_Jun23_1 : FILE
{
	meta:
		description = "Detects agent used as proxy tool in UNC4841 intrusions - possibly Alchemist C2 framework implant"
		author = "Florian Roth"
		id = "0e406737-3083-53c2-a6d2-14c07794125a"
		date = "2023-06-16"
		modified = "2023-12-05"
		reference = "https://www.mandiant.com/resources/blog/barracuda-esg-exploited-globally"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_barracuda_esg_unc4841_jun23.yar#L76-L101"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "ca72fa64ed0a9c22d341a557c6e7c1b6a7264b0c4de0b6f717dd44bddf550bca"
		hash = "57e4b180fd559f15b59c43fb3335bd59435d4d76c4676e51a06c6b257ce67fb2"
		logic_hash = "7e2152e1aa74e1842519e2eecd2acd3ef8eb8d517f3c0ef9f05c983616f223c3"
		score = 75
		quality = 85
		tags = "FILE"

	strings:
		$a2 = "/src/runtime/panic.go"
		$s1 = "main.handleClientRequest" ascii fullword
		$s2 = "main.sockIP.toAddr" ascii fullword

	condition:
		( uint16( 0 ) == 0x5a4d or uint32be( 0 ) == 0x7f454c46 or uint16( 0 ) == 0xfeca or uint16( 0 ) == 0xfacf or uint32( 0 ) == 0xbebafeca or uint32( 0 ) == 0xbebafeca ) and filesize < 10MB and all of them
}

Strings (3 patterns)

IdentifierTypeValueModifiers
$a2text"/src/runtime/panic.go"
$s1text"main.handleClientRequest"ascii fullword
$s2text"main.sockIP.toAddr"ascii fullword

Condition

( uint16( 0 ) == 0x5a4d or uint32be( 0 ) == 0x7f454c46 or uint16( 0 ) == 0xfeca or uint16( 0 ) == 0xfacf or uint32( 0 ) == 0xbebafeca or uint32( 0 ) == 0xbebafeca ) and filesize < 10MB and all of them

In plain words (Heuristic)

  • The file must start with “MZ” — a Windows executable (PE).
  • The file must start with the ELF header — a Linux/Unix executable.
  • The file must be smaller than 10MB (a cheap guard that skips large files).
  • All patterns in the rule must match.

Test this rule in your browser

Drop a file to scan it with this rule using YARA-X compiled to WebAssembly. Nothing is uploaded.

Drop a file here or click to chooseScanned locally with YARA-X. Files up to 200 MB.

Open in editor

References

Sample hashes

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

  • ca72fa64ed0a9c22d341a557c6e7c1b6a7264b0c4de0b6f717dd44bddf550bca
  • 57e4b180fd559f15b59c43fb3335bd59435d4d76c4676e51a06c6b257ce67fb2

Licence & attribution

Author: Florian Roth

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: 0e406737-3083-53c2-a6d2-14c07794125a

Tags:FILE

Related rules