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SIGNATURE_BASE_APT_PY_Esxi_Backdoor_Dec22

Detects Python backdoor found on ESXi servers

APT / threat actorSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Florian Roth
Date
2022-12-14
Modified
2023-12-05
Score / Quality
85 / 85

What this rule detects

Detects Python backdoor found on ESXi servers

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

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
apt-py-esxi-backdoor-dec22.yarDetection Rule License 1.1
rule SIGNATURE_BASE_APT_PY_Esxi_Backdoor_Dec22 : FILE
{
	meta:
		description = "Detects Python backdoor found on ESXi servers"
		author = "Florian Roth"
		id = "f0a3b9b9-0031-5d9f-97f8-70f83863ee63"
		date = "2022-12-14"
		modified = "2023-12-05"
		reference = "https://blogs.juniper.net/en-us/threat-research/a-custom-python-backdoor-for-vmware-esxi-servers"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/mal_ransom_esxi_attacks_feb23.yar#L58-L71"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "86b628f007720aa706c30d91e845d867ed481d1e99bcc9315c84a4e0b7b1b2a6"
		score = 85
		quality = 85
		tags = "FILE"

	strings:
		$x1 = "cmd = str(base64.b64decode(encoded_cmd), " ascii
		$x2 = "sh -i 2>&1 | nc %s %s > /tmp/" ascii

	condition:
		filesize < 10KB and 1 of them or all of them
}

Strings (2 patterns)

IdentifierTypeValueModifiers
$x1text"cmd = str(base64.b64decode(encoded_cmd), "ascii
$x2text"sh -i 2>&1 | nc %s %s > /tmp/"ascii

Condition

filesize < 10KB and 1 of them or all of them

In plain words (Heuristic)

  • The file must be smaller than 10KB (a cheap guard that skips large files).
  • All patterns in the rule must match.
  • At least 1 patterns in the rule must match.

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References

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: f0a3b9b9-0031-5d9f-97f8-70f83863ee63

Tags:FILE

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