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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_SUSP_Base64_Encoded_Exploit_Indicators_Dec21

Detects base64 encoded strings found in payloads of exploits against log4j CVE-2021-44228

Suspicious / huntingSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Florian Roth (Nextron Systems)
Date
2021-12-10
Modified
2021-12-13
Score / Quality
70 / 85

What this rule detects

Detects base64 encoded strings found in payloads of exploits against log4j CVE-2021-44228

It defines 7 patterns (7 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
susp-base64-encoded-exploit-indicators-dec21.yarDetection Rule License 1.1
rule SIGNATURE_BASE_SUSP_Base64_Encoded_Exploit_Indicators_Dec21 : CVE_2021_44228
{
	meta:
		description = "Detects base64 encoded strings found in payloads of exploits against log4j CVE-2021-44228"
		author = "Florian Roth (Nextron Systems)"
		id = "09abc4f0-ace7-5f53-b1d3-5f5c6bf3bdba"
		date = "2021-12-10"
		modified = "2021-12-13"
		reference = "https://twitter.com/Reelix/status/1469327487243071493"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/expl_log4j_cve_2021_44228.yar#L142-L165"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "703a83916c7279bcdc3cd61602472c2a3815140235be169f5b2063a547438c61"
		score = 70
		quality = 85
		tags = "CVE-2021-44228"

	strings:
		$sa1 = "Y3VybCAtcy"
		$sa2 = "N1cmwgLXMg"
		$sa3 = "jdXJsIC1zI"
		$sb1 = "fHdnZXQgLXEgLU8tI"
		$sb2 = "x3Z2V0IC1xIC1PLS"
		$sb3 = "8d2dldCAtcSAtTy0g"
		$fp1 = "<html"

	condition:
		1 of ( $sa* ) and 1 of ( $sb* ) and not 1 of ( $fp* )
}

Strings (7 patterns)

IdentifierTypeValueModifiers
$sa1text"Y3VybCAtcy"
$sa2text"N1cmwgLXMg"
$sa3text"jdXJsIC1zI"
$sb1text"fHdnZXQgLXEgLU8tI"
$sb2text"x3Z2V0IC1xIC1PLS"
$sb3text"8d2dldCAtcSAtTy0g"
$fp1text"<html"

Condition

1 of ( $sa* ) and 1 of ( $sb* ) and not 1 of ( $fp* )

In plain words (Heuristic)

  • At least 1 patterns in ( $sa* ) must match.
  • At least 1 patterns in ( $sb* ) must match.
  • At least 1 patterns in ( $fp* ) must match.

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References

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: 09abc4f0-ace7-5f53-b1d3-5f5c6bf3bdba

Tags:CVE_2021_44228

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