SUSP_3CX_MSI_Signed_Binary_Mar23_1

YARA detection rule by Florian Roth (Nextron Systems) · NOASSERTION

Detects 3CX MSI installers signed with a known compromised certificate and signed in a time frame in which other known malicious binaries have been signed

rule SUSP_3CX_MSI_Signed_Binary_Mar23_1 {
   meta:
      description = "Detects 3CX MSI installers signed with a known compromised certificate and signed in a time frame in which other known malicious binaries have been signed"
      author = "Florian Roth (Nextron Systems)"
      date = "2023-03-29"
      reference = "https://www.reddit.com/r/crowdstrike/comments/125r3uu/20230329_situational_awareness_crowdstrike/"
      score = 60
      hash1 = "aa124a4b4df12b34e74ee7f6c683b2ebec4ce9a8edcf9be345823b4fdcf5d868"
      hash2 = "59e1edf4d82fae4978e97512b0331b7eb21dd4b838b850ba46794d9c7a2c0983"
      id = "15d6d8ca-6982-5095-9879-ce97269a71c6"
   strings:
      $a1 = { 84 10 0C 00 00 00 00 00 C0 00 00 00 00 00 00 46 } 
      $sc1 = { 1B 66 11 DF 9C 9A 4D 6E CC 8E D5 0C 9B 91 78 73 } 
      $s1 = "3CX Ltd1"
      $s2 = "202303"    condition:
      uint16(0) == 0xcfd0
      and $a1 
      and $sc1 
      and (
         $s1 in (filesize-20000..filesize)
         and $s2 in (filesize-20000..filesize)
      )
}

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

f5766b45-5dda-4a40-a9d5-2f8b7a3ead16

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

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