XOR_4byte_Key

YARA detection rule by Florian Roth · GPL-2.0

Detects an executable encrypted with a 4 byte XOR (also used for Derusbi Trojan)

rule XOR_4byte_Key
{

    meta:
        description = "Detects an executable encrypted with a 4 byte XOR (also used for Derusbi Trojan)"
        author = "Florian Roth"
        reference = "http://blog.airbuscybersecurity.com/post/2015/11/Newcomers-in-the-Derusbi-family"
        date = "2015-12-15"
        score = 60

   strings:
      
      $s1 = { 85 C9 74 0A 31 06 01 1E 83 C6 04 49 EB F2 }
      

   condition:
      uint16(0) == 0x5a4d and filesize < 900KB and all of them
}

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

c34461a1-831b-4f63-8310-7133cd07d75a

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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

[[ reason ]]

What does this mean?

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.

[[ reason ]]

What do these messages mean?

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

[[ currentRule.title ]]

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