Suspicious_PYC_Base85

YARA detection rule by Luke Acha (@luke92881)

Detects suspicious Python bytecode containing marshal/zlib/base64 artifacts and a characteristic encoded data marker

rule Suspicious_PYC_Base85
{
    meta:
        description = "Detects suspicious Python bytecode containing marshal/zlib/base64 artifacts and a characteristic encoded data marker"
        author = "Luke Acha (@luke92881)"
        date = "2026-06-16"
        version = "1.0"
        reference = "Custom detection based on PureRAT Python bytecode samples"
        tlp = "CLEAR"

    strings:
                $b85_marker = { 63 24 7C 63 7? 2A 52 75 30 55 }

                $libs = { 6D 61 72 73 68 61 6C DA 04 7A 6C 69 62 DA 06 62 61 73 65 36 34 }

condition:
    filesize < 5MB and
    $b85_marker in (0..256) and
    $libs  in (0..256)
}

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

894f3f87-b9dc-4bdd-ba52-be048ad7e5ce

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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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