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WEBSHELL_PHP_OBFUSC_Tiny

YARA detection rule by Arnim Rupp (https://github.com/ruppde) · Detection Rule License 1.1 https://github.com/Neo23x0/signature-base/blob/master/LICENSE

PHP webshell obfuscated

rule WEBSHELL_PHP_OBFUSC_Tiny
{
    meta:
        description = "PHP webshell obfuscated"
        license = "Detection Rule License 1.1 https://github.com/Neo23x0/signature-base/blob/master/LICENSE"
        author = "Arnim Rupp (https://github.com/ruppde)"
        reference = "Internal Research"
        score = 75
        date = "2021/01/12"
        modified = "2024-03-11"
        hash = "b7b7aabd518a2f8578d4b1bc9a3af60d155972f1"
        hash = "694ec6e1c4f34632a9bd7065f73be473"
        hash = "5c871183444dbb5c8766df6b126bd80c624a63a16cc39e20a0f7b002216b2ba5"

        id = "d78e495f-54d2-5f5f-920f-fb6612afbca3"
    strings:
                $obf1 = /\w'\.'\w/ wide ascii
        $obf2 = /\w\"\.\"\w/ wide ascii
        $obf3 = "].$" wide ascii

                                $gfp1  = "eval(\"return [$serialised_parameter"         $gfp2  = "$this->assert(strpos($styles, $"
        $gfp3  = "$module = new $_GET['module']($_GET['scope']);"
        $gfp4  = "$plugin->$_POST['action']($_POST['id']);"
        $gfp5  = "$_POST[partition_by]($_POST["
        $gfp6  = "$object = new $_REQUEST['type']($_REQUEST['id']);"
        $gfp7  = "The above example code can be easily exploited by passing in a string such as"         $gfp8  = "Smarty_Internal_Debug::start_render($_template);"
        $gfp9  = "?p4yl04d=UNION%20SELECT%20'<?%20system($_GET['command']);%20?>',2,3%20INTO%20OUTFILE%20'/var/www/w3bsh3ll.php"
        $gfp10 = "[][}{;|]\\|\\\\[+=]\\|<?=>?"
        $gfp11 = "(eval (getenv \"EPROLOG\")))"
        $gfp12 = "ZmlsZV9nZXRfY29udGVudHMoJ2h0dHA6Ly9saWNlbnNlLm9wZW5jYXJ0LWFwaS5jb20vbGljZW5zZS5waHA/b3JkZXJ"

                $php_short = "<?" wide ascii
                $no_xml1 = "<?xml version" nocase wide ascii
        $no_xml2 = "<?xml-stylesheet" nocase wide ascii
        $no_asp1 = "<%@LANGUAGE" nocase wide ascii
        $no_asp2 = /<script language="(vb|jscript|c#)/ nocase wide ascii
        $no_pdf = "<?xpacket"

                        $php_new1 = /<\?=[^?]/ wide ascii
        $php_new2 = "<?php" nocase wide ascii
        $php_new3 = "<script language=\"php" nocase wide ascii

                        $cpayload1 = /\beval[\n\t ]{0,500}(\([^)]|\/\*)/ nocase wide ascii
        $cpayload2 = /\bexec[\n\t ]{0,500}(\([^)]|\/\*)/ nocase wide ascii
        $cpayload3 = /\bshell_exec[\n\t ]{0,500}(\([^)]|\/\*)/ nocase wide ascii
        $cpayload4 = /\bpassthru[\n\t ]{0,500}(\([^)]|\/\*)/ nocase wide ascii
        $cpayload5 = /\bsystem[\n\t ]{0,500}(\([^)]|\/\*)/ nocase wide ascii
        $cpayload6 = /\bpopen[\n\t ]{0,500}(\([^)]|\/\*)/ nocase wide ascii
        $cpayload7 = /\bproc_open[\n\t ]{0,500}(\([^)]|\/\*)/ nocase wide ascii
        $cpayload8 = /\bpcntl_exec[\n\t ]{0,500}(\([^)]|\/\*)/ nocase wide ascii
        $cpayload9 = /\bassert[\n\t ]{0,500}\([^)0]/ nocase wide ascii
        $cpayload10 = /\bpreg_replace[\n\t ]{0,500}\([^\)]{1,100}\/[ismxADSUXju]{0,11}(e|\\x65)/ nocase wide ascii
        $cpayload12 = /\bmb_ereg_replace[\t ]{0,500}\([^\)]{1,100}'e'/ nocase wide ascii
        $cpayload13 = /\bmb_eregi_replace[\t ]{0,500}\([^\)]{1,100}'e'/ nocase wide ascii
        $cpayload20 = /\bcreate_function[\n\t ]{0,500}(\([^)]|\/\*)/ nocase wide ascii
        $cpayload21 = /\bReflectionFunction[\n\t ]{0,500}(\([^)]|\/\*)/ nocase wide ascii
        $cpayload22 = /fetchall\(PDO::FETCH_FUNC[\n\t ]{0,500}[,}\)]/ nocase wide ascii

        $m_cpayload_preg_filter1 = /\bpreg_filter[\n\t ]{0,500}(\([^\)]|\/\*)/ nocase wide ascii
        $m_cpayload_preg_filter2 = "'|.*|e'" nocase wide ascii
        
    condition:
                filesize < 500 and not (
            any of ( $gfp* )
        )
        and (
            (
                (
                        $php_short in (0..100) or
                        $php_short in (filesize-1000..filesize)
                )
                and not any of ( $no_* )
            )
            or any of ( $php_new* )
        )
        and (
            any of ( $cpayload* ) or
        all of ( $m_cpayload_preg_filter* )
        )
        and
        ( ( #obf1 + #obf2 ) > 2 or #obf3 > 10 )
}

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

f13ddde3-91e3-469a-8a43-325220ea780f

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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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