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Summary of vulnerable functions in PHP

韦小宝

Mar 08, 2018 pm 05:41 PM

phpfunction

This article describes the existence of some PHP functions with small vulnerabilities in PHP. Those who have not understood the vulnerable functions in PHP can take a look at what to pay attention to when using these functions in actual PHP development. Let’s stop talking nonsense and read this article together!

1. Weak type comparison

##2.MD5 compare vulnerability

When PHP processes hash strings, if you use "!=" or "==" to Comparing hash values, it interprets each hash value starting with "0x" as the power of 0 in scientific notation (0), so if two different passwords are hashed, their hash value will be If the hash values all start with "0e", then PHP will think that they are the same.

Common payloads include

0x01 md5(str)
    QNKCDZO
    240610708
    s878926199a
    s155964671a
    s214587387a
    s214587387a
0x02 sha1(str)
    sha1(&#39;aaroZmOk&#39;)  
    sha1(&#39;aaK1STfY&#39;)
    sha1(&#39;aaO8zKZF&#39;)
    sha1(&#39;aa3OFF9m&#39;)

At the same time, MD5 cannot process arrays. If the following judgments are made, arrays can be used to bypass

if(@md5($_GET[&#39;a&#39;]) == @md5($_GET[&#39;b&#39;]))
{
    echo "yes";
}
//http://127.0.0.1/1.php?a[]=1&b[]=2

3.ereg function vulnerability :00 truncation

ereg ("^[a-zA-Z0-9]+$", $_GET[&#39;password&#39;]) === FALSE

String comparison analysis

Here if $_GET['password'] is an array, the return value is NULL
If it is 123 || asd || 12as || 123%00&&&**, the return value is true
The rest is false

4.What is $key?

Don’t forget that the program can extract the key of the variable itself as a variable and give it to the function for processing.

<?php
    print_r(@$_GET); 
    foreach ($_GET AS $key => $value)
    {
        print $key."\n";
    }
?>

5. Variable coverage

The main function involved is the extract function. Let’s look at an example

<?php  
    $auth = &#39;0&#39;;  
    // 这里可以覆盖$auth的变量值
    print_r($_GET);
    echo "</br>";
    extract($_GET); 
    if($auth == 1){  
        echo "private!";  
    } else{  
        echo "public!";  
    }  
?>

extract can receive an array and then give it again Variable assignment, procedure page is very simple.

at the same time! PHP's feature $ can be used to assign variable names and can also cause variable overwriting!

<?php  
    $a=&#39;hi&#39;;
    foreach($_GET as $key => $value) {
        echo $key."</br>".$value;
        $$key = $value;
    }
    print "</br>".$a;
?>

Construction

http://127.0.0.1:8080/test.php?a=12 can achieve the purpose.

6.strcmp

如果 str1 小于 str2 返回  0；如果两者相等，返回 0。 
先将两个参数先转换成string类型。 
当比较数组和字符串的时候，返回是0。 
如果参数不是string类型，直接return

<?php
    $password=$_GET[&#39;password&#39;];
    if (strcmp(&#39;xd&#39;,$password)) {
     echo &#39;NO!&#39;;
    } else{
        echo &#39;YES!&#39;;
    }
?>

Construction

http://127.0.0.1:8080/test.php?password[]=

7.is_numeric

Needless to say:

<?php
echo is_numeric(233333);       # 1
echo is_numeric(&#39;233333&#39;);    # 1
echo is_numeric(0x233333);    # 1
echo is_numeric(&#39;0x233333&#39;);   # 1
echo is_numeric(&#39;233333abc&#39;);  # 0
?>

8.preg_match

If in progress Regular expressionWhen matching, if there is no restriction on the beginning and end of the string (^ and $), there may be bypass problems

<?php
$ip = &#39;asd 1.1.1.1 abcd&#39;; // 可以绕过
if(!preg_match("/(\d+)\.(\d+)\.(\d+)\.(\d+)/",$ip)) {
  die(&#39;error&#39;);
} else {
   echo(&#39;key...&#39;);
}
?>

9.parse_str

Similar functions to parse_str() include mb_parse_str(). parse_str parses the string into multiple variables. If the parameter str is the query string passed in by the URL, then It is resolved to a variable and set to the current scope.

A type of time variable coverage

<?php
    $var=&#39;init&#39;;  
    print $var."</br>";
    parse_str($_SERVER[&#39;QUERY_STRING&#39;]);  
    echo $_SERVER[&#39;QUERY_STRING&#39;]."</br>";
    print $var;
?>

10.String comparison

<?php  
    echo 0 == &#39;a&#39; ;// a 转换为数字为 0    重点注意
    // 0x 开头会被当成16进制54975581388的16进制为 0xccccccccc
    // 十六进制与整数，被转换为同一进制比较
    &#39;0xccccccccc&#39; == &#39;54975581388&#39; ;

    // 字符串在与数字比较前会自动转换为数字，如果不能转换为数字会变成0
    1 == &#39;1&#39;;
    1 == &#39;01&#39;;
    10 == &#39;1e1&#39;;
    &#39;100&#39; == &#39;1e2&#39; ;    

    // 十六进制数与带空格十六进制数，被转换为十六进制整数
    &#39;0xABCdef&#39;  == &#39;     0xABCdef&#39;;
    echo &#39;0010e2&#39; == &#39;1e3&#39;;
    // 0e 开头会被当成数字，又是等于 0*10^xxx=0
    // 如果 md5 是以 0e 开头，在做比较的时候，可以用这种方法绕过
    &#39;0e509367213418206700842008763514&#39; == &#39;0e481036490867661113260034900752&#39;;
    &#39;0e481036490867661113260034900752&#39; == &#39;0&#39; ;

    var_dump(md5(&#39;240610708&#39;) == md5(&#39;QNKCDZO&#39;));
    var_dump(md5(&#39;aabg7XSs&#39;) == md5(&#39;aabC9RqS&#39;));
    var_dump(sha1(&#39;aaroZmOk&#39;) == sha1(&#39;aaK1STfY&#39;));
    var_dump(sha1(&#39;aaO8zKZF&#39;) == sha1(&#39;aa3OFF9m&#39;));
?>

11.unset

unset(bar); is used to destroy the specified variable. If the variable bar is included in the

request parameters, some variables may be destroyed to bypass the program logic.

<?php  
$_CONFIG[&#39;extraSecure&#39;] = true;

foreach(array(&#39;_GET&#39;,&#39;_POST&#39;) as $method) {
    foreach($$method as $key=>$value) {
      // $key == _CONFIG
      // $$key == $_CONFIG
      // 这个函数会把 $_CONFIG 变量销毁
      unset($$key);
    }
}

if ($_CONFIG[&#39;extraSecure&#39;] == false) {
    echo &#39;flag {****}&#39;;
}
?>

12.intval()

int to string:

$var = 5;  
方式1：$item = (string)$var;  
方式2：$item = strval($var);

string to int: intval() function.

var_dump(intval(&#39;2&#39;)) //2  
var_dump(intval(&#39;3abcd&#39;)) //3  
var_dump(intval(&#39;abcd&#39;)) //0 
// 可以使用字符串-0转换，来自于wechall的方法

Explains that when converting intval(), it will convert from the beginning of the string until it encounters a non-numeric character. Even if a string that cannot be converted appears, intval() will not report an error but return 0

By the way, intval can be truncated by %00

if($req[&#39;number&#39;]!=strval(intval($req[&#39;number&#39;]))){
     $info = "number must be equal to it&#39;s integer!! ";  
}

If $req['number']=0% 00 can bypass

13.switch()

If switch is a case of numeric type, switch will convert the parameters into int type. The effect is equivalent to the intval function. As follows:

<?php
    $i ="abc";  
    switch ($i) {  
    case 0:  
    case 1:  
    case 2:  
    echo "i is less than 3 but not negative";  
    break;  
    case 3:  
    echo "i is 3";  
    } 
?>

14.in_array()

$array=[0,1,2,&#39;3&#39;];  
var_dump(in_array(&#39;abc&#39;, $array)); //true  
var_dump(in_array(&#39;1bc&#39;, $array)); //true

Entering a string in any place where PHP considers it to be an int will be

forced conversion

15.serialize and unserialize vulnerabilities

这里我们先简单介绍一下php中的魔术方法（这里如果对于类、对象、方法不熟的先去学学吧），即Magic方法，php类可能会包含一些特殊的函数叫magic函数，magic函数命名是以符号开头的，比如 construct， destruct，toString，sleep，wakeup等等。这些函数都会在某些特殊时候被自动调用。 
例如construct()方法会在一个对象被创建时自动调用，对应的destruct则会在一个对象被销毁时调用等等。 
这里有两个比较特别的Magic方法，sleep 方法会在一个对象被序列化的时候调用。 wakeup方法会在一个对象被反序列化的时候调用。

<?php
class test
{
    public $username = &#39;&#39;;
    public $password = &#39;&#39;;
    public $file = &#39;&#39;;
    public function out(){
        echo "username: ".$this->username."<br>"."password: ".$this->password ;
    }
     public function toString() {
        return file_get_contents($this->file);
    }
}
$a = new test();
$a->file = &#39;C:\Users\YZ\Desktop\plan.txt&#39;;
echo serialize($a);
?>
//tostring方法会在输出实例的时候执行，如果实例路径是隐秘文件就可以读取了

echo unserialize triggers the tostring function, and the C:\Users\YZ\Desktop\plan.txt file can be read below

<?php
class test
{
    public $username = &#39;&#39;;
    public $password = &#39;&#39;;
    public $file = &#39;&#39;;
    public function out(){
        echo "username: ".$this->username."<br>"."password: ".$this->password ;
    }
     public function toString() {
        return file_get_contents($this->file);
    }
}
$a = &#39;O:4:"test":3:{s:8:"username";s:0:"";s:8:"password";s:0:"";s:4:"file";s:28:"C:\Users\YZ\Desktop\plan.txt";}&#39;;
echo unserialize($a);
?>

16.session deserialization vulnerability

The main reason is

ini_set('session.serialize_handler', 'php_serialize');
ini_set( 'session.serialize_handler', 'php');
The two methods of handling sessions are different
I don't understand this thing very well, I will write a solution later!
There is a question here! This is a
topic

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The basic structure of PHP functions

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