Complete explanation of PHP vulnerabilities (2) - command injection attack.

Command injection attack

The following 5 functions can be used in PHP to execute external applications or functions

system, exec, passthru, shell_exec, "(same function as shell_exec)

Function prototype

string system(string command , int &return_var)

command The command to be executed

return_var stores the status value after execution of the execution command

string exec (string command, array &output, int &return_var)

command The command to be executed

output Get the execution command Each line of string output

Return_var stores the status value after executing the command

void passthru (string command, int &return_var)

command The command to be executed

return_var stores the status value after executing the command

string shell_exec (string command)

command command to be executed

Vulnerability example

Example 1:

命令注入攻击
PHP中可以使用下列5个函数来执行外部的应用程序或函数
system、exec、passthru、shell_exec、“(与shell_exec功能相同)
函数原型
string system(string command, int &return_var)
    command 要执行的命令
    return_var 存放执行命令的执行后的状态值
string exec (string command, array &output, int &return_var)
    command 要执行的命令
    output 获得执行命令输出的每一行字符串
    return_var 存放执行命令后的状态值
void passthru (string command, int &return_var)
    command 要执行的命令
    return_var 存放执行命令后的状态值
    string shell_exec (string command)
    command 要执行的命令
漏洞实例
例1:

We submit http://www.sectop.com/ex1.php?dir=| cat /etc/passwd

After submission, The command becomes system("ls -al | cat /etc/passwd");

eval injection attack

eval function executes the input string parameters as PHP program code

function Prototype:

mixed eval(string code_str) //eval injection usually occurs when the attacker can control the input string

When we submit http://www.sectop.com/ex2.php?arg=phpinfo( ); The vulnerability arises;

dynamic function

php
func A()
{
dosomething();
}
func B()
{
dosomething();
}
if (isset( $_GET["func"]))
{
$myfunc = $_GET["func"];
echo $myfunc();
}
?>

The programmer originally wanted to dynamically call A and B function, then we submit http://www.sectop.com/ex.php?func=phpinfo vulnerability generation

Prevention methods

1. Try not to execute external commands

2. Use custom functions or function libraries to Function to replace external commands

3. Use escapeshellarg function to process command parameters

4. Use safe_mode_exec_dir to specify the path of the executable file

esacpeshellarg function will escape any characters that cause the end of parameters or commands, single quotes "'" , replace with "'", double quotes """, replace with """, replace semicolon ";" with ";"

Use safe_mode_exec_dir to specify the path of the executable file. You can put the commands you will use here in advance. Within the path

safe_mode = On

safe_mode_exec_dir = /usr/local/php/bin/

The above is the complete solution to PHP vulnerabilities (2) - command injection attack. For more related content, please pay attention to the PHP Chinese website (www. php.cn)!