Detailed explanation of PHP security configuration under lnmp (disabling unsafe PHP functions and separating PHP uploads, etc.)

Several aspects of php security configuration:

1. Use open_basedir to limit virtual host cross-directory access

Instructions: The PHP program under www.xingzuo51.com is limited to the two directories configured by open_basedir, and cannot access other directories. If the above configuration is not done, the programs of test.xingzuo51.com and www.xingzuo51.com can access each other. If one of the sites has a vulnerability and a hacker has implanted a webshell, you can use this site to take down other sites on the same server and finally install a Trojan horse.

Note: The directory must be appended with / at the end. For example, if you write /tmp, the site also has /tmp123 and other directories starting with /tmp, then hackers can also access these directories. In addition, php5.3 and above support this writing method, but 5.2 does not.

2. Disable unsafe PHP functions disable_functions = show_source,system,shell_exec,passthru,exec,popen,proc_open,proc_get_status,phpinfo PHP is prohibited from executing the above PHP functions. The above PHP programs can execute Linux commands, such as ping, netstat, mysql, etc. If your system has a privilege escalation bug, you will know the consequences.

3. Pay attention to software security information Actively pay attention to the Linux kernel, PHP security and other information and take timely action on errors

4. PHP users can read only This method is my most recommended method, but you must discuss it with the PHP engineer before executing it. Why? For example, the user and group in the root directory of the site www.xingzuo51.com are nobody, and the user and group running php are phpuser. The directory permissions are 755 and the file permissions are 644. In this way, php is read-only and cannot write any files to the site directory. In other words, users cannot upload files. Even if there are loopholes, hackers cannot pass the backdoor, let alone install Trojans. Before doing this, tell the programmer to change the file cache to NoSQL memory cache (such as memcached, redis, etc.), and the uploaded files will pass through The interface is passed to other servers (static servers). Note: It is a very bad habit to program to generate local cache. Using file cache is slow and wastes disk space. The most important thing is that the server cannot scale horizontally under normal circumstances

5. Close php error log

Once an error occurs in the program, detailed error information will be immediately displayed to the user, including the path, and sometimes even the database account password. Injection and penetration passwords are basically guessed through this error report. Strongly turn it off in production environments

6. PHP upload separation Upload files to remote server such as nfs etc. Of course, you can also call the PHP interface you wrote. Even if there is an upload vulnerability, the file will be transferred to the static server. Trojan horses and other files cannot be executed at all.

Example: php site www.xingzuo51.com, directory/data/site/www.xingzuo51.com Static file site static.xingzuo51.com, directory/data/site/static.xingzuo51.com The file was directly transferred to /data/site/static.xingzuo51.com. The uploaded file cannot be accessed through www.xingzuo51.com. It can only be accessed through static.xingzuo51.com, but static.xingzuo51.com does not support php.

7. Close php information

Do not disclose your PHP version information easily to prevent hackers from launching attacks against this version of PHP.

8. Disable dynamic loading of link libraries

9. Disable opening remote url

In fact, this is not really safe and will not lead to problems such as web intrusion. However, this greatly affects performance. The author believes that it is a security issue in a narrow sense.

The following methods will not be able to obtain the remote url content

Get local file content:

If the site traffic is not large and the database is running well, but the web server load is surprisingly high, please check directly to see if this method is available.

php obtains the content of the remote web, it is recommended to use curl.