On the Security of PHP

Last Updated: April 18, 2021

PHP has maintained a relatively stable presence on the internet over the past few years, and its popularity as a scripting language is only getting bigger. It is best known for providing interfaces between an internet user and a host.

PHP scripts can be vulnerable to cyber-attacks, and despite the fact that it is coded with security in mind, knowing the risks involved is really important when eradicating any compromises to the security side of things.  In the article below, we will talk about the different security issues found with PHP, and how to secure it.

Intro

PHP, otherwise known as ‘PHP Hypertext Preprocessor’, is a scripting language on the server side of things that helps create dynamic webpages, by embedding the relevant code into HTML documents. It combines feature that you will find with computer programs like Perl and Java and includes its own elements as well, so that you get power and flexibility when you are creating webpages according to your content.

Just like with any other tool out there, it comes with its dangers and risks. When you are aware of these risks, you can lower the chances of the security of your PHP code being compromised in any way.

Just keep in mind, though, that the guidelines below only highlight some practices that can be used to reduce risk. This definitely isn’t completely comprehensive, and you should see the idea of security in general as an evolving process that is always changing. Below is the basis to understanding security risks involved with PHP.

The Source of Security Breaches

PHP can be operated either as a web server module, or CGI application. Regardless of how it is run, it can access every part of the host, including the interfaces and file system.

This means that it does have the potential to do a lot of damage. In order to prevent any damage or attacks, the developer needs to know everything that can go wrong. This is a job in itself. Knowing the weaknesses of a system is important, but can be complicated.

Trusting User Input

One of the biggest sources of vulnerability is user input. There are many scripts that use information provided by a user in a web form, and the way that the script processes this information can vary. If user input is taken at face value, then the user has the power to attack the script, as well as the hosting platform.

Additionally, PHP takes note of environment variables that are accessible by name anywhere within the script. This means that you can just look at $HOSTNAME and $PATH for information.

The issue with external variables is that you have no way of knowing whether the data is authentic or not. Second, because PHP wants to make everything available everywhere, no variable can technically be trusted, whether it is coming from the outside of the inside. Take the following example:

$tempfile = “12345.tmp”;

 …
 # do something with $tempfile here
 # and some form processing
 …

 unlink ($tempfile);

If you handle this safely before you unlink it, then the last statement can still pose a risk. A hacker can create their own form containing a similar field to:

<input type=hidden name="tempfile"
     value="../../../etc/passwd">

PHP will include the field name in the global namespace for all to see, and overwrite the original variable.

Trusting Environment Variables

The script itself doesn’t have control over what is included in environment variables when it begins to look for a certain prompt. This means that a hacker can easily modify the path to a certain point, with a malware version of the program. This is an easy way for hackers to get in.

There are some sites that will restrict access based on the link that you are trying to access the site from. They use a specific variable to achieve this. The bottom line here is that environmental variables can’t be trusted. Hackers can easily exploit some of the software that runs on the PHP server to gain access. As a result, the PHP script that relies on those variables is no longer secure and safe from being infiltrated.

When it comes to thinking about security, environment variables and user input data are one and the same. This is because they could all be fronting data that is from an unknown origin, therefore making it risky. This is why it should be filtered and examined as often as possible.

Database Interactions

PHP makes it really easy to interact with a lot of different databases out there, especially from within the script. However, this also poses a security issue. A lot of the time PHP use input from a web form.

Luckily, you can adjust the script privileges, in order to minimize the damage that can be done to the database, but the trouble here is that a lot of the time this isn’t enough to resolve the issue completely, as the user can still implement queries that will extract specific information. Therefore, if user input needs to be entered into the database, it should be filtered and examined for dangerous code.

Weak Spots in the Interpreter

PHP as a program has a few security vulnerabilities along different stages of its coding. Some versions have proven vulnerable to format string attacks in the logging part of the function, as an example.

The issue is that PHP passes the log message along to those functions, and the log message has every chance of containing input from a user. Therefore, a hacker can easily make the most of this to compromise the servers of PHP that continue to run the risky code, unless the server has disabled PHP login because of warnings and errors.

Hosts that run PHP need to be aware of the risks, and understand that there are still ways for the software to be infiltrated, based on how it is coded and set up to run.

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