Content Security Policy

What is Content Security Policy?

Content Security Policy (CSP) is a security measure developed by the Mozilla Foundation to prevent attacks by infiltrating data into websites. This measure defines rules and regulations that determine which content and scripts may be executed on a website. A central aim of CSP is to prevent access by active code such as JavaScript to content from other sources, thereby increasing the security of the website and preserving the integrity of the data.

Technically speaking, CSP is implemented by inserting specific directives into the HTTP header of a website or by using an element in the HTML document. These directives determine which sources for scripts, Stylesheetsimages and other resources are permitted. For example, directives such as script-src 'self' can be used to allow only custom scripts, while style-src 'self' loading external Stylesheets forbidden.

The use of CSP offers several security advantages. In particular, it minimizes the risk of cross-site scripting (XSS) attacks, in which attackers inject malicious code into a website. The strict separation of HTML code and external code effectively makes it more difficult to inject and execute unwanted scripts. In addition, CSP can help to reduce the risk of packet sniffing by only allowing secure web protocols such as HTTPS.

Main tasks and protective measures

The main task of the Content Security Policy (CSP) is to protect websites from attacks by malicious code. Important protective measures are taken to prevent external code from accessing or executing the content of a website. CSP ensures that the HTML code of the website is strictly separated from external code in order to close security gaps and minimize the attack surface.

One of the central protective measures is the creation and enforcement of various rules for loading scripts. By using specific directives such as script-src for JavaScript and style-src for Stylesheets can be used to determine exactly which resources may be loaded from which sources. These policies can be configured to only allow self-hosted content ('self') or trusted domains.

In addition, CSP relies on the containment of packet sniffing through regulations that specify the use of secure web protocols, ideally only HTTPS. This increases data security and prevents sensitive information from being intercepted. Example values for directives include 'none' for blocking all sources, 'self' for your own domain, unsafe-inline for inline scripts (although this should be avoided), and nonce-{random}to execute only temporarily permitted scripts.

Proper use of CSP not only improves security, but also user safety by reducing the likelihood of cross-site scripting (XSS) and other code injection attacks. These safeguards are critical to preserving the integrity of websites and ensuring a secure user experience.

Implementation and examples

The Implementation from Content Security Policy (CSP) can be done in various ways, depending on the desired configuration method and the structure of the website. A common method is to insert CSP directives in the HTTP header of the website. These are aimed at the web server to determine which content may be loaded and executed.

HTTP headers and examples

A typical example of an HTTP header entry would be:

Content-Security-Policy: default-src 'self'

This entry only allows content from your own domain. If you also want to load scripts from a trusted external source, the header could look like this:

Content-Security-Policy: default-src 'self'; script-src 'self' *.vertrauenswürdigeseite.com

For applications that only use secure connections, an entry can be defined as follows:

Content security policy: default-src https://onlinebanking.meineseite.com

Another method of implementing CSP is to use a <meta>-element in the HTML document. Although this method serves as a fallback if the server does not send CSP headers, server headers always take precedence. An example of an element would be:

<meta http-equiv=”Content-Security-Policy” content=”default-src ‘self'”>

Server-side scripting languages and web server configuration

A CSP header can also be set in server-side scripting languages such as PHP. A simple PHP script could look like this, for example:

<?php

header("Content-Security-Policy: default-src 'self'; script-src 'self'");

?>

The web server configuration also offers options for implementing CSP. In Apache or Nginx servers, CSP can be defined directly in the server configuration. For example, a CSP policy can be added in an Apache server configuration:

Header set Content-Security-Policy "default-src 'self'"

The correct application of all these methods can ensure effective Content Security Policy which significantly improves the security and integrity of the website.

Versions and further development

The Versions the Content Security Policy (CSP) have evolved since their introduction to meet the growing demands of internet security. Each new version brings enhanced features and additional protection measures to counter modern threats and attack methods.

CSP Version 1.0

The first version of CSP, known as CSP 1.0, was introduced by the Mozilla Foundation and provided basic security mechanisms to prevent the execution of untrusted code on websites. This version laid the foundation for policy-based security and enabled the definition of trusted sources for scripts and other content.

CSP Version 2.0

The current version is CSP 2.0, which brings numerous improvements and extended functions. CSP 2.0 added additional directives to enable even more granular controls. These include specific directives such as base-uri, child-src and form-actionwhich make it possible to further increase security and better defend against specific attack scenarios. This version also extended the reporting functionalities so that policy violations can be logged.

CSP Version 3.0

CSP 3.0 is currently under development and promises further innovations and improvements. This version is expected to introduce additional directives and controls to ensure protection against more complex and sophisticated attacks. Improvements in the handling of content in modern web applications and optimizations for easier implementation are the focus of this version.

The continuous further development of the Content Security Policy demonstrates the ongoing effort to improve web security and protect against new threats. Developers and security experts are working tirelessly on these guidelines to make the Internet experience safer.

Safety mechanisms and recommendations

The various Security mechanisms and recommendations made in the Content Security Policy (CSP) aim to improve the security of web applications and minimize the risk of cyberattacks. An important recommendation is to avoid using eval() and functions such as setTimeout()/setInterval() with strings as code parameters, as these techniques are susceptible to code injection.

Modern alternatives and HTTPS

Instead, modern Browser safer alternatives that prevent the execution of malicious code. Another mechanism is the avoidance of inlineJavaScript in HTML attributes. Instead of defining events directly in the HTML code, external event listeners are recommended. This not only makes the code more secure, but also more maintainable and clearer.

The use of HTTPS for all components of a website can also be enforced using CSP directives. Through specifications such as upgrade-insecure-requests ensures that all non-encrypted requests are automatically switched to HTTPS. This measure protects the data during transmission and prevents it from being intercepted by third parties.

Reports and continuous review

Another important aspect is the continuous monitoring and reporting of CSP violations. It is recommended to configure the enforced CSP header to log potential violations. These reports can then be used to identify and close security gaps. Tools and services for checking the CSP can help to identify vulnerabilities at an early stage and take appropriate action.

In summary, the safety mechanisms and recommendations associated with the Content Security Policy This provides a strong basis for defense against various types of attacks. The ongoing development and adaptation of these guidelines in collaboration with browser manufacturers and web standards development bodies ensures that new threats can be effectively defended against.