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Content security policy

Content security policy

(also CSP)

Content security policy definition

Content security policy (CSP) is a security standard that web developers implement to prevent certain types of security breaches, such as cross-site scripting (XSS) and data injection attacks. By setting CSP directives in HTTP headers, developers specify the domains a browser should consider as good sources of executable scripts, thus limiting the potential damage from injected malicious content.

See also: SSL encryption

Content security policy examples

  • Whitelisting sources: With CSP, developers can whitelist trusted sources of content, such as scripts, images, or stylesheets. For example, a directive like default-src ‘self’ allows only content hosted on the same origin as the web page.
  • Blocking inline scripts: A common use of CSP is to disallow inline scripts, reducing the risk of XSS attacks.

Advantages and disadvantages of content security policy


  • Security enhancement: CSP provides an added layer of security that helps to detect and mitigate certain types of attacks, such as XSS and data injection attacks.
  • Flexible source definitions: Developers have the flexibility to define valid sources at a granular level for different types of content separately.


  • Implementation complexity: Setting up an effective CSP can be complex because it requires defining specific policies for each type of content.
  • Potential for over-blocking: If not carefully configured, CSP can block legitimate content, affecting website functionality.

Using content security policy

  • Developers should define CSP directives according to the specific needs of their website, ensuring legitimate sources of content are whitelisted, and potential malicious sources are blocked.
  • Test CSP policies thoroughly before deployment to avoid unintentional blocking of legitimate content.
  • Use tools like content security policy report-only mode and CSP Evaluator to test and refine your CSP implementation.

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