Content security policy definition

Content security policy

(also CSP)

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

Pros:

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.

Cons:

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.