What is a CSP error?

A CSP error, or Content Security Policy error, occurs in web browsers when a website violates the rules set by the website's own Content Security Policy. CSP is a security mechanism that helps to prevent Cross-Site Scripting (XSS) and other types of code injection attacks. It works by defining a set of rules that tell the browser what sources of content (like scripts, styles, images, etc.) are considered valid for a given webpage.

When a browser encounters a resource that violates the CSP defined by a website, it will block the resource from loading and report a CSP error. For example, if a website has a CSP that disallows the execution of inline JavaScript, and the HTML includes a <script> tag with JavaScript code directly within it, the browser will block the execution of this script and display a CSP error. These errors are usually visible in the browser's developer console.

CSP errors can be caused by various issues such as: improperly configured CSP headers or meta tags, attempts to load resources from untrusted domains, usage of inline JavaScript or CSS when it's disallowed by the CSP, use of eval() or similar unsafe JavaScript constructs and also the use of outdated or deprecated browser features. Diagnosing and resolving CSP errors typically involves examining the specific error message in the browser console, reviewing the website's CSP, and adjusting the website's code or CSP configuration to comply with the defined policies. Properly implemented CSP significantly enhances the security of a website.

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