Content Security Policy (CSP) is a computer security standard designed to prevent cross-site scripting (XSS), clickjacking, and other code injection attacks by controlling the types of content that a web page can load. It is implemented as an HTTP header that specifies the allowed sources for various content types, such as scripts, stylesheets, images, and fonts.
Violation Reporting
When a CSP violation occurs, the browser sends a violation report to a specified endpoint. The report contains information such as the blocked URI (the source of the violation), the violated directive, the document URI, and the original policy. This information can be used to identify the cause of the violation and take appropriate action to prevent future violations.
Blocked URI
The blocked URI in the violation report indicates the source of the content that violated the CSP policy. It can be a full path or just the origin of the resource, depending on the browser implementation. For example, if a page attempts to load a script from an unauthorized domain, the blocked URI in the violation report would be the full path to the script.
Preventing Information Leakage
In some cases, the browser may only include the origin of the violating resource in the violation report, rather than the full path. This is done to prevent sensitive information about cross-origin resources from being leaked. For example, if a page attempts to load a script from a cross-origin domain that contains sensitive information, the browser would only include the origin of the script in the violation report, not the full path.
Conclusion
CSP violations are a valuable tool for identifying and preventing security vulnerabilities in web applications. By understanding the causes of CSP violations and taking appropriate action to address them, developers can help to protect their applications from attack.
References
- Content Security Policy (CSP) – HTTP | MDN (https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP)
- Content Security Policy – Wikipedia (https://en.wikipedia.org/wiki/Content_Security_Policy)
- Automatically detect potential frontend attacks that cause Content Security Policy (CSP) violations | Dynatrace (https://www.dynatrace.com/news/blog/automatically-detect-potential-frontend-attacks-that-cause-content-security-policy-csp-violations/)
FAQs
What is a CSP violation?
A CSP violation occurs when a web page attempts to load content from a source that is not allowed by the page’s Content Security Policy (CSP). CSP is a security standard that helps to prevent attacks such as cross-site scripting (XSS) and clickjacking.
What information is included in a CSP violation report?
A CSP violation report typically includes the following information:
* Blocked URI: The source of the content that violated the CSP policy.
* Violated directive: The CSP directive that was violated.
* Document URI: The URI of the document that attempted to load the blocked content.
* Original policy: The CSP policy that was in effect at the time of the violation.
How can I prevent CSP violations?
There are a number of ways to prevent CSP violations, including:
* Use a CSP that is appropriate for your website’s needs.
* Ensure that all of your website’s resources are loaded from allowed sources.
* Use a CSP monitoring tool to identify and fix CSP violations.
What should I do if I receive a CSP violation report?
If you receive a CSP violation report, you should investigate the cause of the violation and take appropriate action to prevent future violations. This may involve updating your CSP policy, fixing any vulnerabilities in your code, or contacting the provider of the blocked content.
Why might the blocked URI in a CSP violation report be truncated?
In some cases, the browser may only include the origin of the violating resource in the violation report, rather than the full path. This is done to prevent sensitive information about cross-origin resources from being leaked.
What are some common causes of CSP violations?
Some common causes of CSP violations include:
* Loading resources from unauthorized domains.
* Using inline scripts or styles.
* Using third-party libraries or plugins that are not CSP-compliant.
* Misconfiguring the CSP policy.
How can I test my CSP policy for violations?
There are a number of tools available for testing CSP policies for violations. These tools can help you to identify any potential vulnerabilities in your policy before it is deployed to a production environment.