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Understanding Stored XSS

Web SecurityXSSInput ValidationOutput EscapingDefense in Depth

Stored XSS, also known as Persistent XSS, is a critical web application security vulnerability. It occurs when an application stores user-supplied input and later embeds it in web pages served to other users without proper sanitization or escaping. This can lead to malicious scripts being executed in the context of the victim's browser.

Key Points

  • Stored XSS occurs when user input is stored and later displayed without proper sanitization.
  • Common examples include web forum posts, product reviews, and user comments.
  • Mitigations include validating and sanitizing input, using output escaping, and applying context-specific encoding.

Examples

Stored XSS can be found in various web applications where user input is stored and later displayed. Some common examples include:

  • Web forum posts
  • Product reviews
  • User comments

For a detailed example, you can refer to this article.

Mitigations

To protect against Stored XSS, consider the following best practices:

  • Validate and sanitize input: Ensure that all user input is properly validated and sanitized before storing it.
  • Use output escaping: Escape any user-supplied data before embedding it in web pages.
  • Apply context-specific encoding: Use appropriate encoding techniques based on the context in which the data is used.
  • Practice defense in depth: Do not rely solely on client-side validation; implement multiple layers of security.

Learn More

For more information on XSS vulnerabilities and how to mitigate them, consider exploring the following resources: