Stored HTML injection, also known as persistent HTML injection, is a type of web application vulnerability that allows an attacker to inject malicious HTML code into a web application's database or other storage mechanism. This injected HTML code is then retrieved and displayed to other users of the application, potentially leading to various security risks.
Unlike other types of HTML injection attacks, such as reflected or DOM-based injection, where the injected code is only temporarily stored and executed on the client-side, stored HTML injection involves the long-term storage of the injected code on the server-side. This makes it particularly dangerous as the injected code can impact multiple users and persist even after the attacker has left the site.
The process of exploiting a stored HTML injection vulnerability typically involves the following steps:
1. Identifying the vulnerability: The attacker first identifies a web application that is vulnerable to stored HTML injection. This can be done through manual inspection or by using automated scanning tools.
2. Crafting the payload: The attacker then creates a payload containing malicious HTML code that will be injected into the application's storage mechanism. The payload is designed to exploit the vulnerability and achieve the attacker's objectives, such as stealing sensitive information or performing unauthorized actions.
3. Injecting the payload: The attacker submits the payload through a vulnerable input field, such as a comment box or a user profile form. The application stores the payload in its database or other storage mechanism without proper sanitization or validation.
4. Retrieving and executing the payload: When the stored payload is retrieved and displayed to other users, the web application fails to properly sanitize or escape the injected HTML code, causing it to be rendered as part of the page content. This allows the attacker's code to execute in the context of other users' browsers, potentially leading to various attacks, such as cross-site scripting (XSS), phishing, or defacement.
The impact of a successful stored HTML injection attack can be severe. It can allow an attacker to steal sensitive information, such as login credentials or personal data, manipulate the content of the web application, or even gain unauthorized access to the underlying server or infrastructure.
To prevent stored HTML injection attacks, web application developers should follow secure coding practices, including:
1. Input validation and sanitization: All user-supplied input should be properly validated and sanitized before being stored or displayed. This includes implementing server-side input validation and using output encoding techniques, such as HTML entity encoding or Content Security Policy (CSP), to prevent the execution of injected code.
2. Parameterized queries or prepared statements: When interacting with databases, developers should use parameterized queries or prepared statements to prevent SQL injection attacks, which can also be used as a vector for stored HTML injection.
3. Content security policies: Implementing a robust content security policy can help mitigate the impact of stored HTML injection attacks by restricting the types of content that can be loaded or executed on a web page.
4. Regular security testing: Regularly conducting security assessments, such as penetration testing or code reviews, can help identify and remediate stored HTML injection vulnerabilities before they can be exploited by attackers.
Stored HTML injection is a critical web application vulnerability that allows attackers to inject malicious HTML code into a web application's storage mechanism. It differs from other types of HTML injection attacks in that the injected code is stored on the server-side and can impact multiple users. Preventing stored HTML injection requires secure coding practices, including input validation, output encoding, parameterized queries, content security policies, and regular security testing.
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