What is stored cross-site scripting?
Cross-site Scripting (XSS) is a client-side code injection attack where an attacker can execute malicious scripts into a website or web application.
Stored cross-site scripting (often referred to as second-order or persistent XSS) arises when an application accepts data from an untrusted source and subsequently incorporates this data into its HTTP responses in an insecure manner.
Stored Cross-Site Scripting affects the web applications that allow users to store data. This action can potentially expose the users to this type of attack. There are many web applications that are vulnerable to Stored Cross-site Scripting.
These web applications fail to filter the stored inputs gathered from the users. As these stores that input in a data store for later use.
The Stored XSS attack can be successfully executed when a web application gathers malicious input from a user and then stores the input in a database for later use.
The main reason for a successful stored XSS attack is negligence by the developer. The developer had failed to filter the stored input properly.
Due to this negligence, malicious data will appear to be part of the web application and will run in the user’s browser using the web application’s privileges. As this vulnerability typically involves at least two requests to the application, it will also expose the user to second-order XSS.
The stored cross-site scripting vulnerability can be used to conduct several browser-based attacks including:-
Hijack an end user’s browser.
Steal sensitive information viewed by the application’s users.
Perform a pseudo defacement of the vulnerable application.
Port scanning of internal hosts (The internal hosts refer to the users of the application).
Direct the delivery of browser-based exploits.
A Stored XSS doesn’t require a malicious link to initiate. Successful exploitation can only be initiated when an end-user visits a page with a stored XSS vulnerability. The following are the phases that a typical site faces during a typical stored XSS attack scenario:-
The attacker will first store malicious code into the vulnerable web application’s page.
An end user will authenticate himself in the application.
After login, the user visits the web application’s vulnerable page.
The malicious code will get executed in the user’s browser.
Input stored by applications is usually used via HTML tags. The stored input can also be found as part of the application’s JavaScript content.
At this moment, it is crucial for the application to understand how the input is stored and how the input data is positioned in the context of the page.
Example
Let us consider the following input field is vulnerable to a stored XSS attack.
<input class="inputbox" type="text" name="email" size="40" value="example@beaglesecurity.com" />
The attacker will find ways to inject code into the vulnerable input box.
<input class="inputbox" type="text" name="email" size="40" value="example@beaglesecurity.com"> MALICIOUS CODE <!-- />
What are the impacts of stored cross-site scripting?
The impacts of stored cross-site scripting (XSS) vulnerabilities in web applications can be quite significant and detrimental. These vulnerabilities can lead to various security and user-related consequences, including:
1. Data theft
Attackers can exploit stored XSS to steal sensitive user data, such as login credentials, personal information, or financial details, which may be stored in the application.
2. Identity theft
Stolen user data can be used for identity theft or fraud, potentially causing financial and reputational damage to affected individuals.
3. Unauthorized access
Stored XSS can allow attackers to gain unauthorized access to user accounts, posing a security risk for both users and the application itself.
4. Data manipulation
Attackers can alter or delete data within the application, leading to data loss, corruption, or unauthorized changes to user-generated content.
5. Session hijacking
Exploiting stored XSS, attackers can hijack user sessions, giving them control overactive user accounts, leading to further malicious actions.
6. Malware distribution
Attackers can use stored XSS to deliver malicious payloads, such as malware or ransomware, to unsuspecting users, potentially causing system infections and data loss.
7. Phishing attacks
Stored XSS can be leveraged to display convincing phishing forms or login pages, tricking users into revealing their sensitive information.
8. Regulatory Violations
Depending on the nature of the exposed data and applicable data protection regulations, there may be legal consequences and financial penalties for non-compliance.
9. Business impact
Application downtime, data breaches, and the cost of incident response and recovery can have a direct financial impact on the organization.
10. Complex incident response
Responding to stored XSS incidents can be complex and resource-intensive, involving detection, remediation, user notifications, and regulatory compliance efforts.
Preventing and mitigating stored XSS vulnerabilities is essential to protect user data, maintain trust, and avoid legal and financial repercussions.
How can you prevent stored XSS vulnerabilities?
Preventing and mitigating stored cross-site scripting (XSS) vulnerabilities in web applications requires a combination of secure coding practices and ongoing security measures.
Here are steps to prevent and mitigate stored XSS vulnerabilities:
1. Input validation
Implement strict input validation on both client and server sides. Sanitize and validate user input to ensure it adheres to expected formats and does not contain malicious code.
2. Output encoding
Encode user-generated content and any data retrieved from untrusted sources before displaying it on web pages.
Use context-specific encoding methods, such as HTML encoding, to prevent script execution.
3. Content Security Policy (CSP)
Implement a CSP header in your web application. This security feature helps to control which scripts and resources are allowed to load, limiting the impact of XSS attacks.
4. Session management
Implement secure session management practices to prevent session fixation attacks, a common vector for XSS attacks.
5. Patch vulnerabilities
Regularly update your web application and third-party libraries to patch known vulnerabilities, including XSS issues.
6. Database escaping
When rendering user-generated content, use proper database escaping to prevent stored XSS. This is particularly important for dynamic content.
7. Regular scanning and testing
Conduct regular security scans and penetration testing to identify and remediate XSS vulnerabilities. Automated tools and manual testing can help uncover hidden issues.
8. HTTP-only Cookies
Mark cookies as HTTP-only to prevent JavaScript access, which can help mitigate the impact of XSS attacks.
9. Regular security training
Provide security training to development teams to raise awareness of secure coding practices and the significance of XSS prevention.
Preventing and mitigating stored XSS vulnerabilities is an ongoing effort that requires a combination of coding discipline, testing, and vigilance.
Staying informed about the latest security threats and vulnerabilities is essential to maintaining the security of your web application.
