Cross-Site Scripting in SvelteKit Prerendered Pages

Executive Summary

This vulnerability is a cross-site scripting (XSS) flaw in SvelteKit versions before 3.0.0. It occurs in prerendered pages when the cache-control header value, set via setHeaders from an untrusted source, is inserted without escaping into a meta tag. Attackers can inject malicious HTML or JavaScript by manipulating this value during prerendering, which executes when users visit the page.

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Detection Guidance

To detect this vulnerability, check if your SvelteKit application uses versions before 3.0.0 and prerenders pages with setHeaders for cache-control. Inspect the HTML output of prerendered pages for unescaped cache-control meta tags. Use commands like grep to search for setHeaders usage in your codebase.

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Impact Analysis

An attacker could exploit this to inject and execute malicious scripts in the context of a user's browser session. This could lead to theft of session cookies, sensitive data exposure, or unauthorized actions performed on behalf of the user. The impact depends on the privileges of the affected user and the nature of the injected payload.

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Compliance Impact

This XSS vulnerability could lead to unauthorized data access or modification, violating GDPR's integrity and confidentiality principles or HIPAA's safeguards for protected health information. Organizations may face compliance violations if user data is compromised due to this flaw.

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Mitigation Strategies

Upgrade SvelteKit to version 3.0.0 or later. If upgrading is not immediately possible, avoid using setHeaders to forward untrusted cache-control header values on prerendered pages. Use a fixed, trusted cache policy instead.

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