Cross-Site Scripting (XSS)
Cross-site scripting (XSS) is a class of vulnerabilities where attackers inject malicious JavaScript into pages other users view. Injected script runs in the victim browser with access to that origin, enabling theft of cookies, tokens, and private API responses.
Technical Architecture & Deep-Dive
Stored XSS persists dangerous payloads in databases, such as comment fields rendered without encoding. Reflected XSS bounces input through URLs or error pages. DOM-based XSS manipulates client-side JavaScript that writes untrusted data into the document.
XSS is especially dangerous for SPAs that hold API tokens in memory or localStorage. Content Security Policy limits script sources, strict output encoding neutralizes HTML contexts, and routing third-party calls through an edge proxy shrinks the connect-src surface attackers can abuse for exfiltration.
Key Architectural Benefits
Implement Cross-Site Scripting (XSS) at the Edge
Deploy lightweight API aggregation, edge caching, and secret injection in minutes without Docker containers or complex servers.
Frequently Asked Questions
Q:Can an edge proxy prevent XSS in my React app?
An edge proxy cannot fix unsafe rendering in your UI, but it can reduce blast radius by keeping upstream secrets off the client and constraining where scripts may send stolen data.
Related Architecture Concepts
Content Security Policy (CSP) is an HTTP response header that tells browsers which sources of scripts, styles, images, and network connections a page is allowed to use. By blocking unapproved sources, CSP reduces the impact of cross-site scripting and data exfiltration.
Credential leakage is the unintended exposure of secrets such as API keys, tokens, and passwords. Common sources include JavaScript bundles, decompiled mobile apps, public Git repositories, browser network logs, and low-code platform configurations visible to users.
A Client Token is a scoped, revocable authentication credential designed for frontend web and mobile applications. It grants permission to invoke specific edge API pipelines while enforcing allowed-origin domains and rate limits, safely abstracting sensitive upstream API secrets.
A Web Application Firewall (WAF) is a security layer that inspects HTTP requests and blocks malicious traffic such as SQL injection, cross-site scripting, and known exploit patterns. It sits in front of web applications and APIs, filtering attacks before they reach origin servers.
Ready-to-Use Edge Recipes
To use OpenAI in a client-side React app without leaking your secret key, never include OPENAI_API_KEY or REACT_APP_OPENAI_API_KEY in frontend .env files. Instead, route your fetch calls through a RealComposer edge endpoint that injects your secret key server-side on Cloudflare Workers and enforces CORS origin whitelisting.
Webflow is a purely static and frontend visual builder with no backend server. To call private APIs from Webflow custom code without revealing secrets in the browser inspector, route requests through RealComposer. RealComposer stores your API keys in an AES-256-GCM vault, injects credentials at the edge, and handles CORS headers automatically.
You should not store Mailchimp credentials in JavaScript / HTML client code. Block browser extraction of list API keys via edge-only authorization headers. RealComposer Secret Vault injects headers on Cloudflare Workers so only your edge URL is public.