What is XSS?

Cross-site scripting (XSS) is a type of web vulnerability that allows attackers to inject malicious scripts into otherwise trusted web applications. These scripts can be used to steal session cookies, hijack user accounts, or perform unauthorized actions. XSS remains a relevant threat even in modern web frameworks like Angular, particularly when developers override or bypass built-in security features.

For enterprise applications that process sensitive user data, even one unmitigated XSS flaw can lead to significant data breaches or compliance violations. This makes proactive detection and prevention critical to maintaining application integrity.

Types of XSS in Angular apps

Stored XSS

Stored XSS occurs when a malicious script is permanently stored on the server (e.g., in a database) and later rendered in the browser. In Angular apps, this might occur if user input is saved and later displayed using innerHTML without proper sanitization.

Reflected XSS

Reflected XSS happens when user input is immediately echoed by the application in a response, such as in query parameters or form fields. If Angular templates render this data directly without escaping, attackers can exploit the reflection to run arbitrary scripts.

DOM-based XSS

DOM-based XSS arises from client-side JavaScript manipulation of the DOM using unsanitized user input. This can occur outside of Angular's template rendering, especially when developers manually update the DOM using document.write() or element.innerHTML.

Angular’s security model for XSS

Angular includes several robust security mechanisms that should eliminate many common XSS vulnerabilities by default. Understanding these features and using them correctly is the key to building and maintaining a secure Angular application.

Contextual escaping

Angular automatically escapes content depending on its context (e.g., HTML, URLs, attributes). This prevents malicious scripts from being executed in most scenarios unless security features are explicitly and deliberately bypassed.

Automated input sanitization

Angular sanitizes potentially dangerous content automatically when rendering data in templates. This includes filtering out script tags and other potentially dangerous markup before adding it to the DOM and displaying it to the user.

Bypassing Angular’s security checks

While the Angular security model is strong, developers can still inadvertently introduce risk by bypassing its protections. Special functions like DomSanitizer.bypassSecurityTrustHtml() allow developers to manually mark potentially unsafe content as trusted, which can reintroduce XSS risks if not used carefully.

In enterprise environments, these risks are magnified due to complex user flows, third-party integrations, and dynamic content rendering. Systematic testing using tools like Invicti DAST helps mitigate this by dynamically scanning running web applications, including Angular apps, and identifying exploitable vulnerabilities that were missed or did not yet exist during development.

Invicti’s DAST-first approach uncovers real-world XSS vulnerabilities with proof-based accuracy, eliminating false positives for exploitable issues and providing full visibility across the application’s attack surface. This allows teams to confidently identify and remediate security issues early and often.

Preventing cross-site scripting in Angular apps

To effectively prevent XSS in Angular apps:

• Avoid using innerHTML and similar unsafe DOM manipulation operations.
• Use Angular’s data binding syntax of {{ }} instead of manual rendering.
• Never bypass Angular’s built-in sanitization unless it’s justified and absolutely necessary.
• Validate and sanitize user input at all entry points.
• Integrate a dynamic vulnerability scanner like Invicti into your DevOps pipeline to test your applications for runtime XSS vulnerabilities in a continuous process.

Modern Angular applications can be resistant to many XSS attacks by default, but only if developers correctly use protections provided by the framework and validate them through runtime testing. What’s more, even a safe framework like Angular cannot protect against XSS introduced through unsafe libraries or third-party code injected into the DOM, making it vital to test the entire application as deployed. Building Invicti into your development workflows helps ensure your Angular apps stay secure as they move into production and grow.

Schedule a demo with Invicti to see how our DAST-first, proof-based application security platform solution can identify vulnerabilities and empower your team to fix them fast.