Monday, February 17, 2025

Single Page Application Common Vulnerabilities And Fixes

Your Single Page Application Are Risky: How to Fix Them

Introduction

Single-page applications (SPAs) are popular for their dynamic and user-friendly interfaces, however they pose security vulnerabilities. SPAs’ client-side rendering makes them vulnerable to data tampering and unauthorised access. This blog article will discuss SPA vulnerabilities such routing manipulation, hidden element exposure, and JavaScript debugging and offer solutions.

What is the single page application?

An application or website that interacts with the user by dynamically rewriting the current page instead of loading whole new pages from the server is called a Single Page Application (SPA). Because it eliminates the conventional full-page reloads, this method enables a smooth and quick user experience that is comparable to a desktop application.

Single Page Application architecture

SPA web applications return a single page with JavaScript-hidden, displayed, or updated content. It contrasts from the flat file application framework used in PHP or HTML sites and the Model-View-Controller (MVC) design, which separates data, views, and server controls. SPAs update dynamic data using API calls, eliminating page refreshes and URL changes. SPAs seem more like native apps with this technique, providing a smooth user experience. React, Angular, and Vue are popular JavaScript SPA frameworks.

Client-side rendering

Client-side rendering SPAs return an HTML document with only CSS, metadata, and JavaScript. The HTML document is empty until the JavaScript files are launched in the browser and the application’s frontend UI and content are loaded. JavaScript uses the URL to generate the requested page if the application uses routing. While doing this, the application requests data from the API endpoint and checks if the user is authorised. The application will display a login page or send a user to an SSO application if they are not authenticated.

Before the application dashboard or login page loads, a user may see a blank white page. The program may load hundreds of thousands of lines of minified JavaScript to build the user experience during this wait. Worldwide, millions of apps employ SPAs, including Netflix, Hulu, Uber, and DoorDash.

Client-Side Rendering Issues

Because SPAs render content using API data in the client’s browser, users have tremendous influence over the application. This allows free application manipulation, making user or role impersonation easy.

Routing

Routes are essential to Single Page Application JavaScript frameworks. These frameworks imply application pages with routes. Users can see dashboards and profiles as routes. The client’s browser handles all JavaScript, thus they may see these routes in the application source’s JavaScript files. Users can access these channels if they know them. Depending on how JavaScript was built, users may be checked for route access.

Hidden Elements

SPAs control access via hidden page elements. When the page loads, the program validates the user’s role using local/session information, cookie values, or server answers. After checking the user’s role, the app displays or conceals elements. The application may only render user-accessible elements. Some applications render all elements but “hides” them using CSS attributes. Browser Developer Tools expose hidden elements, allowing users to force display. Hidden elements may be form fields or connections to other pages.

JavaScript Debugging

Modern browsers offer real-time JavaScript breakpoint debugging. JavaScript files can have breakpoints placed to change variables or rewrite functions in modern browsers. Core function debugging can overcome access constraints and allow unauthorised page access.

The previously described function reads a user’s cookie, Base64 decodes it, separates it using :, and authenticates the user if the values match. Identifying these essential operations lets an attacker overcome client-side application authorisation and access controls.

Exploitation

Some methods make manual JavaScript framework issue exploitation easier, but it requires time and practice. JavaScript files are often analysed to find application paths. Finding routes lets you “force-browse” application pages without using the UI. This method may work alone, but you may need to find application role checks. Use the JavaScript debugger to alter variables during execution to evade authorisation or authentication checks. Another method is to use an HTTP proxy like Burp Suite Professional to capture server replies to user information queries and manually change the user object. These exploitation methods are successful, but strong preventative measures, like those in this piece, can mitigate them.

The previously described function reads a user’s cookie, Base64 decodes it, separates it using :, and authenticates the user if the values match. Identifying these essential operations lets an attacker overcome client-side application authorisation and access controls.

Recommendations

Systemic access control issues plague client-side JavaScript frameworks. After loading the application into their browser, there are limited techniques to prevent unauthorised content interaction. An attacker’s impact is greatly mitigated by robust server-side access control checks on APIs. The attacker may see what a page would look like as an administrator or the structure of a privileged request, but not restricted data.

Log and monitor API calls to detect unauthorised access to protected data. Periodic penetration assessments of web applications and APIs over their lifespan might identify security flaws. Penetration testing should reveal APIs with insufficient access control implementations, allowing for fixes before an adversary exploits them.

API Access Control

Single Page Application security requires strong API access controls. To prevent users from forging or changing session tokens, access control mechanisms should employ a JSON Web Token (JWT) or other unique, immutable session identifier. APIs should validate session tokens and enforce role-based access for every interaction. APIs typically check user authentication but not endpoint role access. Sometimes one incorrect endpoint compromises an application. If all application endpoints except the admin endpoint that generates new users check a user’s role, an attacker can create users of any role, including admin users.

 Proper API access control example
Proper API access control example

This diagram demonstrates a user authenticating, obtaining a JWT, and producing a page. The SPA receives a page request. Single Page Application knows the user isn’t authenticated, so JavaScript renders the login page. The SPA sends the login request to the server via API. The API authenticates the user and offers a JWT for future queries. After receiving the server answer, the SPA caches the JWT and renders the dashboard the user requested.

The Single Page Application also asks API data to render the page. API data is returned to the program and displayed to the user. Next, the user bypasses client-side access controls and requests the application’s main admin page. API queries by the SPA render admin page data. Since the user is not an admin user, the backend server produces a 403 error stating that the user cannot access the data.

Figure 1 illustrates how API access rules restrict data access. As seen, the user could view the page in the Single Page Application, but API access rules prevented them from accessing the data needed to render it. C# and Java frameworks provide annotations to simplify access control for APIs.

Server-side rendering

Svelte-Kit, Next.js, Nuxt.js, and Gatsby are JavaScript frameworks with server-side rendering that can alleviate this issue in addition to API access constraints. MVC and SPA architectures combine in server-side rendering. After rendering the Single Page Application page, the server delivers the user only the final output. Routing, rendering, and access controls are no longer handled by the client browser. Before producing HTML, the server can apply access control rules to restrict access to specific components or data.

 Server-side rendering example
Server-side rendering example

Users access server-side rendered applications in this diagram. The server verifies the user’s authentication and authorisation after requesting an authenticated page in the application. Since the user is not authenticated, the application displays the login page. After authentication, the server constructs the session, sets cookies or tokens, and redirects the user to the application dashboard. After being routed, the user requests data, the server validates authentication, and because the user has permissions to access the page, it produces the dashboard with the data.

User finds admin page URL and tries to access it. In this case, the app validates user role and authentication. The user cannot visit the page without the admin role, hence the server returns a 403 Forbidden or an error page.

A final Word

When rendered client-side, SPAs provide a dynamic and interesting user experience but present unique security problems. Developers can reduce risks by recognising SPA vulnerabilities including routing manipulation, hidden element exposing, and JavaScript debugging. Server-side rendering, API security, and access controls protect SPAs from unauthorised access and data breaches. Regular penetration testing and security assessments can improve Single Page Application security by discovering security flaws and allowing developers to fix them before they are abused. Developers can ensure SPAs provide a seamless user experience and secure sensitive data by prioritising security best practices.

Thota nithya
Thota nithya
Thota Nithya has been writing Cloud Computing articles for govindhtech from APR 2023. She was a science graduate. She was an enthusiast of cloud computing.
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