Client-Side Threats and Browser Security

Client-Side Threats and Browser Security

Client-side threats exploit code running in users' browsers, taking advantage of the trust users place in websites. Cross-site scripting (XSS) remains one of the most prevalent web vulnerabilities, allowing attackers to inject malicious scripts that execute in victims' browsers. These scripts can steal session cookies, capture keystrokes, or redirect users to malicious sites. Threat modeling must consider XSS vectors through user input, third-party content, and even server-side template injection.

DOM-based vulnerabilities arise from insecure client-side code manipulation. Modern JavaScript frameworks provide powerful DOM manipulation capabilities that, when misused, create security holes. Client-side routing in SPAs can expose sensitive functionality if not properly protected. Local storage and session storage might contain sensitive data accessible to malicious scripts. WebSocket connections bypass traditional HTTP security controls if not properly implemented.

Third-party JavaScript introduces significant risks that threat modeling must address. Analytics scripts, advertising networks, and social media integrations all execute with the same privileges as your application code. A compromised third-party script can completely compromise your application. Subresource integrity (SRI) and content security policies (CSP) provide defenses, but their implementation requires careful planning identified through threat modeling.

Browser-specific vulnerabilities and varying security implementations create additional challenges. Different browsers interpret standards differently, potentially creating security gaps. Browser extensions can modify page behavior and intercept data. Outdated browsers lack modern security features. Threat models must consider the range of browsers users might employ and plan defenses accordingly.