JavaScript Security
Interview Questions

Cross-Site Scripting (XSS) is a vulnerability where an attacker injects malicious scripts into content from otherwise trusted websites. There are three types: stored, reflected, and DOM-based. Prevent XSS by validating and escaping user inputs, setting Content Security Policy (CSP) headers, and using secure libraries to sanitize inputs.

CSRF is an attack that forces a user to execute unwanted actions on a web application where they're authenticated. To prevent CSRF, employ anti-CSRF tokens that ensure requests come from legitimate users. Each session generates unique tokens that must be verified before processing requests.

Common JavaScript security risks include XSS, CSRF, Clickjacking, and data exposure. Mitigation involves enforcing CSP to control resource loading, using Subresource Integrity (SRI) to ensure integrity of external scripts, and adopting secure coding practices such as proper input validation and escaping output.

In a previous project, we identified an XSS vulnerability during a security audit. I led the effort to implement input validation and output escaping. We also trained the team on secure coding practices, resulting in enhanced security with no further incidents.

First, assess the vulnerability’s potential impact on the application. Check for any updates or patches provided by the library maintainers. If none are available, communicate the risk to the team and consider switching to a secure alternative library or implementing a temporary patch until an official fix is issued.

Content Security Policy (CSP) is a security feature that helps prevent various attacks like XSS by specifying HTTP headers that restrict how web pages load or execute content. CSP controls which resources can be loaded, thus blocking certain types of attacks by restricting script execution to trusted sources.

Review the code for unsanitized user inputs, unescaped outputs that could lead to XSS, misuse of functions like eval, and reliance on outdated third-party libraries. Propose code changes or best practices that mitigate these risks.

In a large codebase, implement secure coding standards and guidelines. Conduct regular security audits and use static code analysis tools to detect vulnerabilities early. Ensure all libraries are up to date and incorporate security patches promptly. Educate the team on security best practices and response procedures to foster a robust security culture.

To secure AJAX communications, always use HTTPS to encrypt data in transit. Implement CSRF protection measures like anti-CSRF tokens. Validate all input and sanitize output to prevent XSS vulnerabilities. Also, apply tokens or JWTs for secure authentication of requests.

Validating user input is crucial in preventing injection attacks like SQL injection and XSS, ensuring the integrity of data processed by applications. Achieve this by utilizing input sanitization libraries, employing strict type checks, and ensuring validation on both client and server sides for robustness.

Mitigate risks by employing Subresource Integrity (SRI) to verify the integrity of external scripts. Enforce a strict CSP to control the execution of third-party scripts. Regularly review and audit the code of libraries and limit permissions and capabilities of third-party scripts to essential actions only.