A01: Broken Access Control in Next.js
Next.js API routes and server actions are particularly susceptible to broken access control if developers assume that client-side routing provides security. Server-side checks must be implemented on every API route, server action, and middleware. Use Next.js middleware for route protection, but always verify permissions at the data access layer. Never rely on client-side checks alone.
Common pitfalls: Exposing admin API routes without authentication checks, trusting user IDs from request parameters without verification, and forgetting to protect Server Actions with session validation.
A03: Injection Flaws in Server Components
While React Server Components (RSC) reduce client-side attack surface, they don't eliminate injection risks. Server Components that directly query databases, read files, or execute shell commands are vulnerable to SQL injection, NoSQL injection, and command injection if input is not properly sanitised.
Mitigation: Use parameterised queries for all database operations, validate and sanitise all user inputs on the server, and avoid constructing shell commands from user-supplied data. Next.js's built-in CSRF protection for Server Actions should always be enabled.
A05: Security Misconfiguration
Common Next.js misconfigurations include exposing environment variables to the client (NEXT_PUBLIC_* misuse), leaving debug endpoints enabled in production, misconfigured CORS policies, and missing security headers. The Next.js security headers guide recommends strict CSP, HSTS, X-Frame-Options, and X-Content-Type-Options.
Tools: Use `next lint` with security plugins, implement Content Security Policy headers via next.config.mjs, and audit your bundle for exposed secrets.
A02: Cryptographic Failures in Next.js
Cryptographic failures — formerly called 'Sensitive Data Exposure' — occur when applications fail to adequately protect sensitive data such as passwords, payment card numbers, health records, or session tokens. In Next.js applications, common cryptographic failures include: storing passwords with weak or unsalted hashing algorithms (MD5, SHA-1), transmitting sensitive data over HTTP instead of HTTPS, exposing secrets in client-side JavaScript bundles via NEXT_PUBLIC_ prefix misuse, storing sensitive data in localStorage or sessionStorage without encryption, and using weak random number generators for token generation.
Mitigation: Use bcrypt or Argon2 for password hashing (never MD5 or SHA-1), enforce HTTPS at both the application and infrastructure level, keep sensitive data server-side only, and use cryptographically secure random generators (crypto.randomBytes in Node.js) for all tokens and session identifiers.
A04: Insecure Design in Next.js Applications
Insecure design is a broad category covering architectural flaws and missing security controls that cannot be fixed by good implementation alone — the fundamental design must change. In Next.js applications, insecure design manifests as: building API routes without rate limiting or abuse controls, designing authentication flows without account lockout after repeated failures, allowing unbounded file uploads without size and type validation, designing multi-tenant applications that share data without proper isolation, and failing to model the threats specific to your application's domain before writing code.
Mitigation: Conduct threat modelling before writing code — identify the most likely attackers, their goals, and the data they would target. Implement rate limiting on all authentication endpoints (Next.js middleware is an appropriate layer). Design file upload flows with strict MIME type validation, size limits, and malware scanning. Use security stories in your user story backlog: 'As an attacker, I want to enumerate user accounts by abusing the password reset endpoint.'
A06: Vulnerable and Outdated Components in the Next.js Ecosystem
The Node.js and React ecosystems are characterised by deep dependency trees. A typical Next.js application has hundreds of transitive dependencies — each a potential attack surface. Vulnerable and outdated components are exploited through known CVEs (Common Vulnerabilities and Exposures) in npm packages, outdated versions of Next.js itself, unpatched versions of React, and vulnerable authentication libraries.
Mitigation: Run npm audit in every CI/CD pipeline run and fail builds on High or Critical findings. Use Dependabot or Renovate for automated dependency updates. Subscribe to Next.js security advisories at nextjs.org/security and apply patches within 72 hours of a critical disclosure. Audit your package.json for packages with no recent maintenance activity — abandoned packages with known CVEs are a common breach vector. Never use packages from untrusted or unverified publishers.
A07: Identification and Authentication Failures in Next.js
Authentication failures in Next.js applications commonly include: implementing custom authentication instead of using a well-tested library (NextAuth.js, Clerk, Auth0), not invalidating session tokens on logout, generating predictable session IDs, not enforcing multi-factor authentication for administrative routes, allowing credential stuffing attacks through absent rate limiting, and storing session state client-side in unprotected cookies.
Mitigation: Use NextAuth.js or a managed authentication provider rather than hand-rolling auth. Set HttpOnly and Secure flags on all session cookies. Implement rate limiting on login endpoints — Next.js middleware with an in-memory or Redis-backed counter is an effective approach. Require MFA for all administrative users. Verify that logout actually invalidates the server-side session, not just removes the client cookie.
A08: Software and Data Integrity Failures
This category covers cases where code and data are not protected against integrity violations. In Next.js applications, risks include: loading third-party scripts without Subresource Integrity (SRI) hashes, deserialising untrusted JSON without schema validation, accepting webhook payloads without verifying HMAC signatures, using insecure CI/CD pipelines where build artifacts can be tampered with, and auto-updating npm packages without lockfile pinning.
Mitigation: Add SRI hashes to all externally hosted scripts (though the recommended approach is to self-host critical scripts entirely). Validate all incoming webhook payloads against an expected schema and verify HMAC signatures before processing. Pin dependency versions in package-lock.json and commit it to version control. Audit your CI/CD pipeline for untrusted build steps — a compromised GitHub Action in your pipeline can backdoor your production application.
A09: Security Logging and Monitoring Failures in Next.js
Most Next.js applications log too little to detect or investigate a breach. Security logging failures include: not logging authentication events (successful logins, failed attempts, password resets), not logging access to sensitive API routes, logging sensitive data such as passwords or tokens in plaintext, storing logs locally where they can be deleted or tampered with by an attacker who gains server access, and never reviewing logs for anomalous patterns.
Mitigation: Implement structured logging (JSON format) for all authentication events, access control decisions, and API responses. Include user ID, IP address, User-Agent, and timestamp in every security-relevant log entry — but never include passwords, tokens, or card numbers. Ship logs to a centralised SIEM (Splunk, Elastic, Datadog) where they are tamper-resistant. Set up alerts for: more than 5 failed login attempts from a single IP in 60 seconds, access to admin routes from unknown IPs, and any database error containing SQL keywords (potential injection probes).
A10: Server-Side Request Forgery (SSRF) in Next.js
SSRF vulnerabilities allow attackers to make the server fetch arbitrary URLs, potentially accessing internal services, cloud metadata endpoints, or other restricted resources. In Next.js, SSRF is most commonly introduced in: server-side API routes that accept a URL parameter and fetch it (e.g. image proxy routes, webhook validators, or link preview features), next/image's remotePatterns configuration if too permissive, and API routes that forward requests to backend services without validating the target URL.
Mitigation: Never allow user-supplied URLs to be fetched server-side without strict allowlist validation. Use next/image's remotePatterns with the minimum required hostnames — avoid wildcards. If you must fetch user-supplied URLs, validate against a strict allowlist of permitted domains and reject requests to private IP ranges (10.x.x.x, 172.16.x.x, 192.168.x.x) and cloud metadata endpoints (169.254.169.254 for AWS, 169.254.170.2 for Azure). In cloud deployments, use instance metadata service IMDSv2 with session token requirements to limit SSRF impact.
Security-First Next.js Development with Cyronix
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