Identify security vulnerabilities with Claude

Modern software systems face constant pressure from evolving threats, but identifying real security vulnerabilities quickly and with confidence is still one of the hardest parts of the job.

Between noisy alerts, unfamiliar code, and high-stakes consequences, even experienced engineers can lose time to false positives or hard-to-spot flaws.

Claude helps teams surface, verify, and resolve security issues without adding overhead through two powerful tools:

• Claude.ai: Anthropic’s AI coding tool, available in your browser, that helps you inspect system behavior, audit unfamiliar code, and reason through potential vulnerabilities — all through natural language.
  
• Claude Code: Anthropic’s agentic coding tool that integrates directly with your development environment and helps you detect, debug, and address security flaws at the source.

This article walks through how engineers use both versions of Claude to detect vulnerabilities, debug safely, and ship secure code with more confidence.

Explore threat models and spot risks with Claude.ai 

Claude.ai helps you reason through security concerns before diving into code. It's especially useful when you want to:

• Explore threat models for a new feature
• Review insecure patterns or anti-patterns in a repo
• Break down a CVE and see if your project's exposed
• Generate hardening checklists or audit plans

You can paste code snippets, describe the system, or even link to documentation. Claude.ai helps surface the kinds of risks that don't show up in a static scan. For example:

What are the security concerns with storing tokens in localStorage in a React app?

Claude.ai might flag exposure to XSS attacks and suggest alternatives like HttpOnly cookies with CSRF protection. You can also prompt it to list relevant mitigation options, helping you plan defenses proactively.

Security issues often hide in edge cases, places where logic doesn't behave as expected under unusual inputs or timing. Claude.ai can help you reason through those cases more effectively when you include actual code. Rather than just describing the function, paste it directly into your prompt:

Here's our OAuth callback handler. Walk through edge cases that might introduce security risks.

app.get('/auth/callback', (req, res) => {
  const { state, code } = req.query; 
  if (!state || !code) return res.status(400).send('Missing params');
  if (!verifyState(state)) return res.status(403).send('Invalid state');
  exchangeCodeForToken(code).then(token => {
    setSessionToken(req, token);
    res.redirect('/dashboard');
  });
});

With this context, Claude.ai can flag concerns like:

• Race conditions during exchangeCodeForToken if not properly scoped or locked
• Lack of input validation on code and state, exposing potential SSRF or callback injection vectors
• Session fixation or replay attacks if setSessionToken doesn't regenerate session IDs
• Redirect abuse, e.g., open redirect attacks if the destination isn't controlled

You can then ask Claude.ai follow-up questions:

Could this handler be vulnerable to CSRF or replay attacks? If so, how should we mitigate them?

Claude.ai provides layered responses—explaining the risk, suggesting validation strategies, and optionally refactoring the handler to use anti-CSRF tokens or restrict redirect targets. By exploring these scenarios in natural language, you can uncover gaps and plan fixes before they become production issues.

Think through architecture-scale security decisions with Claude.ai 

Sometimes you're not scanning for bugs; you're making long-term security decisions. Claude.ai helps you reason through bigger questions with extended thinking. For example:

What's the best way to implement rate limiting in a multi-tenant SaaS app?
Think through how to protect a message queue from replay attacks.
How should we handle file uploads to prevent RCE or DoS risks?

Claude.ai breaks these down step by step, explaining tradeoffs and recommending implementation patterns.

Triage and fix security issues with Claude Code 

When you're ready to act on security findings, Claude Code is the tool of choice. This terminal-based, agentic coding tool reads from your local project and interacts directly with your codebase. You can use it to find vulnerabilities, understand how they propagate, and apply scoped, permissioned fixes.

Once installed via:

npm install -g @anthropic-ai/claude-code

You can run diagnostic queries like:

scan the auth module for insecure token handling

Claude Code inspects your logic, flags weak patterns like predictable tokens or inadequate expiration rules, and explains its reasoning based on context.

To trace behavior across files:

find where user roles are assigned in the onboarding flow

Claude Code maps out the execution path and highlights whether that logic can be bypassed, misused, or influenced by external input. This saves valuable time compared to manually tracing flows or relying on static analysis alone.

When you're ready to fix an issue:

harden this endpoint against SSRF attacks

Claude Code proposes safe changes, adds checks or sanitization, and asks for confirmation before making edits. This workflow keeps you in control while leveraging Claude's security expertise to implement best practices.

Build security regression tests with Claude Code 

A fix is only useful if it holds. Claude Code helps you build guardrails that validate security behavior across changes. For example:

write a regression test to confirm tokens expire correctly

Claude Code adds tests using your preferred framework, like Jest, Mocha, or Pytest, mirroring your conventions and targeting critical edge cases. You can also prompt it to increase coverage in sensitive paths:

add tests for all auth-related middleware

This helps tighten security over time without introducing flakiness or manual overhead. Engineers report up to 30% improvement in security test coverage when using Claude Code to augment their test suites.

Catch vulnerabilities in CI with Claude Code 

Security checks are even more valuable when they happen before code hits production. Claude Code can run in CI to scan for risks and block merges with actionable results without requiring manual reviews.

Claude Code supports headless execution using the --print flag. You can run security queries as part of your pipeline:

scan this diff for common security risks like SQL injection or open redirect

Claude Code reads the repo, evaluates context, and returns structured output. From there, you can gate merges on high-severity findings, extract summaries for PR comments, or flag issues that need review.

To enforce security baselines across every push:

check for hard-coded credentials, unsafe evals, and missing auth checks

This approach gives you real security coverage, not just linting or SAST signatures, but reasoning-based analysis scoped to your codebase. Claude Code adapts to your stack, your conventions, and your risk model.

You can also embed quality controls:

write unit tests for recently changed functions that touch the payments module

The result is tighter guardrails and less risk slipping through under time pressure. Teams using Claude Code in CI/CD pipelines have reported fewer critical bugs at release time and cleaner audit trails during reviews. Since Claude Code operates directly from the terminal, it integrates into existing workflows without extra dashboards or plugins.

Choosing the right Claude tool for security

Each of these two tools fits naturally into a different stage of the process.

Claude.ai reviews insecure patterns in code and guides architecture-scale security decisions. It’s free and available on web, desktop, and mobile.

Claude Code reviews insecure patterns, triages and fixes vulnerabilities in your local codebase, and builds security regression tests that catch issues in CI/CD pipelines. You can use it from the terminal if you have API access or a Max plan subscription.

In general, use Claude.ai for high-level security planning, threat modeling, and architectural decision-making. It's the fastest way to explore risks and devise defenses without diving into code.

Switch to Claude Code when you need to find, fix, and prevent vulnerabilities directly in your codebase. Its deep integration with your local development environment and CI/CD pipelines makes it a powerful tool for hands-on security work.

Get started 

Ready to build more secure systems with Claude? Here's how to begin:

1. Visit Claude.ai and sign up for free. Use it to explore threat models, reason through attack scenarios, and plan security improvements.
   
2. When you're ready to put those plans into action, install Claude Code and run it in your terminal:

npm install -g @anthropic-ai/claude-code
cd your-project
claude

With Claude, you can finally make security an integral part of your development process. The result? Code reaches production faster, with stronger security and fewer hidden vulnerabilities.