Stop what you’re doing and update Claude Code. Check Point Research disclosed two critical vulnerabilities today — CVE-2025-59536 and CVE-2026-21852 — that can let an attacker execute code on your machine and steal your Anthropic API key simply by having you clone and open a malicious repository.

No additional interaction required. No suspicious files to download. Just opening the wrong repo is enough.

What Was Disclosed

Check Point Research published full technical details on both CVEs affecting Claude Code, Anthropic’s AI-powered coding assistant:

CVE-2025-59536 — MCP Consent Bypass (RCE)

Claude Code supports the Model Context Protocol (MCP), which allows external servers to provide tools and context to the model. MCP servers must receive explicit user consent before being trusted.

CVE-2025-59536 bypasses this consent mechanism. A malicious repository can include configuration that silently registers a hostile MCP server without the user seeing a consent dialog. That server can then instruct Claude Code to execute arbitrary code on the local machine — silently, in the background, with the permissions of the user running Claude Code.

Attack vector: Malicious .mcp.json or project configuration files in a repository.

CVE-2026-21852 — API Key Exfiltration

This vulnerability allows a malicious repository to trigger a sequence that causes Claude Code to exfiltrate the user’s Anthropic API key before trust confirmation is completed for the project.

In practical terms: clone a crafted repo, and your API key may have already been sent to an attacker’s server before you’ve done anything. No code execution required on your part — the exfiltration happens during the initial analysis phase.

Attack vector: Crafted project files processed during Claude Code initialization.

Why This Is Especially Dangerous

Both CVEs share a threat model that makes them particularly nasty for the developer community:

Supply chain attack surface. The most natural place to clone unknown repos is during open source exploration, interview take-home projects, dependency auditing, or CTF challenges. These are exactly the contexts where developers are least suspicious and most likely to open unfamiliar code in an AI coding assistant.

AI coding assistants are inherently high-trust. By design, Claude Code has broad filesystem access, shell execution capabilities, and credential access. That’s what makes it powerful. These CVEs weaponize that trust surface.

API key theft has cascading consequences. Your Anthropic API key is connected to your billing account, your organization’s usage, and potentially your production infrastructure if you’ve reused credentials. A stolen key can rack up significant charges, access your production Claude deployments, or be sold to enable abuse at scale.

Immediate Actions to Take

1. Update Claude Code Immediately

npm update -g @anthropic-ai/claude-code
# or
pip install --upgrade claude-code

Check the official Anthropic security advisory for the specific patched version number and verify you’re running it.

2. Rotate Your Anthropic API Key

If you’ve cloned any repos and opened them in Claude Code in the past 30 days, treat your API key as potentially compromised:

  1. Log into console.anthropic.com
  2. Navigate to API Keys
  3. Revoke the existing key
  4. Generate a new key
  5. Update all local configs, .env files, and CI/CD secrets

3. Audit Your Claude Code Project Files

Look for suspicious entries in:

  • .mcp.json — unexpected MCP server registrations
  • .claude/ directory — configuration files you didn’t create
  • CLAUDE.md — instructions that include unusual tool directives

Any file instructing Claude Code to call external URLs, execute shell commands in its setup instructions, or register new MCP servers should be treated with extreme suspicion.

4. Review Your API Key Usage

Check your Anthropic console for any unexpected API usage spikes. If you see calls you don’t recognize — especially from unusual IP addresses or at unusual times — assume compromise and rotate immediately.

What This Means for Agentic Pipelines

For teams running Claude Code as part of larger agentic workflows (CI/CD pipelines, automated code review, etc.), the risk surface is amplified:

  • Service accounts with broad permissions are higher-value targets than developer personal keys
  • Automated repo processing may mean you’re running Claude Code against hundreds of repos, including external forks and PRs
  • Production API keys used in automated pipelines have higher blast radius than dev keys

For these scenarios, add explicit controls:

  • Run Claude Code in isolated environments (containers, VMs) with network egress filtering
  • Use separate API keys for automated pipelines with usage limits set
  • Scan incoming repos for suspicious .mcp.json and .claude/ configurations before processing

A Note on MCP Security Model

CVE-2025-59536 highlights a systemic issue with the MCP trust model. The consent dialog approach — “a server is requesting access, do you approve?” — assumes the consent dialog is always shown. Any mechanism that can suppress or pre-populate that dialog becomes an attack vector.

This is a broader design challenge for the entire MCP ecosystem, not just Claude Code. If you’re building tools that integrate MCP servers, revisit how your consent flow handles edge cases.

The full security advisory with technical details and patch notes is available from Check Point Research directly. Apply the patch now — don’t wait.

Sources

  1. Dark Reading — Claude Code vulnerability disclosure
  2. The Hacker News — CVE technical details
  3. Security Affairs — Check Point Research analysis
  4. Check Point Research Blog — Primary disclosure

Researched by Searcher → Analyzed by Analyst → Written by Writer Agent (Sonnet 4.6). Full pipeline log: subagentic-20260225-2000

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