🔐 The hole behind the convenience: Claude MCP + Cursor security risksUnderstanding and using it

A single security setting could compromise your entire MVP

These days, you can whip up an MVP in no time just by integrating a couple of AI tools like Claude or Cursor. GPT polishes your language, Claude gives emotionally resonant answers to questions, and Cursor IDE turns your thoughts into code.

Even a 20-year veteran developer says, "Wow, the world has really improved." Seeing me, a non-developer, whip up an MVP server, it must feel unfair from the perspective of someone who developed in C. Yet, we often don't know where the conversations or code exchanged with AI are stored or where they're transmitted.

Claude stores logs for 30 days by default, and Cursor can send your entire repository information externally with its default settings. Yet most people feel reassured by this convenience and remain indifferent to security settings.

But most security incidents aren't caused by hacking—they're "problems arising from not setting things up."

1. Observe: Actual leaks stem more from 'configuration errors' than technical flaws

Claude and Cursor are extremely useful for AI-powered workflow automation, but using them with default settings carries a constant risk of information leakage.

✅ Core Issue

• The Claude API stores prompt and response data for 30 days by default
• Cursor IDE sends work logs and code snippets to external servers when Privacy Mode is OFF
• Users often input sensitive data without realizing this

📌 Leak Scenarios Scenario 1

If a request containing the API Key is sent to Claude → It is stored verbatim in the logs

✅ Situation

Situation where a user directly asks Claude about API usage:

이 API 키로 사용자 리스트 가져오려면 어떻게 해야 해?  
API Key: sk-test-51a23abc456defg789

⚙ How it works

• The Claude API (MCP) stores prompts and response logs for 30 days by default.
• Without a separate contract (Enterprise plan) or configuration, these are stored on the server.
• Within the Claude system, Anthropic's internal operations team has access to these logs (unless on an Enterprise plan).

🧨 Path of Occurrence

1. API Key included in the prompt → Transmitted to Claude
2. Claude API servers automatically log this content
3. Logs are retained for 30 days and can be accessed for internal auditing or debugging
4. May be exposed during internal audits or error debugging without external compromise

📊 Risk Assessment

Item	Risk Level
Scope of Exposure	1 API Key → Potential access to entire server
Potential for internal exposure	Accessible to Anthropic internal operations team
External Exposure Potential	Low (No direct hacking, but weak security)
Risk of human error	High (Developers, planners, and marketers all habitually ask GPT)

📌 Leak Scenario 2

Cursor with Privacy Mode OFF → Entire code automatically uploaded

✅ Situation

• Writing Claude integration prompts
• .env, config.json, api_keys.py Indexing repositories containing Claude integration prompts

⚙ How It Works

• When Privacy Mode is OFF, work history is sent to external servers like Cursor logs + Fireworks
• When indexing repositories, the entire structure is uploaded externally in chunks
• Without filtering .env, potentially including sensitive files

🧨 Occurrence Path

1. Indexing a repository containing sensitive files
2. Cursor automatically analyzes and saves
3. Some code structure and configuration values are transmitted to third-party servers
4. Stored for up to 30 days or more depending on external server log retention period

📊 Risk Assessment

Item	Risk Level
Scope of Leakage	Entire project structure + sensitive configuration values
Potential Internal Exposure	Accessible by Cursor team or connected external platforms
External Exposure Risk	Possible during man-in-the-middle attacks or API integration issues
Likelihood of Error	Very high (Initial state is ON by default with insufficient notifications)

2. Connecting: The Triple Risk Created by Claude + Cursor + User Habits

Actual information leaks do not stem from a single tool issue, but occur when the Claude API + Cursor IDE + user behavior intersect.

Simultaneous exposure of these three components creates unexpected security vulnerabilities.

Component	Key Risk
Claude MCP	– Default 30-day log retention – Dangerous commands possible upon tool registration – Transmission records not removed if settings are inadequate
Cursor IDE	– Logs stored and externally transmitted when Privacy Mode is OFF – Risk of including sensitive files when indexing entire repositories
User Habits	– Sharing prompt screens during meetings- API key exposure via captured images- Sharing sensitive code snippets on Slack/Notion

🎯 Key Insight

Tool security → IDE settings → Human habits: When all three become lax simultaneously, actual security incidents quietly occur.

3. Discovering the Principle: The Most Common Mistakes

Actual leaks mostly stem from "habits"

Bad Habits	Potential Risks
Directly entering API keys into Claude	Server Access Privilege Leak
Cursor Privacy Mode OFF	Transmission of Entire Project Logs
Uploading to GitHub .env Upload	Service fully exposed
Enter actual URL/path in prompt	Service structure leakage to competitors

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4. Practicing Security Safety: Claude MCP + Cursor Security Checklist

Claude API

• Request Zero-Retention setting on Enterprise plan
• Do not call the API directly from the frontend; only call it from the backend
• Do not directly input API keys, URLs, or product names in prompts → <<KEY>>, <<URL>> Use

MCP Tool

• Mandatory JSON schema implementation during registration
• Execute results in Sandbox first
• Set tool permissions with separate read/write access

Cursor IDE

• Privacy Mode must be enabled
• Indexing is only permitted up to the README level
• .cursorignoreIncludes the following:

.env  
credentials.json  
secret.py

Organization security policy

• Core documents encrypted and stored using Git-crypt or Age
• External collaborators must sign NDAs + minimize access permissions
• Quarterly Red Team security assessments conducted