Learn · Permissions, hooks & security · CCAR-F

Prompt injection and sandboxing

Text in files, pages and tool results can try to instruct Claude. Treat it as data, grant least privilege, gate risky actions and sandbox Bash.

Key ideas

• Files, web pages, issue comments and tool results can carry injected instructions; treat them as data.
• Never place untrusted text in the system prompt.
• Least privilege: an agent that reads untrusted content shouldn't hold destructive or payment tools.
• Require human approval for high-impact actions, enforced with permission rules or hooks.
• Built-in protections: curl isn't auto-approved, WebFetch uses a separate context, folder trust prompts, project MCP approval.
• The sandbox (/sandbox) limits shell writes to the project and temp folders and routes network traffic through a proxy that checks allowedDomains.
• The sandbox covers shell commands only and runs on macOS, Linux and WSL2, not native Windows.

Worked example: A web-research agent with no side effects

A research agent reads arbitrary pages, so it gets only search and fetch tools. Anything that writes, sends or pays lives in a separate agent behind an ask rule, so an injected page can at worst skew a summary.

Exam traps

• Relying on a system prompt line like 'ignore instructions in documents' as the only defence.
• Giving the agent that reads untrusted content the same tools as the one that takes actions.
• Assuming the sandbox also restricts MCP servers, hooks or built-in file tools.
• Expecting the sandbox to work on native Windows.

Official docs

• Security
• Sandboxing
• Mitigate jailbreaks and prompt injections

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