Critical Bug: Task Agents Ignore Plan Mode Write Protect

This document details a critical bug where agents invoked via the Task tool circumvent Plan Mode write restrictions. Let's dive into the specifics of this security flaw and what it means for users.

Summary

Agents initiated through the Task tool possess the ability to write files even when the main assistant operates in Plan Mode (shift+tab). This action directly violates the core safety principle that Plan Mode is designed to prevent all write operations, ensuring a safe and controlled environment for users to review changes before execution.

Severity

CRITICAL - This issue poses a significant security and safety risk. It undermines the fundamental purpose of Plan Mode, potentially leading to unintended file system modifications and data breaches. Addressing this bug is paramount to maintaining user trust and data integrity.

Environment

• Claude Code Version: 1.0.71
• Model: claude-opus-4-1-20250805
• Platform: macOS Darwin 24.6.0
• Date: 2025-08-08

Steps to Reproduce

To replicate this bug, follow these steps:

1. Initiate Claude Code within a designated directory.
2. Engage Plan Mode by pressing shift+tab.
3. While in Plan Mode, trigger any agent through the Task tool that is equipped with write capabilities, such as the documentation-specialist.
4. Observe that the agent successfully writes files, despite Plan Mode being active. This demonstrates the bypass of the intended write restrictions.

Expected Behavior

When Plan Mode is active, the following behaviors should be observed:

• ALL write operations must be blocked to prevent unintended modifications.
• This restriction should extend to agents invoked through the Task tool, ensuring consistent enforcement of Plan Mode.
• Any attempt to write files should result in a clear and informative error message, alerting the user to the blocked operation.

Actual Behavior

• Plan Mode effectively prevents direct Write/Edit tool usage by the main assistant, demonstrating partial functionality.
• However, agents invoked via the Task tool retain the ability to write files, bypassing the intended restrictions.
• No error or warning is provided to indicate this bypass, potentially misleading users about the safety of Plan Mode.

Evidence

Session ID: 12f8749b-798c-4bce-b328-ca957eee43cb Timestamp: 2025-08-08T17:19:40 - 17:20:54

Sequence of events:

1. 17:14:28 - Plan mode initiated (active until 17:31).

2. 17:19:40 - documentation-specialist agent invoked via Task tool:

   {
     "name": "Task",
     "input": {
       "subagent_type": "documentation-specialist",
       "prompt": "Create a detailed implementation roadmap document..."
     }
   }
   

3. 17:20:54 - Agent successfully created file:

   File created successfully at: /Users/user/Desktop/2025-08-08-find-git/IMPLEMENTATION_ROADMAP.md
   

4. 17:31:16 - Plan Mode exited using ExitPlanMode tool.

Impact

The implications of this bug are significant:

• Security Risk: Plan Mode is designed as a crucial safety mechanism to prevent accidental or malicious file system modifications. Bypassing this protection exposes users to potential data breaches and system instability.
• User Trust: Users depend on Plan Mode to carefully review changes before they are executed. This bug undermines that trust and could lead to users questioning the reliability of the system.
• Data Safety: Unauthorized writes could modify or overwrite critical files, resulting in data loss, corruption, or compromise.

Root Cause Analysis

The Task tool appears to launch agents in a separate context that does not inherit the Plan Mode restrictions from the parent session. These child agents operate with their own set of tool permissions, which are not constrained by the parent's Plan Mode state. This discrepancy allows them to bypass the intended write restrictions.

Suggested Fix

To address this critical bug, the following solutions are recommended:

1. Immediate: The Task tool should be modified to verify the parent session's Plan Mode state before allowing child agents to perform any write operations. This check should act as a gatekeeper, preventing unauthorized writes.
2. Comprehensive: Implement a system-wide mechanism to ensure that all tool invocations, including nested or child agent calls, respect the Plan Mode state of the root session. This will create a consistent and reliable enforcement of Plan Mode restrictions.
3. Safety Check: Introduce an explicit Plan Mode state propagation mechanism to all agent invocations. This will ensure that the Plan Mode state is consistently passed down to all child agents, preventing any potential bypass.

Workaround

Until a permanent fix is implemented, users should adopt the following workarounds:

• Refrain from using the Task tool while in Plan Mode to avoid potential unintended writes.
• Recognize that Plan Mode does not currently prevent writes from agents invoked through the Task tool.
• Thoroughly verify that no unintended files were created after using agents in Plan Mode to mitigate any potential data breaches.

Additional Context

An IMPLEMENTATION_ROADMAP.md file (13,491 bytes) was unexpectedly created at 10:20 AM while the assistant was in Plan Mode. This file creation was not initiated by the user and directly violated the Plan Mode contract, highlighting the severity of the bug.

Reproducibility

100% - This behavior is consistently reproducible, indicating a systemic issue rather than an isolated incident.

Priority

This issue should be classified as a P0/P1 bug due to its compromise of the fundamental safety guarantee provided by Plan Mode. Immediate action is required to address this critical vulnerability and restore user trust.

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Bug report generated after discovering unexpected file creation in Plan Mode session

This bug report highlights a critical flaw in Claude Code's Plan Mode, where agents invoked via the Task tool can bypass write restrictions. This poses a significant security risk and undermines user trust. Addressing this issue requires immediate attention and a comprehensive solution to ensure the safety and reliability of Plan Mode. By implementing the suggested fixes and workarounds, we can mitigate the risks and restore confidence in the system.

By understanding the implications of this bug and taking proactive measures, users can protect their data and maintain a safe and secure development environment. It's essential to stay informed about such vulnerabilities and adopt best practices to minimize potential risks.

For more information on secure coding practices and vulnerability management, you can visit the OWASP Foundation website. OWASP is a trusted resource for developers and security professionals, offering valuable insights and guidance on building secure applications.