Critical Bug: Task Tool Bypasses Plan Mode Write Protection

by Alex Johnson 60 views

Introduction

In the realm of software development, maintaining the integrity and security of applications is paramount. A critical vulnerability has been identified in Claude Code, version 1.0.71, that undermines a core safety mechanism: Plan Mode. This bug allows agents invoked via the Task tool to bypass write restrictions enforced by Plan Mode, potentially leading to unintended file system modifications and data corruption. This article delves into the specifics of this bug, its implications, and the steps being taken to address it. Understanding the nature of this vulnerability is crucial for developers and users alike, ensuring the safe and reliable operation of Claude Code.

Summary of the Bug

The essence of this bug lies in the Task tool's ability to circumvent Plan Mode's write restrictions. Plan Mode, designed to prevent any write operations, is a crucial safety feature. However, agents initiated through the Task tool can still write files, effectively bypassing this safeguard. This discrepancy poses a significant security risk, as it undermines the fundamental purpose of Plan Mode and can lead to unintended consequences. The core issue is that agents spawned by the Task tool operate in a separate context, failing to inherit the Plan Mode restrictions from the parent session. This allows these child agents to have their own tool permissions, which are not constrained by the parent's Plan Mode state. This article will explore the critical nature of this vulnerability and discuss why it needs immediate attention and resolution.

Severity: A Critical Security Issue

The severity of this bug cannot be overstated. It is classified as CRITICAL due to its potential to compromise the integrity of the file system and the trust users place in Plan Mode. This vulnerability undermines the core safety guarantee that Plan Mode provides, making it a top priority for resolution. The ability of agents to bypass write restrictions means that unintended file modifications, data overwrites, and even security breaches are possible. For users who rely on Plan Mode to review changes before execution, this bug represents a significant risk. Understanding the severity of this issue is the first step in addressing it effectively and ensuring that the software operates as intended.

Environment and Context

This bug was identified in a specific environment, providing valuable context for understanding its scope and impact:

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

This information helps to narrow down the conditions under which the bug occurs, aiding in its replication and resolution. By knowing the specific version, model, platform, and date, developers can focus their efforts on the relevant areas of the codebase and system architecture. This detailed context is essential for efficient debugging and ensures that the fix is tailored to the environment where the vulnerability was discovered.

Steps to Reproduce the Bug

To fully grasp the nature of this bug and its impact, it is essential to understand the steps required to reproduce it. By following these steps, developers and users can verify the bug's existence and ensure that the fix effectively addresses the issue.

  1. Start Claude Code in a directory: This sets the initial environment for the test.
  2. Enter Plan Mode using shift+tab: This activates the safety feature that should prevent write operations.
  3. While in Plan Mode, invoke any agent via the Task tool that has write capabilities (e.g., documentation-specialist): This is the crucial step that triggers the bug.
  4. The agent will successfully write files despite Plan Mode being active: This confirms the bypass of the write restrictions.

These steps clearly demonstrate how the bug can be triggered, highlighting the vulnerability in the interaction between Plan Mode and the Task tool. Understanding these steps is crucial for both testing the fix and educating users about the bug's behavior.

Expected vs. Actual Behavior

To fully appreciate the severity of this bug, it's important to contrast the expected behavior with the actual behavior. This comparison underscores the deviation from the intended functionality and highlights the potential risks.

Expected Behavior

  • When Plan Mode is active, ALL write operations should be blocked.
  • This includes writes from agents invoked via the Task tool.
  • Any attempt to write files should fail with an appropriate error message.

Actual Behavior

  • Plan Mode correctly prevents direct Write/Edit tool usage by the main assistant.
  • However, agents invoked via the Task tool can still write files.
  • No error or warning is provided about this bypass.

This discrepancy between expected and actual behavior clearly illustrates the vulnerability. The failure to block write operations from Task-invoked agents undermines the fundamental safety mechanism of Plan Mode. This can lead to unexpected file modifications, data corruption, and a breach of user trust. Understanding this contrast is vital for emphasizing the importance of a swift and effective resolution.

Evidence of the Bug

Concrete evidence supports the existence and impact of this bug. A specific session ID and timestamp provide a detailed record of the bug's occurrence:

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

Sequence of events:

  1. 17:14:28 - Started working in plan mode (never exited until 17:31)
  2. 17:19:40 - Invoked documentation-specialist agent 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 - Finally exited Plan Mode with ExitPlanMode tool

This sequence of events clearly demonstrates how the documentation-specialist agent was able to create a file while Plan Mode was active. This concrete evidence reinforces the severity of the bug and the need for a prompt fix. The detailed timestamp and session ID provide a verifiable record of the vulnerability in action.

Impact of the Bug

The impact of this bug extends beyond mere inconvenience; it poses significant risks to security, user trust, and data safety. Understanding these impacts is crucial for prioritizing the bug fix and implementing effective mitigation strategies.

  • Security Risk: Plan Mode is designed as a safety mechanism to prevent unintended file system modifications. This bug undermines this mechanism, creating a security vulnerability.
  • User Trust: Users rely on Plan Mode to review changes before execution. The bug erodes this trust by allowing unintended actions to occur.
  • Data Safety: Unintended writes could modify or overwrite important files, leading to data loss or corruption.

The potential for security breaches, loss of user trust, and data corruption makes this bug a high-priority issue. Addressing these impacts requires a comprehensive solution that not only fixes the immediate vulnerability but also reinforces the overall safety and reliability of the system.

Root Cause Analysis

A thorough root cause analysis is essential for understanding why this bug occurred and how to prevent similar issues in the future. The analysis reveals that the Task tool spawns agents in a separate context that doesn't inherit Plan Mode restrictions from the parent session. These child agents have their own tool permissions that aren't constrained by the parent's Plan Mode state.

This explains why agents invoked via the Task tool can bypass Plan Mode restrictions. The issue stems from the lack of proper propagation of Plan Mode state to child agents. To address this, the system needs to ensure that all tool invocations, including those from nested or child agents, respect the Plan Mode state of the root session. A comprehensive fix should include explicit Plan Mode state propagation to all agent invocations.

Suggested Fixes

Based on the root cause analysis, several fixes are suggested to address the bug and prevent its recurrence. These fixes range from immediate actions to comprehensive solutions, ensuring a multi-faceted approach to resolving the vulnerability.

  1. Immediate: The Task tool should check the parent session's Plan Mode state before allowing child agents to perform write operations. This provides an immediate safeguard against the bug's exploitation.
  2. Comprehensive: All tool invocations (including nested/child agent calls) should respect the Plan Mode state of the root session. This ensures consistent behavior across the system.
  3. Safety Check: Add explicit Plan Mode state propagation to all agent invocations. This reinforces the intended behavior and prevents future bypasses.

Implementing these fixes will not only resolve the immediate issue but also strengthen the overall safety and security of Claude Code. The combination of immediate and comprehensive measures ensures a robust solution.

Workarounds

Until a permanent fix is implemented, users can employ several workarounds to mitigate the risk posed by this bug. These workarounds provide temporary relief and minimize the potential for unintended consequences.

  • Avoid using the Task tool while in Plan Mode. This prevents the bug from being triggered.
  • Be aware that Plan Mode does NOT currently prevent writes from Task-invoked agents. This knowledge helps users to be more cautious.
  • Manually verify that no unintended files were created after using agents in Plan Mode. This ensures that any unauthorized changes are detected and addressed promptly.

By following these workarounds, users can reduce their exposure to the bug's impact until a comprehensive fix is available. These temporary measures are essential for maintaining data integrity and user trust.

Additional Context and Reproducibility

Further context and reproducibility information reinforce the validity and consistency of the bug report. The file IMPLEMENTATION_ROADMAP.md (13,491 bytes) was created at 10:20 AM while the assistant was in Plan Mode. This file creation was not requested by the user and violated the Plan Mode contract. The bug's reproducibility is 100%, meaning that it consistently occurs under the specified conditions. This high reproducibility underscores the bug's significance and the need for a prompt resolution.

Priority and Conclusion

Given its impact on security, user trust, and data safety, this bug should be treated as a P0/P1 issue. This classification signifies the highest level of priority, demanding immediate attention and resolution. The vulnerability compromises the fundamental safety guarantee of Plan Mode, making it imperative to address it as quickly as possible. This article has detailed the bug's nature, impact, and suggested fixes, providing a comprehensive understanding of the issue and the steps required to resolve it effectively.

In conclusion, the Task Tool Agents bypassing Plan Mode Write Restrictions bug poses a significant threat to the integrity and security of Claude Code. By understanding the bug's nature, impact, and suggested fixes, developers and users can work together to ensure a swift and effective resolution. Prioritizing this issue is essential for maintaining user trust and safeguarding data safety.

For further reading on software security best practices, consider exploring resources like the OWASP Foundation.