Bug: Agent Tool Restrictions Ignored, Full Access Granted

Nov 21, 2025 by Alex Johnson 58 views

Introduction

In this article, we will discuss a critical bug encountered in custom agent configurations where tool restrictions are not being enforced. This means that agents, regardless of their intended limitations, have full access to all available tools. This issue undermines the principle of least privilege and compromises the intended design of specialized agents. We will delve into the specifics of the bug, how to reproduce it, the expected behavior versus the actual behavior, and the implications of this issue. Understanding and addressing this bug is crucial for maintaining the integrity and security of agent-based systems.

Environment

Before diving into the bug specifics, let's outline the environment in which this issue was observed. The reported bug can manifest across various platforms, including Anthropic API, AWS Bedrock, Google Vertex AI, and potentially other platforms. The Claude CLI version and the operating system in use are also relevant factors. For instance, the bug has been observed on macOS 14.3, Windows 11, and Ubuntu 22.04, using terminals like iTerm2 and the standard Terminal App. This broad range of environments suggests that the bug is not platform-specific but rather lies within the core logic of how tool restrictions are enforced (or not enforced) within the agent system. This makes addressing the bug all the more critical to ensure consistent behavior across different setups.

Bug Description

The core issue is that custom agents are not adhering to the tool restrictions defined in their configurations. An agent configured to have access to a limited set of tools can, in practice, utilize any tool available within the system. This behavior directly contradicts the intended design, where specialized agents should only have the necessary permissions to perform their designated tasks. The unintended access can lead to several problems, including security vulnerabilities, operational inefficiencies, and a breakdown of the agent orchestration strategy. Imagine a scenario where an agent designed solely for routing tasks is able to execute arbitrary code or access sensitive data. This is precisely the risk posed by this bug.

Steps to Reproduce

To reproduce the bug, follow these steps:

Create a custom agent configuration file. For example, create a file named jarvis.md within the .claude/agents/ directory. This file will define the agent's properties, including its name, description, and tool restrictions.
Define the agent's configuration with restricted tool access. Here's an example configuration:
```
name: jarvis
description: Routes user requests to appropriate specialized agents
tools: Task  # Should restrict to ONLY Task tool
model: opus
```
This configuration specifies that the agent named "jarvis" should only have access to the "Task" tool. The intention is to limit this agent's capabilities to routing tasks to other specialized agents.
Invoke the agent using @agent-jarvis or through the Task tool. This triggers the agent to process the incoming request.
Observe the agent's behavior. The bug manifests when the agent executes with full tool access, ignoring the specified restrictions.

By following these steps, you can consistently reproduce the bug and verify that the tool restrictions are not being enforced as expected. This reproducibility is crucial for debugging and implementing a fix.

Expected Behavior

The expected behavior is that an agent configured with specific tool restrictions should only be able to utilize the tools listed in its configuration. In the example provided, the "jarvis" agent, configured with tools: Task, should only be able to use the Task tool. Any attempt to use other tools, such as Read, Bash, Grep, or Write, should result in a permission error. This is a fundamental aspect of the principle of least privilege, where agents are granted only the necessary permissions to perform their duties. Furthermore, the agent should be forced to delegate work to other agents via the Task tool, ensuring that it functions as an orchestrator rather than a direct executor of tasks.

Actual Behavior

However, the actual behavior observed is quite different. Agents configured with tool restrictions can use all available tools, effectively bypassing the intended limitations. In the "jarvis" example, despite being configured with tools: Task, the agent can freely use Read, Bash, Grep, Write, and other tools. This means the agent can perform work directly instead of routing tasks through specialized agents, defeating the purpose of having a dedicated orchestrator. The tool restrictions specified in the agent configuration are completely ignored, leading to a significant deviation from the expected behavior. This discrepancy highlights the severity of the bug and its potential impact on the system's functionality and security.

Additional Context

This bug violates the principle of least privilege and negates the benefits of having specialized agents with limited capabilities. For instance, a routing or orchestrator agent like "jarvis," which should only coordinate other agents, can perform all operations directly. This bypasses the intended design of a pure orchestrator, which is meant to delegate tasks rather than execute them. The configuration file example below illustrates the intended restriction:

name: jarvis
description: Routes user requests to appropriate specialized agents
tools: Task  # Should restrict to ONLY Task tool
model: opus

Despite the tools: Task configuration, the observed behavior is that the agent can execute Bash commands, read files, and perform other operations that should be restricted. This unrestricted access undermines the purpose of having specialized agents with defined roles and responsibilities. The implications of this bug extend beyond mere inconvenience; it poses a risk to the overall security and efficiency of the agent-based system. Addressing this issue is critical to ensure that agents operate within their intended boundaries and that the system functions as designed.

Impact and Implications

The implications of this bug are far-reaching and can significantly impact the security, efficiency, and maintainability of the system. When agents have unrestricted access to tools, it creates security vulnerabilities. A compromised agent can potentially access sensitive data, execute arbitrary code, or perform other malicious activities. This is especially concerning in systems where agents interact with critical infrastructure or handle confidential information. Furthermore, the bug undermines the principle of least privilege, which is a fundamental security best practice. By granting agents only the necessary permissions, the attack surface is reduced, and the potential damage from a breach is limited.

From an efficiency standpoint, the bug can lead to suboptimal performance. When routing agents can directly execute tasks, it bypasses the intended orchestration strategy. This can result in tasks being handled by agents that are not best suited for the job, leading to delays and inefficiencies. Additionally, the lack of enforced tool restrictions makes the system harder to maintain and debug. When agents can behave unpredictably, it becomes challenging to trace the root cause of issues and ensure that the system functions correctly. The intended architecture, with specialized agents and clear boundaries, is compromised, making it difficult to reason about the system's behavior. Therefore, addressing this bug is crucial for maintaining the integrity and reliability of the agent-based system.

Potential Causes

Several factors could be contributing to this bug. One potential cause is a flaw in the access control mechanism. The system might not be correctly checking and enforcing the tool restrictions defined in the agent configurations. This could be due to a coding error, a misconfiguration, or a design flaw in the access control logic. Another possibility is an issue with how the agent configurations are being parsed and interpreted. If the system fails to correctly read and process the tools: setting, it might default to granting full access to all tools. This could be caused by a parsing error, a schema validation issue, or an incompatibility between the configuration format and the system's parser.

Additionally, the bug could be related to the agent initialization process. If the agent's toolset is not being properly initialized based on the configuration, it might inherit default permissions that grant access to all tools. This could be a result of a race condition, an incorrect initialization sequence, or a missing step in the agent setup process. Finally, a caching issue could also be to blame. If the system is caching agent configurations, it might be using outdated or incorrect information when enforcing tool restrictions. This could happen if the cache is not being properly invalidated when agent configurations are updated. Identifying the root cause of the bug is essential for implementing an effective fix.

Proposed Solutions and Workarounds

To address this bug, several solutions and workarounds can be considered. The most direct solution is to fix the underlying issue in the access control mechanism. This involves carefully reviewing the code responsible for enforcing tool restrictions and identifying any flaws or errors. The fix might involve correcting the logic for checking permissions, ensuring that agent configurations are properly parsed and interpreted, and verifying that the agent's toolset is correctly initialized. Implementing unit tests and integration tests can help ensure that the fix is effective and does not introduce new issues.

Another approach is to implement a workaround that provides an additional layer of access control. This could involve creating a wrapper or proxy around the agent execution environment that explicitly checks tool permissions before allowing an agent to use a tool. This workaround can serve as a temporary solution while the underlying bug is being addressed. Additionally, improving logging and monitoring can help detect and mitigate the impact of the bug. By logging tool usage and monitoring agent behavior, it becomes easier to identify instances where agents are exceeding their intended permissions. This can allow for proactive intervention and prevent potential security breaches. Ultimately, a comprehensive solution that addresses the root cause of the bug is essential for ensuring the long-term security and reliability of the system.

Conclusion

The bug where custom agent tool restrictions are not enforced poses a significant risk to the security and integrity of agent-based systems. The ability for agents to bypass intended limitations and access all available tools undermines the principle of least privilege and can lead to various problems, including security vulnerabilities and operational inefficiencies. By understanding the specifics of the bug, how to reproduce it, and its implications, developers and system administrators can take steps to mitigate the risk and implement effective solutions. Addressing this issue is crucial for maintaining the trust and reliability of agent-based systems and ensuring that they function as designed.

For more information on security best practices, visit the OWASP Foundation website.