This document should guide you about understanding the security concept behind Arena and also where the boundaries are.

In general Arena is a coding agent that runs locally within the security boundary of the user that is running it. It's the responsibility of the user to monitor its operations or to contain it within a container, virtual machine or other Sandbox solution.

Arena treats the local user account and files writable by that account as inside the same trust boundary as the Arena process itself. If an attacker can modify files under the user's home directory, workspace, shell startup files, environment, or Arena configuration, they can generally influence Arena or other local developer tools. Reports that depend on such prior local write access are not security vulnerabilities unless they demonstrate how Arena grants that write access or crosses an operating-system privilege boundary.

Arena relies on users installing trustworthy extensions and loading trustworthy skills and only to use arena within trusted repositories. This is because files like AGENTS.md or instructions in comments can be used to prompt inject the coding agent trivially and this cannot be protected against.

If you believe you found a security vulnerability in arena or another package in this repository, please report it privately by either:

• Emailing security@earendil.com, or
• Opening a private report through GitHub Security Advisories for this repository

Please include:

• A description of the issue and its impact
• Steps to reproduce, proof of concept, or relevant logs
• Affected package, version, commit, or configuration
• Any known mitigations

Do not open a public issue for security-sensitive reports. We will review reports and coordinate disclosure as appropriate.

Security issues in the distributed packages, command-line tools, APIs, and repository code are in scope as well as earendil operated infrastructure on arena.dev.

• Local code execution or sandboxing behavior (the Arena coding agent intentionally does not have a sandbox)
• Behavior of arena extensions or skills installed by the user
• Risks from working in untrusted repositories
• Risks from installing untrusted extensions, skills, packages, or tools
• Isuses caused by non trustworthy MITM proxies
• Public internet exposure of a Arena installation
• Prompt injection attacks
• Exposed secrets that are third-party/user-controlled credentials
• Reports requiring the ability to create, modify, delete, or replace files, directories, symlinks, environment variables, shell configuration, or other user-controlled local state on the target machine. This includes ~/.arena, ~/.arena/agent/models.json, workspace files, AGENTS.md, skills, extensions, extension configuration, dotfiles, and files synchronized through NFS, roaming profiles, or dotfile managers, unless the report shows how Arena itself grants that access.
• Issues caused by intentionally weakened user configuration.
• Resource/DOS claims that require trusted local input/config against the arena coding agent.
• Reports about malicious model output.
• User-approved or user-initiated local actions presented as vulnerabilities.

The most useful reports show a current, reproducible security boundary bypass with demonstrated impact. Reports that only show expected local-agent behavior, prompt injection, or a malicious trusted extension/skill are not security vulnerabilities under this model.

For example, a report showing that malicious contents written to a trusted Arena configuration file cause Arena to execute commands, load attacker-controlled tools, send credentials to an attacker-controlled endpoint, or otherwise change behavior is out of scope.

When possible, include the exact affected path, package version or commit SHA, configuration, and a proof of concept against the latest release or latest main. For dependency reports, include evidence that the shipped dependency is affected and that the issue is reachable through Arena. For exposed-secret reports, include evidence that the credential is owned by Earendil or grants access to Earendil-operated infrastructure or services.