Security

Hermes Agent is designed with a defense-in-depth security model. This page covers every security boundary — from command approval to container isolation to user authorization on messaging platforms.

Overview​

The security model has five layers:

1. User authorization — who can talk to the agent (allowlists, DM pairing)
2. Dangerous command approval — human-in-the-loop for destructive operations
3. Container isolation — Docker/Singularity/Modal sandboxing with hardened settings
4. MCP credential filtering — environment variable isolation for MCP subprocesses
5. Context file scanning — prompt injection detection in project files

Dangerous Command Approval​

Before executing any command, Hermes checks it against a curated list of dangerous patterns. If a match is found, the user must explicitly approve it.

Approval Modes​

The approval system supports three modes, configured via approvals.mode in ~/.hermes/config.yaml:

approvals:
  mode: manual    # manual | smart | off
  timeout: 60     # seconds to wait for user response (default: 60)

YOLO Mode​

YOLO mode bypasses all dangerous command approval prompts for the current session. It can be activated three ways:

1. CLI flag: Start a session with hermes --yolo or hermes chat --yolo
2. Slash command: Type /yolo during a session to toggle it on/off
3. Environment variable: Set HERMES_YOLO_MODE=1

The /yolo command is a toggle — each use flips the mode on or off:

> /yolo
  ⚡ YOLO mode ON — all commands auto-approved. Use with caution.

> /yolo
  ⚠ YOLO mode OFF — dangerous commands will require approval.

YOLO mode is available in both CLI and gateway sessions. Internally, it sets the HERMES_YOLO_MODE environment variable which is checked before every command execution.

Approval Timeout​

When a dangerous command prompt appears, the user has a configurable amount of time to respond. If no response is given within the timeout, the command is denied by default (fail-closed).

Configure the timeout in ~/.hermes/config.yaml:

approvals:
  timeout: 60  # seconds (default: 60)

What Triggers Approval​

The following patterns trigger approval prompts (defined in tools/approval.py):

Approval Flow (CLI)​

In the interactive CLI, dangerous commands show an inline approval prompt:

  ⚠️  DANGEROUS COMMAND: recursive delete
      rm -rf /tmp/old-project

      [o]nce  |  [s]ession  |  [a]lways  |  [d]eny

      Choice [o/s/a/D]:

The four options:

• once — allow this single execution
• session — allow this pattern for the rest of the session
• always — add to permanent allowlist (saved to config.yaml)
• deny (default) — block the command

Approval Flow (Gateway/Messaging)​

On messaging platforms, the agent sends the dangerous command details to the chat and waits for the user to reply:

• Reply yes, y, approve, ok, or go to approve
• Reply no, n, deny, or cancel to deny

The HERMES_EXEC_ASK=1 environment variable is automatically set when running the gateway.

Permanent Allowlist​

Commands approved with "always" are saved to ~/.hermes/config.yaml:

# Permanently allowed dangerous command patterns
command_allowlist:
  - rm
  - systemctl

These patterns are loaded at startup and silently approved in all future sessions.

User Authorization (Gateway)​

When running the messaging gateway, Hermes controls who can interact with the bot through a layered authorization system.

Authorization Check Order​

The _is_user_authorized() method checks in this order:

1. Per-platform allow-all flag (e.g., DISCORD_ALLOW_ALL_USERS=true)
2. DM pairing approved list (users approved via pairing codes)
3. Platform-specific allowlists (e.g., TELEGRAM_ALLOWED_USERS=12345,67890)
4. Global allowlist (GATEWAY_ALLOWED_USERS=12345,67890)
5. Global allow-all (GATEWAY_ALLOW_ALL_USERS=true)
6. Default: deny

Platform Allowlists​

Set allowed user IDs as comma-separated values in ~/.hermes/.env:

# Platform-specific allowlists
TELEGRAM_ALLOWED_USERS=123456789,987654321
DISCORD_ALLOWED_USERS=111222333444555666
WHATSAPP_ALLOWED_USERS=15551234567
SLACK_ALLOWED_USERS=U01ABC123

# Cross-platform allowlist (checked for all platforms)
GATEWAY_ALLOWED_USERS=123456789

# Per-platform allow-all (use with caution)
DISCORD_ALLOW_ALL_USERS=true

# Global allow-all (use with extreme caution)
GATEWAY_ALLOW_ALL_USERS=true

No user allowlists configured. All unauthorized users will be denied.
Set GATEWAY_ALLOW_ALL_USERS=true in ~/.hermes/.env to allow open access,
or configure platform allowlists (e.g., TELEGRAM_ALLOWED_USERS=your_id).

DM Pairing System​

For more flexible authorization, Hermes includes a code-based pairing system. Instead of requiring user IDs upfront, unknown users receive a one-time pairing code that the bot owner approves via the CLI.

How it works:

1. An unknown user sends a DM to the bot
2. The bot replies with an 8-character pairing code
3. The bot owner runs hermes pairing approve <platform> <code> on the CLI
4. The user is permanently approved for that platform

Control how unauthorized direct messages are handled in ~/.hermes/config.yaml:

unauthorized_dm_behavior: pair

whatsapp:
  unauthorized_dm_behavior: ignore

• pair is the default. Unauthorized DMs get a pairing code reply.
• ignore silently drops unauthorized DMs.
• Platform sections override the global default, so you can keep pairing on Telegram while keeping WhatsApp silent.

Security features (based on OWASP + NIST SP 800-63-4 guidance):

Pairing CLI commands:

# List pending and approved users
hermes pairing list

# Approve a pairing code
hermes pairing approve telegram ABC12DEF

# Revoke a user's access
hermes pairing revoke telegram 123456789

# Clear all pending codes
hermes pairing clear-pending

Storage: Pairing data is stored in ~/.hermes/pairing/ with per-platform JSON files:

• {platform}-pending.json — pending pairing requests
• {platform}-approved.json — approved users
• _rate_limits.json — rate limit and lockout tracking

Container Isolation​

When using the docker terminal backend, Hermes applies strict security hardening to every container.

Docker Security Flags​

Every container runs with these flags (defined in tools/environments/docker.py):

_SECURITY_ARGS = [
    "--cap-drop", "ALL",                          # Drop ALL Linux capabilities
    "--security-opt", "no-new-privileges",         # Block privilege escalation
    "--pids-limit", "256",                         # Limit process count
    "--tmpfs", "/tmp:rw,nosuid,size=512m",         # Size-limited /tmp
    "--tmpfs", "/var/tmp:rw,noexec,nosuid,size=256m",  # No-exec /var/tmp
    "--tmpfs", "/run:rw,noexec,nosuid,size=64m",   # No-exec /run
]

Resource Limits​

Container resources are configurable in ~/.hermes/config.yaml:

terminal:
  backend: docker
  docker_image: "nikolaik/python-nodejs:python3.11-nodejs20"
  docker_forward_env: []  # Explicit allowlist only; empty keeps secrets out of the container
  container_cpu: 1        # CPU cores
  container_memory: 5120  # MB (default 5GB)
  container_disk: 51200   # MB (default 50GB, requires overlay2 on XFS)
  container_persistent: true  # Persist filesystem across sessions

Filesystem Persistence​

• Persistent mode (container_persistent: true): Bind-mounts /workspace and /root from ~/.hermes/sandboxes/docker/<task_id>/
• Ephemeral mode (container_persistent: false): Uses tmpfs for workspace — everything is lost on cleanup

Terminal Backend Security Comparison​

Environment Variable Passthrough​

Both execute_code and terminal strip sensitive environment variables from child processes to prevent credential exfiltration by LLM-generated code. However, skills that declare required_environment_variables legitimately need access to those vars.

How It Works​

Two mechanisms allow specific variables through the sandbox filters:

1. Skill-scoped passthrough (automatic)

When a skill is loaded (via skill_view or the /skill command) and declares required_environment_variables, any of those vars that are actually set in the environment are automatically registered as passthrough. Missing vars (still in setup-needed state) are not registered.

# In a skill's SKILL.md frontmatter
required_environment_variables:
  - name: TENOR_API_KEY
    prompt: Tenor API key
    help: Get a key from https://developers.google.com/tenor

After loading this skill, TENOR_API_KEY passes through to execute_code, terminal (local), and remote backends (Docker, Modal) — no manual configuration needed.

2. Config-based passthrough (manual)

For env vars not declared by any skill, add them to terminal.env_passthrough in config.yaml:

terminal:
  env_passthrough:
    - MY_CUSTOM_KEY
    - ANOTHER_TOKEN

Credential File Passthrough (OAuth tokens, etc.)​

Some skills need files (not just env vars) in the sandbox — for example, Google Workspace stores OAuth tokens as google_token.json in ~/.hermes/. Skills declare these in frontmatter:

required_credential_files:
  - path: google_token.json
    description: Google OAuth2 token (created by setup script)
  - path: google_client_secret.json
    description: Google OAuth2 client credentials

When loaded, Hermes checks if these files exist in ~/.hermes/ and registers them for mounting:

• Docker: Read-only bind mounts (-v host:container:ro)
• Modal: Mounted at sandbox creation + synced before each command (handles mid-session OAuth setup)
• Local: No action needed (files already accessible)

You can also list credential files manually in config.yaml:

terminal:
  credential_files:
    - google_token.json
    - my_custom_oauth_token.json

Paths are relative to ~/.hermes/. Files are mounted to /root/.hermes/ inside the container.

What Each Sandbox Filters​

Security Considerations​

• The passthrough only affects vars you or your skills explicitly declare — the default security posture is unchanged for arbitrary LLM-generated code
• Credential files are mounted read-only into Docker containers
• Skills Guard scans skill content for suspicious env access patterns before installation
• Missing/unset vars are never registered (you can't leak what doesn't exist)
• Hermes infrastructure secrets (provider API keys, gateway tokens) should never be added to env_passthrough — they have dedicated mechanisms

MCP Credential Handling​

MCP (Model Context Protocol) server subprocesses receive a filtered environment to prevent accidental credential leakage.

Safe Environment Variables​

Only these variables are passed through from the host to MCP stdio subprocesses:

PATH, HOME, USER, LANG, LC_ALL, TERM, SHELL, TMPDIR

Plus any XDG_* variables. All other environment variables (API keys, tokens, secrets) are stripped.

Variables explicitly defined in the MCP server's env config are passed through:

mcp_servers:
  github:
    command: "npx"
    args: ["-y", "@modelcontextprotocol/server-github"]
    env:
      GITHUB_PERSONAL_ACCESS_TOKEN: "ghp_..."  # Only this is passed

Credential Redaction​

Error messages from MCP tools are sanitized before being returned to the LLM. The following patterns are replaced with [REDACTED]:

• GitHub PATs (ghp_...)
• OpenAI-style keys (sk-...)
• Bearer tokens
• token=, key=, API_KEY=, password=, secret= parameters

Website Access Policy​

You can restrict which websites the agent can access through its web and browser tools. This is useful for preventing the agent from accessing internal services, admin panels, or other sensitive URLs.

# In ~/.hermes/config.yaml
security:
  website_blocklist:
    enabled: true
    domains:
      - "*.internal.company.com"
      - "admin.example.com"
    shared_files:
      - "/etc/hermes/blocked-sites.txt"

When a blocked URL is requested, the tool returns an error explaining the domain is blocked by policy. The blocklist is enforced across web_search, web_extract, browser_navigate, and all URL-capable tools.

See Website Blocklist in the configuration guide for full details.

SSRF Protection​

All URL-capable tools (web search, web extract, vision, browser) validate URLs before fetching them to prevent Server-Side Request Forgery (SSRF) attacks. Blocked addresses include:

• Private networks (RFC 1918): 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
• Loopback: 127.0.0.0/8, ::1
• Link-local: 169.254.0.0/16 (includes cloud metadata at 169.254.169.254)
• CGNAT / shared address space (RFC 6598): 100.64.0.0/10 (Tailscale, WireGuard VPNs)
• Cloud metadata hostnames: metadata.google.internal, metadata.goog
• Reserved, multicast, and unspecified addresses

SSRF protection is always active and cannot be disabled. DNS failures are treated as blocked (fail-closed). Redirect chains are re-validated at each hop to prevent redirect-based bypasses.

Tirith Pre-Exec Security Scanning​

Hermes integrates tirith for content-level command scanning before execution. Tirith detects threats that pattern matching alone misses:

• Homograph URL spoofing (internationalized domain attacks)
• Pipe-to-interpreter patterns (curl | bash, wget | sh)
• Terminal injection attacks

Tirith auto-installs from GitHub releases on first use with SHA-256 checksum verification (and cosign provenance verification if cosign is available).

# In ~/.hermes/config.yaml
security:
  tirith_enabled: true       # Enable/disable tirith scanning (default: true)
  tirith_path: "tirith"      # Path to tirith binary (default: PATH lookup)
  tirith_timeout: 5          # Subprocess timeout in seconds
  tirith_fail_open: true     # Allow execution when tirith is unavailable (default: true)

When tirith_fail_open is true (default), commands proceed if tirith is not installed or times out. Set to false in high-security environments to block commands when tirith is unavailable.

Tirith's verdict integrates with the approval flow: safe commands pass through, while both suspicious and blocked commands trigger user approval with the full tirith findings (severity, title, description, safer alternatives). Users can approve or deny — the default choice is deny to keep unattended scenarios secure.

Context File Injection Protection​

Context files (AGENTS.md, .cursorrules, SOUL.md) are scanned for prompt injection before being included in the system prompt. The scanner checks for:

• Instructions to ignore/disregard prior instructions
• Hidden HTML comments with suspicious keywords
• Attempts to read secrets (.env, credentials, .netrc)
• Credential exfiltration via curl
• Invisible Unicode characters (zero-width spaces, bidirectional overrides)

Blocked files show a warning:

[BLOCKED: AGENTS.md contained potential prompt injection (prompt_injection). Content not loaded.]

Best Practices for Production Deployment​

Gateway Deployment Checklist​

1. Set explicit allowlists — never use GATEWAY_ALLOW_ALL_USERS=true in production
2. Use container backend — set terminal.backend: docker in config.yaml
3. Restrict resource limits — set appropriate CPU, memory, and disk limits
4. Store secrets securely — keep API keys in ~/.hermes/.env with proper file permissions
5. Enable DM pairing — use pairing codes instead of hardcoding user IDs when possible
6. Review command allowlist — periodically audit command_allowlist in config.yaml
7. Set MESSAGING_CWD — don't let the agent operate from sensitive directories
8. Run as non-root — never run the gateway as root
9. Monitor logs — check ~/.hermes/logs/ for unauthorized access attempts
10. Keep updated — run hermes update regularly for security patches

Securing API Keys​

# Set proper permissions on the .env file
chmod 600 ~/.hermes/.env

# Keep separate keys for different services
# Never commit .env files to version control

Network Isolation​

For maximum security, run the gateway on a separate machine or VM:

terminal:
  backend: ssh
  ssh_host: "agent-worker.local"
  ssh_user: "hermes"
  ssh_key: "~/.ssh/hermes_agent_key"

This keeps the gateway's messaging connections separate from the agent's command execution.