<!-- mcp-name: io.github.behrensd/mcpwall -->
# mcpwall
[](https://www.npmjs.com/package/mcpwall)
[](https://github.com/behrensd/mcp-firewall/actions/workflows/ci.yml)
[](https://nodejs.org)
[](./LICENSE)
<a href="https://glama.ai/mcp/servers/@behrensd/mcpwall"><img width="380" height="200" src="https://glama.ai/mcp/servers/@behrensd/mcpwall/badge" alt="mcpwall MCP server" /></a>
**iptables for MCP.** Blocks dangerous tool calls, scans for secret leakage, logs everything. No AI, no cloud, pure rules.
Sits between your AI coding tool (Claude Code, Cursor, Windsurf) and MCP servers, intercepting every JSON-RPC message and enforcing YAML-defined policies.
<p align="center">
<img src="demo/demo.gif" alt="mcpwall demo — blocking SSH key theft, pipe-to-shell, and secret leakage" width="700">
</p>
## Why
MCP servers have full access to your filesystem, shell, databases, and APIs. When an AI agent calls `tools/call`, the server executes whatever the agent asks — reading SSH keys, running `rm -rf`, exfiltrating secrets. There's no built-in policy layer.
mcpwall adds one. It's a transparent stdio proxy that:
- **Blocks sensitive file access** — `.ssh/`, `.env`, credentials, browser data
- **Blocks dangerous commands** — `rm -rf`, pipe-to-shell, reverse shells
- **Scans for secret leakage** — API keys, tokens, private keys (regex + entropy)
- **Scans server responses** — redacts leaked secrets, blocks prompt injection patterns, flags suspicious content
- **Logs everything** — JSON Lines audit trail of every tool call and response
- **Uses zero AI** — deterministic rules, no LLM decisions, no cloud calls
## Install
```bash
npm install -g mcpwall
```
Or use directly with npx:
```bash
npx mcpwall -- npx -y @modelcontextprotocol/server-filesystem /path/to/dir
```
## Quick Start
### Option 1: Docker MCP Toolkit
If you use [Docker MCP Toolkit](https://docs.docker.com/ai/mcp-catalog-and-toolkit/toolkit/) (the most common setup), change your MCP config from:
```json
{
"mcpServers": {
"MCP_DOCKER": {
"command": "docker",
"args": ["mcp", "gateway", "run"]
}
}
}
```
To:
```json
{
"mcpServers": {
"MCP_DOCKER": {
"command": "npx",
"args": ["-y", "mcpwall", "--", "docker", "mcp", "gateway", "run"]
}
}
}
```
That's it. mcpwall now sits in front of all your Docker MCP servers, logging every tool call and blocking dangerous ones. No config file needed — sensible defaults apply automatically.
### Option 2: Interactive setup
```bash
npx mcpwall init
```
This finds your existing MCP servers in Claude Code, Cursor, Windsurf, and VS Code configs and wraps them.
### Option 3: Manual wrapping (any MCP server)
Change your MCP config from:
```json
{
"mcpServers": {
"filesystem": {
"command": "npx",
"args": ["-y", "@modelcontextprotocol/server-filesystem", "/Users/me/projects"]
}
}
}
```
To:
```json
{
"mcpServers": {
"filesystem": {
"command": "npx",
"args": [
"-y", "mcpwall", "--",
"npx", "-y", "@modelcontextprotocol/server-filesystem", "/Users/me/projects"
]
}
}
}
```
### Option 4: Wrap a specific server
```bash
npx mcpwall wrap filesystem
```
## How It Works
```
┌──────────────┐ stdio ┌──────────────┐ stdio ┌──────────────┐
│ Claude Code │ ──────────▶ │ mcpwall │ ──────────▶ │ Real MCP │
│ (MCP Host) │ ◀────────── │ (proxy) │ ◀────────── │ Server │
└──────────────┘ └──────────────┘ └──────────────┘
▲ Inbound rules │
│ (block dangerous requests) │
│ │
└── Outbound rules ◀───────────┘
(redact secrets, block injection)
```
**Inbound** (requests):
1. Intercepts every JSON-RPC request on stdin
2. Parses `tools/call` requests — extracts tool name and arguments
3. Walks rules top-to-bottom, first match wins
4. **Allow**: forward to real server
5. **Deny**: return JSON-RPC error to host, log, do not forward
**Outbound** (responses):
1. Parses every response from the server before forwarding
2. Evaluates against `outbound_rules` (same first-match-wins semantics)
3. **Allow**: forward unchanged
4. **Deny**: replace response with blocked message
5. **Redact**: surgically replace secrets with `[REDACTED BY MCPWALL]`, forward modified response
6. **Log only**: forward unchanged, log the match
## Configuration
Config is YAML. mcpwall looks for:
1. `~/.mcpwall/config.yml` (global)
2. `.mcpwall.yml` (project, overrides global)
If neither exists, built-in default rules apply.
### Example config
```yaml
version: 1
settings:
log_dir: ~/.mcpwall/logs
log_level: info # debug | info | warn | error
default_action: allow # allow | deny | ask
rules:
# Block reading SSH keys
- name: block-ssh-keys
match:
method: tools/call
tool: "*"
arguments:
_any_value:
regex: "(\\.ssh/|id_rsa|id_ed25519)"
action: deny
message: "Blocked: access to SSH keys"
# Block dangerous shell commands
- name: block-dangerous-commands
match:
method: tools/call
tool: "*"
arguments:
_any_value:
regex: "(rm\\s+-rf|curl.*\\|.*bash)"
action: deny
message: "Blocked: dangerous command"
# Block writes outside project directory
- name: block-external-writes
match:
method: tools/call
tool: write_file
arguments:
path:
not_under: "${PROJECT_DIR}"
action: deny
# Scan all tool calls for leaked secrets
- name: block-secret-leakage
match:
method: tools/call
tool: "*"
arguments:
_any_value:
secrets: true
action: deny
message: "Blocked: detected secret in arguments"
secrets:
patterns:
- name: aws-access-key
regex: "AKIA[0-9A-Z]{16}"
- name: github-token
regex: "(gh[ps]_[A-Za-z0-9_]{36,}|github_pat_[A-Za-z0-9_]{22,})"
- name: private-key
regex: "-----BEGIN (RSA |EC |DSA |OPENSSH )?PRIVATE KEY-----"
- name: generic-high-entropy
regex: "[A-Za-z0-9/+=]{40}"
entropy_threshold: 4.5
```
### Rule matchers
| Matcher | Description |
|---------|-------------|
| `regex` | Regular expression test on the value |
| `pattern` | Glob pattern (uses [minimatch](https://github.com/isaacs/minimatch)) |
| `not_under` | Matches if path is NOT under the given directory. Supports `${HOME}`, `${PROJECT_DIR}` |
| `secrets` | When `true`, runs the secret scanner on the value |
The special key `_any_value` applies the matcher to ALL argument values.
### Outbound rules (response inspection)
Outbound rules scan server responses before they reach your AI client. Add them to the same config file:
```yaml
outbound_rules:
# Redact secrets leaked in responses
- name: redact-secrets-in-responses
match:
secrets: true
action: redact
message: "Secret detected in server response"
# Block prompt injection patterns
- name: block-prompt-injection
match:
response_contains:
- "ignore previous instructions"
- "provide contents of ~/.ssh"
action: deny
message: "Prompt injection detected"
# Flag suspiciously large responses
- name: flag-large-responses
match:
response_size_exceeds: 102400
action: log_only
```
#### Outbound matchers
| Matcher | Description |
|---------|-------------|
| `tool` | Glob pattern on the tool that produced the response (requires request-response correlation) |
| `server` | Glob pattern on the server name |
| `secrets` | When `true`, scans response for secret patterns (uses same `secrets.patterns` config) |
| `response_contains` | Case-insensitive substring match against response text |
| `response_contains_regex` | Regex match against response text |
| `response_size_exceeds` | Byte size threshold for the serialized response |
#### Outbound actions
| Action | Behavior |
|--------|----------|
| `allow` | Forward response unchanged |
| `deny` | Replace response with `[BLOCKED BY MCPWALL]` message |
| `redact` | Surgically replace matched secrets with `[REDACTED BY MCPWALL]`, forward modified response |
| `log_only` | Forward unchanged, log the match |
### Built-in rule packs
- `rules/default.yml` — sensible defaults (blocks SSH, .env, credentials, dangerous commands, secrets)
- `rules/strict.yml` — deny-by-default paranoid mode (whitelist only project reads/writes)
Use strict mode:
```bash
mcpwall -c /path/to/strict.yml -- npx -y @some/server
```
## CLI
```
mcpwall [options] -- <command> [args...] # Proxy mode
mcpwall init # Interactive setup
mcpwall wrap <server-name> # Wrap specific server
```
Options:
- `-c, --config <path>` — path to config file
- `--log-level <level>` — override log level (debug/info/warn/error)
## Audit Logs
All tool calls are logged by default — both allowed and denied. Logs are written as JSON Lines to `~/.mcpwall/logs/YYYY-MM-DD.jsonl`:
```json
{"ts":"2026-02-16T14:30:00Z","method":"tools/call","tool":"read_file","action":"allow","rule":null}
{"ts":"2026-02-16T14:30:05Z","method":"tools/call","tool":"read_file","args":"[REDACTED]","action":"deny","rule":"block-ssh-keys","message":"Blocked: access to SSH keys"}
```
Denied entries have args redacted to prevent secrets from leaking into logs.
mcpwall also prints color-coded output to stderr so you can see decisions in real time.
## Security Design
- **Bidirectional scanning**: Both inbound requests and outbound responses are evaluated against rules
- **Fail closed on invalid config**: Bad regex in a rule crashes at startup, never silently passes traffic
- **Fail open on outbound errors**: If response parsing fails, the raw response is forwarded (never blocks legitimate traffic)
- **Args redacted on deny**: Blocked tool call arguments are never written to logs
- **Surgical redaction**: Secrets in responses are replaced in-place, preserving the JSON-RPC response structure
- **Path traversal defense**: `not_under` matcher uses `path.resolve()` to prevent `../` bypass
- **Pre-compiled regexes**: All patterns compiled once at startup for consistent performance
- **No network**: Zero cloud calls, zero telemetry, runs entirely local
- **Deterministic**: Same input + same rules = same output, every time
## License
[Apache-2.0](./LICENSE)
---
mcpwall is not affiliated with or endorsed by Anthropic or the Model Context Protocol project. MCP is an open protocol maintained by the Agentic AI Foundation under the Linux Foundation.
