mcp-server-malcolm

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The first MCP server for Malcolm, the open-source network traffic analysis platform (Zeek + Suricata + Arkime + OpenSearch, with optional NetBox).

It gives any MCP-compatible AI agent structured access to Malcolm: search and aggregate network traffic, discover field names, query Suricata alerts, browse Arkime sessions, resolve NetBox assets, and check system health. Turn on the write classes and it can also create alerts, tag sessions, launch hunts, and upload PCAP.

Read-only until you opt in

With no configuration, this server exposes read tools only. It behaves like a read-only client, and nothing it does can change data in Malcolm.

The server splits write access into five classes, each behind its own environment flag and each off by default. It doesn't register a disabled class, so that class's tools never appear in list_tools() and can't be called. At startup it prints which classes are on:

[mcp-server-malcolm] write classes: alerting=off arkime-tag=off hunt-job=off pcap-upload=off arkime-view=off

Every write is additive. Version 1 has no tool that deletes data, removes a tag, or touches user accounts. It leaves those out on purpose (see Non-goals).

Why an MCP layer

Malcolm keeps all network metadata in one OpenSearch index (arkime_sessions3-*) with non-standard field names and its own filter syntax. An LLM asked to write raw OpenSearch DSL against that index gets it wrong more often than not. This server takes that job off the model:

• It exposes Malcolm's filter syntax instead of raw DSL.
• It provides field discovery so the model checks field names before it queries.
• It provides value enumeration so the model sees what values a field actually holds.
• It covers both field vocabularies. Arkime expressions take Arkime's own names (ip.src), the rest of Malcolm takes ECS names (source.ip), and Malcolm's own field list carries only the second set. arkime_field_search supplies the first.
• It wraps Suricata alert queries and handles the field mapping (suricata.alert.* vs rule.*).
• It adds NetBox asset context (IP-to-device, network segments).

The failure mode this is built against is a quiet one. Malcolm answers a query against a field it does not index with an empty result rather than an error, so a model that guesses a plausible-but-wrong name reads "no such traffic" and moves on. When a search comes back empty, this server checks the fields the query named and reports the name Malcolm actually stores the value under. That lookup runs only after a result set is already empty, so nothing is added to the model's context on queries that worked.

The write side follows the same idea. Rather than hand an agent the raw OpenSearch and NetBox passthroughs that Malcolm already leaves open to any authenticated user, this server exposes a small, named, audited set of write actions. More on that under Security model.

Read tools

These are always registered.

DSL core (backend-agnostic)

Plain OpenSearch DSL against the configured endpoint (Malcolm's /mapi/opensearch proxy). No Malcolm-specific query shape: point the base URL at any OpenSearch-compatible backend and they still work.

Core query

Field discovery (anti-hallucination)

These three malcolm_* tools cover the ECS names used by malcolm_search, malcolm_aggregate and the DSL tools. Anything going into an expression argument needs arkime_field_search instead: Arkime's parser accepts ip.src and rejects source.ip, and Malcolm's /mapi/fields does not list the expression names at all.

System health

Asset context (NetBox)

Arkime

Correlation and export

Write tools (opt-in)

Each class is enabled by setting its flag to true. Nothing here runs unless you ask for it.

• alerting: malcolm_create_alert indexes an analyst- or agent-generated finding as an alert document you can see in Malcolm's dashboards. It uses /mapi/event, Malcolm's own purpose-built write endpoint, which is the template the other classes follow.
• arkime-tag: arkime_add_tags adds tags to sessions. It only adds; tag removal needs a higher Arkime role and its own safety design, so it's deferred.
• hunt-job: arkime_create_hunt launches a cross-PCAP packet search (expensive, so scope the query first). arkime_hunt_status reads job progress and ships with the class.
• pcap-upload: malcolm_upload_pcap sends a local capture file to Malcolm for ingestion, with a client-side size cap. The file must live inside MALCOLM_MCP_UPLOAD_DIR; if that staging directory is unset, uploads are refused, so the tool can never be steered into reading an arbitrary file off the host.
• arkime-view: arkime_create_view saves a named search expression and arkime_create_shortcut saves a named value list (IOC set) referenced in expressions as $name. Both are additive — they let an agent persist hunting knowledge for the human team, and neither deletes or overwrites.

Every write tool carries the MCP annotations readOnlyHint: false and destructiveHint: false, so an MCP client can apply its own confirmation step before the call runs.

Security model

Malcolm's default deployment already gives any authenticated user unrestricted write access to raw OpenSearch (/mapi/opensearch/*) and full NetBox CRUD (/mapi/netbox/*). Both are bare reverse-proxies with no HTTP-verb filtering; Malcolm's own read-only mode removes them rather than trying to filter them. In the common auth modes, "logged in" means admin-equivalent.

Turning on a write class here does not open a door that was otherwise shut. That door is already open at the platform level. This server adds a curated way through it:

• A small, named set of write actions instead of a raw passthrough.
• Off by default, enabled one class at a time.
• An audit line for every write attempt.
• MCP annotations so the client can require confirmation.

This server does not expose the raw OpenSearch and NetBox write passthroughs, behind a flag or otherwise. Curating that surface is what it is for.

Audit

Every write attempt emits one line of JSON, on success and on failure:

{"ts": "2026-07-06T09:12:44Z", "tool": "arkime_add_tags", "class": "arkime-tag", "target": "ids=240601-abc", "params": {"tags": "suspicious"}, "outcome": "ok"}

outcome is one of ok, http_4xx, http_5xx, or error:<type>. Long parameter values are truncated, and PCAP bytes are never logged. The sink is stderr by default; set MALCOLM_MCP_AUDIT_FILE to append to a file instead. Read tools are not audited.

Quick start

You don't write any code to use this. An MCP client (Claude Code, Claude Desktop, Cursor, …) launches the server as a subprocess and talks to it over stdio; your job is to tell the client how to launch it and which credentials to inject.

1. Install

pip install mcp-server-malcolm

Or from source:

git clone https://github.com/nagameTW/mcp-server-malcolm.git
cd mcp-server-malcolm
pip install -e .

2. Register it with your client

Claude Code — one command, no config file to find:

claude mcp add malcolm \
  -e MALCOLM_URL=https://malcolm.example \
  -e MALCOLM_USERNAME=analyst \
  -e MALCOLM_PASSWORD='your-password' \
  -e MALCOLM_SSL_VERIFY=/path/to/malcolm-ca.crt \
  -- mcp-server-malcolm

Everything after -- is the launch command; each -e is an environment variable injected into it. Pick where the entry is stored with -s:

Confirm it came up with claude mcp list, which health-checks each server, and claude mcp get malcolm for the details.

For a project-scope entry, keep the secret in each person's shell rather than in the file:

{
  "mcpServers": {
    "malcolm": {
      "command": "mcp-server-malcolm",
      "env": { "MALCOLM_PASSWORD": "${MALCOLM_PASSWORD}" }
    }
  }
}

Other MCP clients — no equivalent CLI, so edit the client's own JSON config. The block is the same shape:

{
  "mcpServers": {
    "malcolm": {
      "command": "mcp-server-malcolm",
      "env": {
        "MALCOLM_URL": "https://malcolm.example",
        "MALCOLM_USERNAME": "analyst",
        "MALCOLM_PASSWORD": "your-password",
        "MALCOLM_SSL_VERIFY": "/path/to/malcolm-ca.crt"
      }
    }
  }
}

Claude Desktop reads claude_desktop_config.json; other clients vary — check their docs for the path.

If mcp-server-malcolm isn't on the PATH your client sees (common with a virtualenv), give the absolute path to the executable instead: /path/to/.venv/bin/mcp-server-malcolm.

3. Connection settings

On TLS: verification is on by default, and Malcolm ships self-signed certs. Pointing MALCOLM_SSL_VERIFY at Malcolm's CA bundle only works if Malcolm's server certificate carries a subjectAltName matching the hostname you connect to — the certificate generated by Malcolm's own setup has no SAN extension, so verification fails against it even with the right CA. For a remote Malcolm, install a certificate with a correct SAN. MALCOLM_SSL_VERIFY="false" disables verification entirely and is only acceptable against an isolated localhost lab; over a network it would send credentials and query results down an unauthenticated channel.

4. Enabling write tools (optional)

All five write classes are off unless you set their flag, so the default install is read-only. Add the flags to the same -e / env block:

-e MALCOLM_MCP_ENABLE_ALERTING=true
-e MALCOLM_MCP_AUDIT_FILE=/var/log/malcolm-mcp-audit.jsonl

The full flag list is in Configuration.

Running it by hand

Only useful for troubleshooting. A stdio MCP server has no interactive interface: started from a terminal it sits silently waiting for JSON-RPC on stdin, which is what a working server looks like. It does print the enabled write classes to stderr on startup, so this confirms the flags took effect:

mcp-server-malcolm          # or: python -m mcp_server_malcolm

Usage

Python (direct import)

Use MalcolmClient without the MCP layer:

import asyncio
from mcp_server_malcolm import MalcolmClient

async def main():
    client = MalcolmClient(
        base_url="https://malcolm.example",
        username="admin",
        password="admin",
    )

    # Search network traffic
    results = await client.search(
        filters={"event.dataset": "conn", "source.ip": "192.0.2.77"},
        limit=10,
    )

    # Aggregate by protocol
    agg = await client.aggregate(
        fields="network.protocol",
        filters={"network.direction": ["inbound", "outbound"]},
    )

    # Discover field names
    fields = await client.search_fields(keyword="useragent")

    # Get distinct values
    datasets = await client.field_values(field="event.dataset")

    # Look up a NetBox asset
    asset = await client.netbox_get(
        "api/ipam/ip-addresses/",
        params={"address": "192.0.2.77"},
    )

    await client.close()

asyncio.run(main())

Write primitives live behind the _write_* methods. Only the gated write tools reach them, not the direct-import path.

Malcolm filter syntax

Malcolm uses a simple JSON filter syntax, not OpenSearch DSL:

# Exact match
{"event.dataset": "conn"}

# Multiple values (OR)
{"network.direction": ["inbound", "outbound"]}

# Negation
{"!network.transport": "icmp"}

# Field must exist (not null)
{"!related.password": null}

# Combined (AND)
{"event.dataset": "dns", "source.ip": "192.0.2.77"}

Values match exactly. Malcolm compiles this dict to an OpenSearch terms query, so there is no wildcard: {"rule.name": "*MALWARE*"} looks for a signature literally named *MALWARE* and quietly finds nothing. For substring matching either enumerate the values first with malcolm_field_values and pass the ones you want as a list, or use search_dsl and write the wildcard query yourself. malcolm_alerts does that enumeration for you on its signature and category arguments.

Examples

Search DNS queries to a suspicious domain

malcolm_search(
  filters='{"event.dataset": "dns", "zeek.dns.query": "ntp.ubuntu.com"}',
  limit=20,
  time_from="7 days ago"
)

Aggregate top talkers by protocol

malcolm_aggregate(
  fields="source.ip,destination.ip,network.protocol",
  filters='{"network.direction": ["inbound", "outbound"]}',
  limit=20
)

Verify field names before querying

malcolm_field_search(prefix="zeek.dns")
malcolm_field_values(field="event.dataset")
malcolm_field_profile(field="zeek.ssl.server_name")

# Before writing an Arkime expression, look the name up in Arkime's own
# vocabulary. This returns "ip.src | srcIp | ip | general": the first name
# goes in an expression, the second wherever a tool asks for a db field.
arkime_field_search(keyword="src")

Create an alert (alerting class enabled)

malcolm_create_alert(
  title="Periodic beacon to 192.0.2.77",
  severity=2,
  description="60s-interval C2 candidate",
  source_ip="192.0.2.10",
  dest_ip="192.0.2.77"
)

Tag sessions for review (arkime-tag class enabled)

arkime_add_tags(session_ids="240601-abc,240601-def", tags="review,beacon")

Launch a hunt (hunt-job class enabled)

arkime_create_hunt(
  name="beacon-bytes",
  search="deadbeef",
  search_type="hex",
  total_sessions=42,
  start_time=1717200000,
  stop_time=1717203600,
  expression="ip==192.0.2.77"
)

Configuration reference

Malcolm API endpoints used

These endpoint paths and body shapes match Malcolm 26.06.1 and Arkime v6.5.0. Both drift between releases, so re-check against your own version if a write tool returns an unexpected error.

Non-goals

Version 1 leaves these out on purpose:

• Destructive writes (Arkime session delete, tag removal, user management).
• Raw OpenSearch write or raw NetBox CRUD passthrough, behind a flag or otherwise.
• The streamable-http transport (stdio only).

Requirements

• Python 3.11+
• A Malcolm instance with API access
• Network connectivity to Malcolm (HTTPS)

License

MIT © nagameTW