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Mozilla InvestiGator Concepts & Internal Components

MIG is a platform to perform investigative surgery on remote endpoints. It enables investigators to obtain information from large numbers of systems in parallel, thus accelerating investigation of incidents.

Besides scalability, MIG is designed to provide strong security primitives:

  • Access control is ensured by requiring GPG signatures on all actions. Sensitive actions can also request signatures from multiple investigators. An attacker who takes over the central server will be able to read non-sensitive data, but will not be able to send actions to agents. The GPG keys are securely kept by their investigators.
  • Privacy is respected by never retrieving raw data from endpoints. When MIG is run on laptops or phones, end-users can request reports on the operations performed on their devices. The 2-man-rule for sensitive actions also prevents rogue investigators invading privacy.
  • Reliability is built in. No component is critical. If an agent crashes, it will attempt to recover and reconnect to the platform indefinitely. If the platform crashes, a new platform can be rebuilt rapidly without backups.

MIG privileges a model where requesting information from endpoints is fast and simple. It does not attempt to record everything all the time. Instead, it assumes that when a piece of information is needed, it will be easy to retrieve it.

It's an army of Sherlock Holmes, ready to interrogate your network within milliseconds.


  • Investigators: humans who use clients to investigate things on agents
  • Agent: a small program that runs on a remote endpoint. It receives commands from the scheduler through the relays, executes those commands using modules, and sends the results back to the relays.
  • Loader: a small bootstrapping program that can optionally be used to keep agents up to date on remote endpoints
  • Module: single feature Go program that does stuff, like inspecting a file system, listing connected IP addresses, creating user accounts or adding firewall rules
  • Scheduler: a messaging daemon that routes actions and commands to and from agents.
  • Relay: a RabbitMQ server that queues messages between schedulers and agents.
  • Database: a storage backend used by the scheduler and the api
  • API: a REST api that exposes the MIG platform to clients
  • Client: a program used by an investigator to interface with MIG (like the MIG Console, or the action generator)
  • Worker: a worker is a small extension to the scheduler and api that performs very specific tasks based on events received via the relay.

An investigator uses a client (such as the MIG Console) to communicate with the API. The API interfaces with the Database and the Scheduler. When an action is created by an investigator, the API receives it and writes it into the spool of the scheduler (they share it via NFS). The scheduler picks it up, creates one command per target agent, and sends those commands to the relays (running RabbitMQ). Each agent is listening on its own queue on the relay. The agents execute their commands, and return the results through the same relays (same exchange, different queues). The scheduler writes the results into the database, where the investigator can access them through the API. The agents also use the relays to send heartbeat at regular intervals, such that the scheduler always knows how many agents are alive at a given time.

The end-to-end workflow is:

{investigator} -https-> {API}        {Scheduler} -amqps-> {Relays} -amqps-> {Agents}
                            \           /
                          sql\         /sql

Below is a high-level view of the architecture:


1   Actions

Actions are JSON files created by investigators to perform tasks on agents.

For example, an investigator who wants to verify that root passwords are hashed and salted on linux systems, would use the following action:

        "name": "verify root password storage method",
        "target": "agents.queueloc like 'linux.%'",
        "threat": {
                "family": "compliance",
                "level": "low",
                "ref": "syslowauth3",
                "type": "system"
        "description": {
                "author": "Julien Vehent",
                "email": "",
                "revision": 201503121200
        "operations": [
                        "module": "file",
                        "parameters": {
                                "searches": {
                                        "root_passwd_hashed_or_disabled": {
                                                "paths": [
                                                "contents": [
        "syntaxversion": 2

The parameters are:

  • name: a string that represents the action.

  • target: a search string used by the scheduler to find agents to run the action on. The target format uses Postgresql's WHERE condition format against the agents table of the database. This method allows for complex target queries, like running an action against a specific operating system, or against an endpoint that has a given public IP, etc...

    The most simple query that targets all agents is name like '%' (the % character is a wildcard in SQL pattern matching). Targeting by OS family can be done on the os parameters such as os='linux' or os='darwin'.

    Combining conditions is also trivial: version='' and heartbeattime > NOW() - interval '1 minute' will only target agents that run a specific version and have sent a heartbeat during the last minute.

    Complex queries are also possible. For example: imagine an action with ID 1 launched against 10,000 endpoints, which returned 300 endpoints with positive results. We want to launch action 2 on those 300 endpoints only. It can be accomplished with the following target condition. (note: you can reuse this condition by simply changing the value of actionid)

id IN (select agentid from commands, json_array_elements(commands.results) as r where actionid=1 and r#>>'{foundanything}' = 'true')
  • description and threat: additional fields to describe the action
  • operations: an array of operations, each operation calls a module with a set of parameters. The parameters syntax are specific to the module.
  • syntaxversion: indicator of the action format used. Should be set to 2

Upon generation, additional fields are appended to the action:

  • pgpsignatures: all of the parameters above are concatenated into a string and signed with the investigator's private GPG key. The signature is part of the action, and used by agents to verify that an action comes from a trusted investigator. PGPSignatures is an array that contains one or more signatures from authorized investigators.
  • validfrom and expireafter: two dates that constrain the validity of the action to a UTC time window.

The steps involved with issuing actions are:

  1. Generate the JSON document of the action
  2. create a string representation of the action in the format "name=%s;target=%s;validfrom=%d;expireafter=%s;operations=%s;", where:

For example, if you run the following mig command:

mig file -t "tags->>'operator'='opsec'" -path /etc -name passwd

The serialized operations string will be:


The order of the keys is very important here, because it must be exactly the same between the client that performs the signature and the agent that will reconstruct the string to verify the signature.

At the end of this, you should have a string representation of the action that looks like this:

name=my fancy action;target=tags->>'operator'='opsec';validfrom=1486736196;expireafter=%!s(int64=1486736556);operations=[{"module":"file","parameters":{"searches":{"s1":{"names":["meihm"],"options":{"macroal":false,"matchall":true,"matchlimit":1000,"maxdepth":1000,"maxerrors":30,"mismatch":null},"paths":["/etc/passwd"]}}}}];
  1. Take the string representation of the action and sign it with the PGP private key of the investigator. This is where you will need the PGP library or tool to perform the signature. PGP supports various signature types, so the type you want is an "ARMORED DETACHED SIGNATURE" to get the signature in a multiline wrapped format, like this:
Version: PGP client blah blah blah
Comment: random text

  1. Take the detached signature, remove the header, footer, version and comment, and store the rest as a one line string. Taking the example above, the signature would be:
  1. Store the signature string in the action JSON under the "pgpsignatures" array. Technically, MIG supports multiple signatures per action, which is useful to require multiple investigators to approve an action. We won't address this use case in the UI yet.
"pgpsignatures": [
  1. Publish the JSON of the action to the POST /api/v1/action/create/ endpoint.

2   Investigation workflow

The diagram below represents the full workflow from the launch of an action by an investigation, to the retrieval of results from the database. The steps are explained in the legend of the diagram, and map to various components of MIG.

Actions are submitted to the API by trusted investigators. PGPSignatures are verified by the API and each agent prior to running any command.

View full size diagram.

3   Access Control Lists

Not all keys can perform all actions. The scheduler, for example, sometimes needs to issue specific actions to agents but shouldn't be able to perform more dangerous actions. This is enforced by an Access Control List, or ACL, stored on the agents. An ACL describes who can access what function of which module. It can be used to require multiple signatures on specific actions, and limit the list of investigators allowed to perform an action.

An ACL is composed of permissions, which are JSON documents hardwired into the agent configuration. In the future, MIG will dynamically ship permissions to agents.

Below is an example of a permission for the filechecker module:

    "filechecker": {
        "minimumweight": 2,
        "investigators": {
            "Bob Kelso": {
                "fingerprint": "E60892BB9BD...",
                "weight": 2
            "John Smith": {
                "fingerprint": "9F759A1A0A3...",
                "weight": 1

investigators contains a list of users with their PGP fingerprints, and their weight, an integer that represents their access level. When an agent receives an action that calls the filechecker module, it will first verify the signatures of the action, and then validates that the signers are authorized to perform the action. This is done by summing up the weights of the signatures, and verifying that they equal or exceed the minimum required weight.

Thus, in the example above, investigator John Smith cannot issue a filechecker action alone. His weight of 1 doesn't satisfy the minimum weight of 2 required by the filechecker permission. Therefore, John will need to ask investigator Bob Kelso to sign his action as well. The weight of both investigators are then added, giving a total of 3, which satisfies the minimum weight of 2.

This method gives ample flexibility to require multiple signatures on modules, and ensures that one investigator cannot perform sensitive actions on remote endpoints without the permissions of others.

The default permission default can be used as a default for all modules. It has the following syntax:

        "default": {
                "minimumweight": 2,
                "investigators": { ... }

The default permission is overridden by module specific permissions.

The ACL is currently applied to modules. In the future, ACL will have finer control to authorize access to specific functions of modules. For example, an investigator could be authorized to call the regex function of filechecker module, but only in /etc. This functionality is not implemented yet.

4   Threat Model

Running an agent as root on a large number of endpoints means that Mozilla InvestiGator is a target of choice to compromise an infrastructure. Without proper protections, a vulnerability in the agent or in the platform could lead to a compromission of the endpoints.

The architectural choices made in MIG diminish the exposure of the endpoints to a compromise. And while the risk cannot be reduced to zero entirely, it would take an attacker direct control on the investigator's key material, or be root on the infrastructure in order to take control of MIG.

MIG's security controls include:

  • Strong GPG security model
  • Infrastructure resiliency
  • No port listening
  • Protection of connections to the relays
  • Randomization of the queue names
  • Whitelisting of agents
  • Limit data extraction to a minimum

4.1   Strong GPG security model

All actions that are passed to the MIG platform and to the agents require valid GPG signatures from one or more trusted investigators. The public keys of trusted investigators are hardcoded in the agents, making it almost impossible to override without root access to the endpoints, or access to an investigator's private key. The GPG private keys are never seen by the MIG platform (API, Scheduler, Database or Relays). A compromise of the platform would not lead to an attacker taking control of the agents and compromising the endpoints.

4.2   Infrastructure resiliency

One of the design goals of MIG is to make each components as stateless as possible. The database is used as a primary data store, and the schedulers and relays keep data in transit in their respective cache. But any of these components can go down and be rebuilt without compromising the resiliency of the platform. As a matter of fact, it is strongly recommended to rebuild each of the platform components from scratch on a regular basis, and only keep the database as a persistent storage.

Unlike other systems that require constant network connectivity between the agents and the platform, MIG is designed to work with intermittent or unreliable connectivity with the agents. The rabbitmq relays will cache commands that are not consumed immediately by offline agents. These agents can connect to the relay whenever they choose to, and pick up outstanding tasks.

If the relays go down for any period of time, the agents will attempt to reconnect at regular intervals continuously. It is trivial to rebuild a fresh rabbitmq cluster, even on a new IP space, as long as the FQDN of the cluster, and the TLS cert/key and credentials of the AMQPS access point remain the same.

4.3   No port listening

The agents do not accept incoming connections. There is no listening port that an attacker could use to exploit a vulnerability in the agent. Instead, the agent connects to the platform by establishing an outbound connection to the relays. The connection uses TLS, making it theorically impossible for an attacker to MITM without access to the PKI and DNS, both of which are not part of the MIG platform.

4.4   Protection of connections to the relays

The rabbitmq relay of a MIG infrastructure may very well be listening on the public internet. This is used when MIG agents are distributed into various environments, as opposed to concentrated on a single network location. RabbitMQ and Erlang provide a stable network stack, but are not shielded from a network attack that would take down the cluster. To reduce the exposure of the AMQP endpoints, the relays use AMQP over TLS and require the agents to present a client certificate before accepting the connection.

The client certificate is shared across all the agents. It is not used as an authentication mechanism. Its sole purpose is to limit the exposure of a public AMQP endpoint. Consider it a network filter.

Once the TLS connection between the agent and the relay is established, the agent will present a username and password to open the AMQP connection. Again, these credentials are shared across all agents, and are not used to authenticate individual agents. Their role is to assign an ACL to the agent. The ACL limits the AMQP action an agent can perform on the cluster. See rabbitmq configuration for more information.

4.5   Randomization of the queue names

The protections above limit the exposure of the AMQP endpoint, but since the secrets are shared across all agents, the possibility still exists that an attacker gains access to the secrets, and establishes a connection to the relays.

Such access would have very limited capabilities. It cannot be used to publish commands to the agents, because publication is ACL-limited to the scheduler. It can be used to publish fake results to the scheduler, or listen on the agent queue for incoming commands.

Both are made difficult by prepending a random number to the name of an agent queue. An agent queue is named using the following scheme:

mig.agt.<OS family>.<Hostname>.<uid>

The OS and hostname of a given agent are easy to guess, but the uid isn't. The UID is a 64 bits integer composed of nanosecond timestamps and a random 32 bits integer, chosen by the agent on first start. It is specific to an endpoint.

4.6   Whitelisting of agents

At the moment, MIG does not provide a strong mechanism to authenticate agents. It is a work in progress, but for now agents are whitelisted in the scheduler using the queuelocs that are advertised in the heartbeat messages. Spoofing the queueloc string is difficult, because it contains a random value that is specific to an endpoint. An attacker would need access to the random value in order to spoof an agent's identity. This method provides a basic access control mechanism. The long term goal is to allow the scheduler to call an external database to authorize agents. In AWS, the scheduler could call the AWS API to verify that a given agent does indeed exist in the infrastructure. In a traditional datacenter, this could be an inventory database.

4.7   Limit data extraction to a minimum

Agents are not meant to retrieve raw data from their endpoints. This is more of a good practice rather than a technical limitation. The modules shipped with the agent are meant to return boolean answers of the type "match" or "no match".

It could be argued that answering "match" on sensitive requests is similar to extracting data from the agents. MIG does not solve this issue.. It is the responsibility of the investigators to limit the scope of their queries (ie, do not search for a root password by sending an action with the password in the regex).

The goal here is to prevent a rogue investigator from dumping a large amount of data from an endpoint. MIG could trigger a memory dump of a process, but retrieving that data will require direct access to the endpoint.

Note that MIG's database keeps records of all actions, commands and results. If sensitive data were to be collected by MIG, that data would be available in the database.