---

labels:

- 'Stage-Alpha'

summary: 'A rule-based stanza filtering module'

...

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**Note:** mod\_firewall is in its very early stages. This documentation

is liable to change, and some described functionality may be missing,

incomplete or contain bugs.

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Introduction

============

A firewall is an invaluable tool in the sysadmin's toolbox. However

while low-level firewalls such as iptables and pf are incredibly good at

what they do, they are generally not able to handle application-layer

rules.

The goal of mod\_firewall is to provide similar services at the XMPP

layer. Based on rule scripts it can efficiently block, bounce, drop,

forward, copy, redirect stanzas and more! Furthermore all rules can be

applied and updated dynamically at runtime without restarting the

server.

Details

=======

mod\_firewall loads one or more scripts, and compiles these to Lua code

that reacts to stanzas flowing through Prosody. The firewall script

syntax is unusual, but straightforward.

A firewall script is dominated by rules. Each rule has two parts:

conditions, and actions. When a stanza matches all of the conditions,

all of the actions are executed in order.

Here is a simple example to block stanzas from spammer@example.com:

    FROM: spammer@example.com

    DROP.

FROM is a condition, and DROP is an action. This is about as simple as

it gets. How about heading to the other extreme? Let's demonstrate

something more complex that mod\_firewall can do for you:

    %ZONE myorganisation: staff.myorg.example, support.myorg.example

    ENTERING: myorganisation

    KIND: message

    TIME: 12am-9am, 5pm-12am, Saturday, Sunday

    REPLY=Sorry, I am afraid our office is closed at the moment. If you need assistance, please call our 24-hour support line on 123-456-789.

This rule will reply with a short message whenever someone tries to send

a message to someone at any of the hosts defined in the 'myorganisation'

outside of office hours.

Specifying rule sets

--------------------

Firewall rules should be written into text files, e.g. `ruleset.pfw` file.

One or more rule files can be specified in the configuration using:

    firewall_scripts = { "path/to/ruleset.pfw", "path/to/ruleset2.pfw" }

If multiple files are specified and they both add rules to the same chains,

each file's rules will be processed in order, but the order of files is undefined.

Conditions

----------

All conditions must come before any action in a rule block. The

condition name is followed by a colon (':'), and the value to test for.

A condition can be preceded or followed by `NOT` to negate its match.

For example:

    NOT FROM: user@example.com

    KIND NOT: message

Some conditions do not take parameters, and these should end with just a

question mark, like:

    IN ROSTER?

### Zones

A 'zone' is one or more hosts or JIDs. It is possible to match when a

stanza is entering or leaving a zone, while at the same time not

matching traffic passing between JIDs in the same zone.

Zones are defined at the top of a script with the following syntax (they

are not part of a rule block):

    %ZONE myzone: host1, host2, user@host3, foo.bar.example

There is an automatic zone named `$local`, which automatically includes

all of the current server's active hosts (including components). It can

be used to match stanzas entering or leaving the current server.

A host listed in a zone also matches all users on that host (but not

subdomains).

The following zone-matching conditions are supported:

  Condition    Matches

  ------------ ------------------------------------------

  `ENTERING`   When a stanza is entering the named zone

  `LEAVING`    When a stanza is leaving the named zone

### Lists

It is possible to create or load lists of strings for use in scripts. For example, you might load a JID blacklist,

a list of malware URLs or simple words that you want to filter messages on.

  List type    Example

  -----------  -----------------------

  memory       %LIST spammers: memory

  file         %LIST spammers: file:/etc/spammers.txt

  http         %LIST spammers: http://example.com/spammers.txt

#### CHECK LIST

Checks whether a simple expression is found in a given list.

Example:

    %LIST blacklist: file:/etc/prosody/blacklist.txt

    # Rule to block presence subscription requests from blacklisted JIDs

    KIND: presence

    TYPE: subscribe

    CHECK LIST: blacklist contains $<@from>

    BOUNCE=policy-violation (Your JID is blacklisted)

#### SCAN

SCAN allows you to search inside a stanza for a given pattern, and check each result against a list. For example,

you could scan a message body for words and check if any of the words are found in a given list.

Before using SCAN, you need to define a search location and a pattern. The search location uses the same 'path'

format as documented under the 'INSPECT' condition. Patterns can be any valid Lua pattern.

To use the above example:

    # Define a search location called 'body' which fetches the text of the 'body' element

    %SEARCH body: body#

    # Define a pattern called 'word' which matches any sequence of letters

    %PATTERN word: [A-Za-z]+

    # Finally, we also need our list of "bad" words:

    %LIST badwords: file:/etc/prosody/bad_words.txt

    # Now we can use these to SCAN incoming stanzas

    # If it finds a match, bounce the stanza

    SCAN: body for word in badwords

    BOUNCE=policy-violation (This word is not allowed!)

#### COUNT

COUNT is similar to SCAN, in that it uses a defined SEARCH and breaks it up according to a PATTERN. Then it

counts the number of results.

For example, to block every message with more than one URL:

    # Define a search location called 'body' which fetches the text of the 'body' element

    %SEARCH body: body#

    # Define a pattern called 'url' which matches HTTP links

    %PATTERN url: https?://%S+

    COUNT: url in body > 1

    BOUNCE=policy-violation (Up to one HTTP URL is allowed in messages)

### Stanza matching

  Condition   Matches

  ----------- ------------------------------------------------------------------------------------------------------------------------------------------------------------

  `KIND`      The kind of stanza. May be 'message', 'presence' or 'iq'

  `TYPE`      The type of stanza. This varies depending on the kind of stanza. See 'Stanza types' below for more information.

  `PAYLOAD`   The stanza contains a child with the given namespace. Useful for determining the type of an iq request, or whether a message contains a certain extension.

  `INSPECT`   The node at the specified path exists or matches a given string. This allows you to look anywhere inside a stanza. See below for examples and more.

#### Stanza types

  Stanza     Valid types

  ---------- ------------------------------------------------------------------------------------------

  iq         get, set, result, error

  presence   *available*, unavailable, probe, subscribe, subscribed, unsubscribe, unsubscribed, error

  message    normal, chat, groupchat, headline, error

**Note:** The type 'available' for presence does not actually appear in

the protocol. Available presence is signalled by the omission of a type.

Similarly, a message stanza with no type is equivalent to one of type

'normal'. mod\_firewall handles these cases for you automatically.

### Sender/recipient matching

  Condition     Matches

  ------------- -------------------------------------------------------

  `FROM`        The JID in the 'from' attribute matches the given JID.

  `TO`          The JID in the 'to' attribute matches the given JID.

  `TO SELF`     The stanza is sent by any of a user's resources to their own bare JID.

  `TO FULL JID` The stanza is addressed to a valid full JID on the local server (full JIDs include a resource at the end, and only exist for the lifetime of a single session, therefore the recipient must be online, or this check will not match).

The TO and FROM conditions both accept wildcards in the JID when the wildcard

expression is enclosed in angle brackets ('\<...\>'). For example:

    # All users at example.com

    FROM: <*>@example.com

    # The user 'admin' on any subdomain of example.com

    FROM: admin@<*.example.com>

You can also use [Lua's pattern

matching](http://www.lua.org/manual/5.1/manual.html#5.4.1) for more

powerful matching abilities. Patterns are a lightweight

regular-expression alternative. Simply contain the pattern in double

angle brackets. The pattern is automatically anchored at the start and

end (so it must match the entire portion of the JID).

    # Match admin@example.com, and admin1@example.com, etc.

    FROM: <<admin%d*>>@example.com

**Note:** It is important to know that 'example.com' is a valid JID on

its own, and does **not** match 'user@example.com'. To perform domain

whitelists or blacklists, use Zones.

  Condition        Matches

  ---------------- ---------------------------------------------------------------

  `FROM_EXACTLY`   The JID in the 'from' attribute exactly matches the given JID

  `TO_EXACTLY`     The JID in the 'to' attribute exactly matches the given JID

These additional conditions do not support pattern matching, but are

useful to match the exact to/from address on a stanza. For example, if

no resource is specified then only bare JIDs will be matched. TO and FROM

match all resources if no resource is specified to match.

**Note:** Some chains execute before Prosody has performed any

normalisation or validity checks on the to/from JIDs on an incoming

stanza. It is not advisable to perform access control or similar rules

on JIDs in these chains (see the chain documentation for more info).

#### INSPECT

INSPECT takes a 'path' through the stanza to get a string (an attribute

value or text content). An example is the best way to explain. Let's

check that a user is not trying to register an account with the username

'admin'. This stanza comes from [XEP-0077: In-band

Registration](http://xmpp.org/extensions/xep-0077.html#example-4):

``` xml

<iq type='set' id='reg2'>

  <query xmlns='jabber:iq:register'>

    <username>bill</username>

    <password>Calliope</password>

    <email>bard@shakespeare.lit</email>

  </query>

</iq>

```

    KIND: iq

    TYPE: set

    PAYLOAD: jabber:iq:register

    INSPECT: {jabber:iq:register}query/username#=admin

    BOUNCE=not-allowed (The username 'admin' is reserved.)

That weird string deserves some explanation. It is a path, divided into

segments by '/'. Each segment describes an element by its name,

optionally prefixed by its namespace in curly braces ('{...}'). If the

path ends with a '\#' then the text content of the last element will be

returned. If the path ends with '@name' then the value of the attribute

'name' will be returned.

You can use INSPECT to test for the existence of an element or attribute,

or you can see if it is equal to a string by appending `=STRING` (as in the

example above). Finally, you can also test whether it matches a given Lua

pattern by using `~=PATTERN`.

INSPECT is somewhat slower than the other stanza matching conditions. To

minimise performance impact, always place it below other faster

condition checks where possible (e.g. above we first checked KIND, TYPE

and PAYLOAD matched before INSPECT).

### Roster

These functions access the roster of the recipient (only). Therefore they cannot (currently)

be used in some chains, such as for outgoing messages (the recipient may be on another server).

Performance note: this check can potentially cause storage access (especially if the recipient

is currently offline), so you may want to limit its use in high-traffic situations, and place

it below other checks (such as a rate limiter).

#### IN ROSTER

Tests whether the sender is in the recipient's roster.

    IN ROSTER?

#### IN ROSTER GROUP

Tests whether the sender is in the recipient's roster, and in the named group.

    IN ROSTER GROUP: Friends

#### SUBSCRIBED

Tests whether the recipient is subscribed to the sender, ie will receive

presence updates from them.

Note that this *does* work, regardless of direction and which chain is

used, since both the sender and the recipient will have mirrored roster

entries.

### Groups

Using Prosody's mod\_groups it is possible to define groups of users on the server. You can

match based on these groups in firewall rules.

  Condition         Matches

  ----------------- ----------------------------

  `FROM GROUP`      When the stanza is being sent from a member of the named group

  `TO GROUP`        When the stanza is being sent to a member of the named group

  `CROSSING GROUPS` When the stanza is being sent between users of different named groups

#### CROSSING GROUPS

The `CROSSING GROUPS` condition takes a comma-separated list of groups to check. If the

sender and recipient are not in the same group (only the listed groups are checked), then the

this condition matches and the stanza is deemed to be crossing between groups.

For example, if you had three groups: Engineering, Marketing and Employees. All users are

members of the 'Employees' group, and the others are for employees of the named department only.

To prevent employees in the marketing department from communicating with engineers, you could use

the following rule:

```

CROSSING GROUPS: Marketing, Engineering

BOUNCE=policy-violation (no communication between these groups is allowed!)

```

This works, even though both the users are in the 'Employees' group, because that group is not listed

in the condition.

In the above example, a user who is member of both groups is not restricted.

#### SENT DIRECTED PRESENCE TO SENDER

This condition matches if the recipient of a stanza has previously sent directed presence to the sender of the stanza. This

is often done in XMPP to exchange presence information with JIDs that are not on your roster, such as MUC rooms.

This condition does not take a parameter - end the condition name with a question mark:

    # Rule to bounce messages from senders not in the roster who haven't been sent directed presence

    NOT IN ROSTER?

    NOT SENT DIRECTED PRESENCE TO SENDER?

    BOUNCE=service-unavailable

### Admins

Prosody allows certain JIDs to be declared as administrators of a host, component or the whole server.

  Condition        Matches

  ---------------- -------------------------------------------------------------------------------------

  `TO ADMIN`       When the recipient of the stanza is admin of the current host

  `FROM ADMIN`     When the sender of the stanza is admin of the current host

  `FROM ADMIN OF`  When the sender of the stanza is an admin of the named host on the current server

  `TO ADMIN OF`    When the recipient of the stanza is an admin of the named host on the current server

### Time and date

#### TIME

Matches stanzas sent during certain time periods.

  Condition   Matches

  ----------- -------------------------------------------------------------------------------------------

  TIME        When the current server local time is within one of the comma-separated time ranges given

    TIME: 10pm-6am, 14:00-15:00

    REPLY=Zzzz.

#### DAY

It is also possible to match only on certain days of the week.

  Condition   Matches

  ----------- -----------------------------------------------------------------------------------------------------

  DAY         When the current day matches one, or falls within a rage, in the given comma-separated list of days

Example:

    DAY: Sat-Sun, Wednesday

    REPLY=Sorry, I'm out enjoying life!

All times and dates are handled in the server's local time.

### Rate-limiting

It is possible to selectively rate-limit stanzas, and use rules to

decide what to do with stanzas when over the limit.

First, you must define any rate limits that you are going to use in your

script. Here we create a limiter called 'normal' that will allow 2

stanzas per second, and then we define a rule to bounce messages when

over this limit. Note that the `RATE` definition is not part of a rule

(multiple rules can share the same limiter).

    %RATE normal: 2 (burst 3)

    KIND: message

    LIMIT: normal

    BOUNCE=policy-violation (Sending too fast!)

The 'burst' parameter on the rate limit allows you to spread the limit

check over a given time period. For example the definition shown above

will allow the limit to be temporarily surpassed, as long as it is

within the limit after 3 seconds. You will almost always want to specify

a burst factor.

Both the rate and the burst can be fractional values. For example a rate

of 0.1 means only one event is allowed every 10 seconds.

The LIMIT condition actually does two things; first it counts against

the given limiter, and then it checks to see if the limiter over its

limit yet. If it is, the condition matches, otherwise it will not.

  Condition   Matches

  ----------- --------------------------------------------------------------------------------------------------

  `LIMIT`     When the named limit is 'used up'. Using this condition automatically counts against that limit.

**Note:** Reloading mod\_firewall resets the current state of any

limiters.

#### Dynamic limits

Sometimes you may want to have multiple throttles in a single condition, using some property of the session or stanza

to determine which throttle to use. For example, you might have a limit for incoming stanzas, but you want to limit by

sending JID, instead of all incoming stanzas sharing the same limit.

You can use the 'on' keyword for this, like so:

    LIMIT: normal on EXPRESSION

For more information on expressions, see the section later in this document.

Each value of 'EXPRESSION' has to be tracked individually in a table, which uses a small amount of memory. To prevent

memory exhaustion, the number of tracked values is limited to 1000 by default. You can override this by setting the

maximum number of table entries when you define the rate:

    %RATE normal: 2 (burst 3) (entries 4096)

Old values are automatically removed from the tracking table. However if the tracking table becomes full, new entries

will be rejected - it will behave as if the rate limit was reached, even for values that have not been seen before. Since

this opens up a potential denial of service (innocent users may be affected if malicious users can fill up the tracking

table within the limit period). You can choose to instead "fail open", and allow the rate limit to be temporarily bypassed

when the table is full. To choose this behaviour, add `(allow overflow)` to the RATE definition.

### Session marking

It is possible to 'mark' sessions (see the MARK_ORIGIN action below). To match stanzas from marked sessions, use the

`ORIGIN_MARKED` condition.

  Condition                       Description

  ------------------------------- ---------------------------------------------------------------

  ORIGIN MARKED: markname         Matches if the origin has been marked with 'markname'.

  ORIGIN MARKED: markname (Xs)    Matches if the origin has been marked with 'markname' within the past X seconds.

Example usage:

    # This rule drops messages from sessions that have been marked as spammers in the past hour

    ORIGIN MARKED: spammer (3600s)

    DROP.

    # This rule marks the origin session as a spammer if they send a message to a honeypot JID

    KIND: message

    TO: honeypot@example.com

    MARK ORIGIN=spammer

Actions

-------