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Daniel Thayer b02709f88f Fix broken links in the documentation 
Also removed a duplicate link under "Script Reference".
2013-09-11 16:32:02 -05:00

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This document summarizes the most important changes in the current Bro
release. For a complete list of changes, see the ``CHANGES`` file
(note that submodules, such as BroControl and Broccoli, come with
their own CHANGES.)
Bro 2.2 (Work In Progress)
==========================
New Functionality
-----------------
- GPRS Tunnelling Protocol (GTPv1) decapsulation.
- GridFTP support. TODO: Extend.
- Modbus support. TODO: Extend.
- DNP3 support. TODO: Extend.
- ssl.log now also records the subject client and issuer certificates.
- Hooks: TODO: Briefly summarize the documention from
doc/scripts/builtins.rst here.
- The ASCII writer can now output CSV files on a per filter basis.
- Bro's language now has a working "switch" statement that generally
behaves like C-style switches except case labels can be comprised of
multiple literal constants delimited by commas. Only atomic types
are allowed for now. Case label bodies that don't execute a
"return" or "break" statement will fall through to subsequent cases.
A default case label is allowed.
- Bro's language now has a new set of types "opaque of X". Opaque
values can be passed around like other values but they can only be
manipulated with BiF functions, not with other operators. Currently,
the following opaque types are supported:
- opaque of md5
- opaque of sha1
- opaque of sha256
- opaquey of entropy.
They go along with the corrsponding BiF functions md5_*, sha1_*,
sha256_*, and entropy_*, respectively. Note that these functions
have changed their signatures to work with opaques types rather
than global state as it was before.
- The scripting language now supports a constructing sets, tables,
vectors, and records by name::
type MyRecordType: record {
c: count;
s: string &optional;
};
global r: MyRecordType = record($c = 7);
type MySet: set[MyRec];
global s = MySet([$c=1], [$c=2]);
- Strings now support the subscript operator to extract individual
characters and substrings (e.g., s[4], s[1,5]). The index expression
can take up to two indices for the start and end index of the
substring to return (e.g. "mystring[1,3]").
- Functions now support default parameters, e.g.:
global foo: function(s: string, t: string &default="abc", u: count &default=0);
- Scripts can now use two new "magic constants" @DIR and @FILENAME
that expand to the directory path of the current script and just the
script file name without path, respectively. (Jon Siwek)
- The new file analysis framework moves most of the processing of file
content from script-land into the core, where it belongs. See
doc/file-analysis.rst for more information.
Much of this is an internal change, but the framework also comes
with the following user-visibible functionality (some of that was
already available before, but done differently):
[TODO: Update with changes from 984e9793db56.]
- A binary input reader interfaces the input framework with file
analysis, allowing to inject files on disk into Bro's
processing.
- Supports for analyzing data transfereed via HTTP range
requests.
- HTTP:
* Identify MIME type of message.
* Extract message to disk.
* Compute MD5 for messages.
- SMTP:
* Identify MIME type of message.
* Extract message to disk.
* Compute MD5 for messages.
* Provide access to start of entity data.
- FTP data transfers: Identify MIME type; record to disk.
- IRC DCC transfers: Record to disk.
- New packet filter framework supports BPF-based load-balancing,
shunting, and sampling; plus plugin support to customize filters
dynamically.
- Bro now provides Bloom filters of two kinds: basic Bloom filters
supporting membership tests, and counting Bloom filters that track
the frequency of elements. The corresponding functions are:
bloomfilter_basic_init(fp: double, capacity: count, name: string &default=""): opaque of bloomfilter
bloomfilter_basic_init2(k: count, cells: count, name: string &default=""): opaque of bloomfilter
bloomfilter_counting_init(k: count, cells: count, max: count, name: string &default=""): opaque of bloomfilter
bloomfilter_add(bf: opaque of bloomfilter, x: any)
bloomfilter_lookup(bf: opaque of bloomfilter, x: any): count
bloomfilter_merge(bf1: opaque of bloomfilter, bf2: opaque of bloomfilter): opaque of bloomfilter
bloomfilter_clear(bf: opaque of bloomfilter)
See <INSERT LINK> for full documentation.
- Bro now provides a probabilistic data structure for computing
"top k" elements. The corresponding functions are:
topk_init(size: count): opaque of topk
topk_add(handle: opaque of topk, value: any)
topk_get_top(handle: opaque of topk, k: count)
topk_count(handle: opaque of topk, value: any): count
topk_epsilon(handle: opaque of topk, value: any): count
topk_size(handle: opaque of topk): count
topk_sum(handle: opaque of topk): count
topk_merge(handle1: opaque of topk, handle2: opaque of topk)
topk_merge_prune(handle1: opaque of topk, handle2: opaque of topk)
See <INSERT LINK> for full documentation.
- base/utils/exec.bro provides a module to start external processes
asynchronously and retrieve their output on termination.
base/utils/dir.bro uses it to monitor a directory for changes, and
base/utils/active-http.bro for providing an interface for querying
remote web servers.
- Summary statistics framework. [Extend]
- A number of new applications build on top of the summary statistics
framework:
* Scan detection: Detectors for port and address scans return. See
policy/misc/scan.bro.
* Tracerouter detector: policy/misc/detect-traceroute
* Web application detection/measurement: policy/misc/app-metrics.bro
* FTP brute-forcing detector: policy/protocols/ftp/detect-bruteforcing.bro
* HTTP-based SQL injection detector: policy/protocols/http/detect-sqli.bro
(existed before, but now ported to the new framework)
* SSH brute-forcing detector feeding the intelligence framework:
policy/protocols/ssh/detect-bruteforcing.bro
Changed Functionality
---------------------
- We removed the following, already deprecated, functionality:
* Scripting language:
- &disable_print_hook attribute.
* BiF functions:
- parse_dotted_addr(), dump_config(),
make_connection_persistent(), generate_idmef(),
split_complete()
- md5_*, sha1_*, sha256_*, and entropy_* have all changed
their signatures to work with opaque types (see above).
- Removed a now unused argument from "do_split" helper function.
- "this" is no longer a reserved keyword.
- The Input Framework's update_finished event has been renamed to
end_of_data. It will now not only fire after table-reads have been
completed, but also after the last event of a whole-file-read (or
whole-db-read, etc.).
- Renamed the option defining the frequency of alarm summary mails to
'Logging::default_alarm_mail_interval'. When using BroControl, the
value can now be set with the new broctl.cfg option
"MailAlarmsInterval".
- We have completely reworded the "notice_policy" mechanism. It now no
linger uses a record of policy items but a "hook", a new language
element that's roughly equivalent to a function with multiple
bodies. The documentation [TODO: insert link] describes how to use
the new notice policy. For existing code, the two main changes are:
- What used to be a "redef" of "Notice::policy" now becomes a hook
implementation. Example:
Old::
redef Notice::policy += {
[$pred(n: Notice::Info) = {
return n$note == SSH::Login && n$id$resp_h == 10.0.0.1;
},
$action = Notice::ACTION_EMAIL]
};
New::
hook Notice::policy(n: Notice::Info)
{
if ( n$note == SSH::Login && n$id$resp_h == 10.0.0.1 )
add n$actions[Notice::ACTION_EMAIL];
}
- notice() is now likewise a hook, no longer an event. If you have
handlers for that event, you'll likely just need to change the
type accordingly. Example:
Old::
event notice(n: Notice::Info) { ... }
New::
hook notice(n: Notice::Info) { ... }
- The notice_policy.log is gone. That's a result of the new notice
policy setup.
- Removed the byte_len() and length() bif functions. Use the ``|...|``
operator instead.
- The SSH::Login notice has been superseded by an corresponding
intelligence framework observation (SSH::SUCCESSFUL_LOGIN).
- PacketFilter::all_packets has been replaced with
PacketFilter::enable_auto_protocol_capture_filters.
- We removed the BitTorrent DPD signatures pending further updates to
that analyzer.
Bro 2.1
=======
New Functionality
-----------------
- Bro now comes with extensive IPv6 support. Past versions offered
only basic IPv6 functionality that was rarely used in practice as it
had to be enabled explicitly. IPv6 support is now fully integrated
into all parts of Bro including protocol analysis and the scripting
language. It's on by default and no longer requires any special
configuration.
Some of the most significant enhancements include support for IPv6
fragment reassembly, support for following IPv6 extension header
chains, and support for tunnel decapsulation (6to4 and Teredo). The
DNS analyzer now handles AAAA records properly, and DNS lookups that
Bro itself performs now include AAAA queries, so that, for example,
the result returned by script-level lookups is a set that can
contain both IPv4 and IPv6 addresses. Support for the most common
ICMPv6 message types has been added. Also, the FTP EPSV and EPRT
commands are now handled properly. Internally, the way IP addresses
are stored has been improved, so Bro can handle both IPv4
and IPv6 by default without any special configuration.
In addition to Bro itself, the other Bro components have also been
made IPv6-aware by default. In particular, significant changes were
made to trace-summary, PySubnetTree, and Broccoli to support IPv6.
- Bro now decapsulates tunnels via its new tunnel framework located in
scripts/base/frameworks/tunnels. It currently supports Teredo,
AYIYA, IP-in-IP (both IPv4 and IPv6), and SOCKS. For all these, it
logs the outer tunnel connections in both conn.log and tunnel.log,
and then proceeds to analyze the inner payload as if it were not
tunneled, including also logging that session in conn.log. For
SOCKS, it generates a new socks.log in addition with more
information.
- Bro now features a flexible input framework that allows users to
integrate external information in real-time into Bro while it's
processing network traffic. The most direct use-case at the moment
is reading data from ASCII files into Bro tables, with updates
picked up automatically when the file changes during runtime. See
doc/input.rst for more information.
Internally, the input framework is structured around the notion of
"reader plugins" that make it easy to interface to different data
sources. We will add more in the future.
- BroControl now has built-in support for host-based load-balancing
when using either PF_RING, Myricom cards, or individual interfaces.
Instead of adding a separate worker entry in node.cfg for each Bro
worker process on each worker host, it is now possible to just
specify the number of worker processes on each host and BroControl
configures everything correctly (including any neccessary enviroment
variables for the balancers).
This change adds three new keywords to the node.cfg file (to be used
with worker entries): lb_procs (specifies number of workers on a
host), lb_method (specifies what type of load balancing to use:
pf_ring, myricom, or interfaces), and lb_interfaces (used only with
"lb_method=interfaces" to specify which interfaces to load-balance
on).
- Bro's default ASCII log format is not exactly the most efficient way
for storing and searching large volumes of data. An alternatives,
Bro now comes with experimental support for two alternative output
formats:
* DataSeries: an efficient binary format for recording structured
bulk data. DataSeries is developed and maintained at HP Labs.
See doc/logging-dataseries for more information.
* ElasticSearch: a distributed RESTful, storage engine and search
engine built on top of Apache Lucene. It scales very well, both
for distributed indexing and distributed searching. See
doc/logging-elasticsearch.rst for more information.
Note that at this point, we consider Bro's support for these two
formats as prototypes for collecting experience with alternative
outputs. We do not yet recommend them for production (but welcome
feedback!)
Changed Functionality
---------------------
The following summarizes the most important differences in existing
functionality. Note that this list is not complete, see CHANGES for
the full set.
- Changes in dependencies:
* Bro now requires CMake >= 2.6.3.
* On Linux, Bro now links in tcmalloc (part of Google perftools)
if found at configure time. Doing so can significantly improve
memory and CPU use.
On the other platforms, the new configure option
--enable-perftools can be used to enable linking to tcmalloc.
(Note that perftools's support for non-Linux platforms may be
less reliable).
- The configure switch --enable-brov6 is gone.
- DNS name lookups performed by Bro now also query AAAA records. The
results of the A and AAAA queries for a given hostname are combined
such that at the scripting layer, the name resolution can yield a
set with both IPv4 and IPv6 addresses.
- The connection compressor was already deprecated in 2.0 and has now
been removed from the code base.
- We removed the "match" statement, which was no longer used by any of
the default scripts, nor was it likely to be used by anybody anytime
soon. With that, "match" and "using" are no longer reserved keywords.
- The syntax for IPv6 literals changed from "2607:f8b0:4009:802::1012"
to "[2607:f8b0:4009:802::1012]". When an IP address variable or IP
address literal is enclosed in pipes (for example,
``|[fe80::db15]|``) the result is now the size of the address in
bits (32 for IPv4 and 128 for IPv6).
- Bro now spawns threads for doing its logging. From a user's
perspective not much should change, except that the OS may now show
a bunch of Bro threads.
- We renamed the configure option --enable-perftools to
--enable-perftools-debug to indicate that the switch is only relevant
for debugging the heap.
- Bro's ICMP analyzer now handles both IPv4 and IPv6 messages with a
joint set of events. The `icmp_conn` record got a new boolean field
'v6' that indicates whether the ICMP message is v4 or v6.
- Log postprocessor scripts get an additional argument indicating the
type of the log writer in use (e.g., "ascii").
- BroControl's make-archive-name script also receives the writer
type, but as its 2nd(!) argument. If you're using a custom version
of that script, you need to adapt it. See the shipped version for
details.
- Signature files can now be loaded via the new "@load-sigs"
directive. In contrast to the existing (and still supported)
signature_files constant, this can be used to load signatures
relative to the current script (e.g., "@load-sigs ./foo.sig").
- The options "tunnel_port" and "parse_udp_tunnels" have been removed.
Bro now supports decapsulating tunnels directly for protocols it
understands.
- ASCII logs now record the time when they were opened/closed at the
beginning and end of the file, respectively (wall clock). The
options LogAscii::header_prefix and LogAscii::include_header have
been renamed to LogAscii::meta_prefix and LogAscii::include_meta,
respectively.
- The ASCII writers "header_*" options have been renamed to "meta_*"
(because there's now also a footer).
- Some built-in functions have been removed: "addr_to_count" (use
"addr_to_counts" instead), "bro_has_ipv6" (this is no longer
relevant because Bro now always supports IPv6), "active_connection"
(use "connection_exists" instead), and "connection_record" (use
"lookup_connection" instead).
- The "NFS3::mode2string" built-in function has been renamed to
"file_mode".
- Some built-in functions have been changed: "exit" (now takes the
exit code as a parameter), "to_port" (now takes a string as
parameter instead of a count and transport protocol, but
"count_to_port" is still available), "connect" (now takes an
additional string parameter specifying the zone of a non-global IPv6
address), and "listen" (now takes three additional parameters to
enable listening on IPv6 addresses).
- Some Bro script variables have been renamed:
"LogAscii::header_prefix" has been renamed to
"LogAscii::meta_prefix", "LogAscii::include_header" has been renamed
to "LogAscii::include_meta".
- Some Bro script variables have been removed: "tunnel_port",
"parse_udp_tunnels", "use_connection_compressor",
"cc_handle_resets", "cc_handle_only_syns", and
"cc_instantiate_on_data".
- A couple events have changed: the "icmp_redirect" event now includes
the target and destination addresses and any Neighbor Discovery
options in the message, and the last parameter of the
"dns_AAAA_reply" event has been removed because it was unused.
- The format of the ASCII log files has changed very slightly. Two
new lines are automatically added, one to record the time when the
log was opened, and the other to record the time when the log was
closed.
- In BroControl, the option (in broctl.cfg) "CFlowAddr" was renamed to
"CFlowAddress".
Bro 2.0
=======
As the version number jump from 1.5 suggests, Bro 2.0 is a major
upgrade and lots of things have changed. Most importantly, we have
rewritten almost all of Bro's default scripts from scratch, using
quite different structure now and focusing more on operational
deployment. The result is a system that works much better "out of the
box", even without much initial site-specific configuration. The
down-side is that 1.x configurations will need to be adapted to work
with the new version. The two rules of thumb are:
(1) If you have written your own Bro scripts
that do not depend on any of the standard scripts formerly
found in ``policy/``, they will most likely just keep working
(although you might want to adapt them to use some of the new
features, like the new logging framework; see below).
(2) If you have custom code that depends on specifics of 1.x
default scripts (including most configuration tuning), that is
unlikely to work with 2.x. We recommend to start by using just
the new scripts first, and then port over any customizations
incrementally as necessary (they may be much easier to do now,
or even unnecessary). Send mail to the Bro user mailing list
if you need help.
Below we summarize changes from 1.x to 2.x in more detail. This list
isn't complete, see the ``CHANGES`` file in the distribution or
:doc:`here <changes>` for the full story.
Script Organization
-------------------
In versions before 2.0, Bro scripts were all maintained in a flat
directory called ``policy/`` in the source tree. This directory is now
renamed to ``scripts/`` and contains major subdirectories ``base/``,
``policy/``, and ``site/``, each of which may also be subdivided
further.
The contents of the new ``scripts/`` directory, like the old/flat
``policy/`` still gets installed under the ``share/bro``
subdirectory of the installation prefix path just like previous
versions. For example, if Bro was compiled like ``./configure
--prefix=/usr/local/bro && make && make install``, then the script
hierarchy can be found in ``/usr/local/bro/share/bro``.
The main
subdirectories of that hierarchy are as follows:
- ``base/`` contains all scripts that are loaded by Bro by default
(unless the ``-b`` command line option is used to run Bro in a
minimal configuration). Note that is a major conceptual change:
rather than not loading anything by default, Bro now uses an
extensive set of default scripts out of the box.
The scripts under this directory generally either accumulate/log
useful state/protocol information for monitored traffic, configure a
default/recommended mode of operation, or provide extra Bro
scripting-layer functionality that has no significant performance cost.
- ``policy/`` contains all scripts that a user will need to explicitly
tell Bro to load. These are scripts that implement
functionality/analysis that not all users may want to use and may have
more significant performance costs. For a new installation, you
should go through these and see what appears useful to load.
- ``site/`` remains a directory that can be used to store locally
developed scripts. It now comes with some preinstalled example
scripts that contain recommended default configurations going beyond
the ``base/`` setup. E.g. ``local.bro`` loads extra scripts from
``policy/`` and does extra tuning. These files can be customized in
place without being overwritten by upgrades/reinstalls, unlike
scripts in other directories.
With version 2.0, the default ``BROPATH`` is set to automatically
search for scripts in ``policy/``, ``site/`` and their parent
directory, but **not** ``base/``. Generally, everything under
``base/`` is loaded automatically, but for users of the ``-b`` option,
it's important to know that loading a script in that directory
requires the extra ``base/`` path qualification. For example, the
following two scripts:
* ``$PREFIX/share/bro/base/protocols/ssl/main.bro``
* ``$PREFIX/share/bro/policy/protocols/ssl/validate-certs.bro``
are referenced from another Bro script like:
.. code:: bro
@load base/protocols/ssl/main
@load protocols/ssl/validate-certs
Notice how ``policy/`` can be omitted as a convenience in the second
case. ``@load`` can now also use relative path, e.g., ``@load
../main``.
Logging Framework
-----------------
- The logs generated by scripts that ship with Bro are entirely redone
to use a standardized, machine parsable format via the new logging
framework. Generally, the log content has been restructured towards
making it more directly useful to operations. Also, several
analyzers have been significantly extended and thus now log more
information. Take a look at ``ssl.log``.
* A particular format change that may be useful to note is that the
``conn.log`` ``service`` field is derived from DPD instead of
well-known ports (while that was already possible in 1.5, it was
not the default).
* Also, ``conn.log`` now reports raw number of packets/bytes per
endpoint.
- The new logging framework makes it possible to extend, customize,
and filter logs very easily. See the :doc:`logging framework
</frameworks/logging>` for more information on usage.
- A common pattern found in the new scripts is to store logging stream
records for protocols inside the ``connection`` records so that
state can be collected until enough is seen to log a coherent unit
of information regarding the activity of that connection. This
state is now frequently seen/accessible in event handlers, for
example, like ``c$<protocol>`` where ``<protocol>`` is replaced by
the name of the protocol. This field is added to the ``connection``
record by ``redef``'ing it in a
``base/protocols/<protocol>/main.bro`` script.
- The logging code has been rewritten internally, with script-level
interface and output backend now clearly separated. While ASCII
logging is still the default, we will add further output types in
the future (binary format, direct database logging).
Notice Framework
----------------
The way users interact with "notices" has changed significantly in order
to make it easier to define a site policy and more extensible for adding
customized actions. See the :doc:`notice framework
</frameworks/notice>`.
New Default Settings
--------------------
- Dynamic Protocol Detection (DPD) is now enabled/loaded by default.
- The default packet filter now examines all packets instead of
dynamically building a filter based on which protocol analysis scripts
are loaded. See ``PacketFilter::all_packets`` for how to revert to old
behavior.
API Changes
-----------
- The ``@prefixes`` directive works differently now.
Any added prefixes are now searched for and loaded *after* all input
files have been parsed. After all input files are parsed, Bro
searches ``BROPATH`` for prefixed, flattened versions of all of the
parsed input files. For example, if ``lcl`` is in ``@prefixes``, and
``site.bro`` is loaded, then a file named ``lcl.site.bro`` that's in
``BROPATH`` would end up being automatically loaded as well. Packages
work similarly, e.g. loading ``protocols/http`` means a file named
``lcl.protocols.http.bro`` in ``BROPATH`` gets loaded automatically.
- The ``make_addr`` BIF now returns a ``subnet`` versus an ``addr``
Variable Naming
---------------
- ``Module`` is more widely used for namespacing. E.g. the new
``site.bro`` exports the ``local_nets`` identifier (among other
things) into the ``Site`` module.
- Identifiers may have been renamed to conform to new `scripting
conventions
<http://www.bro.org/development/howtos/script-conventions.html>`_
Removed Functionality
---------------------
We have remove a bunch of functionality that was rarely used and/or
had not been maintained for a while already:
- The ``net`` script data type.
- The ``alarm`` statement; use the notice framework instead.
- Trace rewriting.
- DFA state expiration in regexp engine.
- Active mapping.
- Native DAG support (may come back eventually)
- ClamAV support.
- The connection compressor is now disabled by default, and will
be removed in the future.
BroControl Changes
------------------
BroControl looks pretty much similar to the version coming with Bro 1.x,
but has been cleaned up and streamlined significantly internally.
BroControl has a new ``process`` command to process a trace on disk
offline using a similar configuration to what BroControl installs for
live analysis.
BroControl now has an extensive plugin interface for adding new
commands and options. Note that this is still considered experimental.
We have removed the ``analysis`` command, and BroControl currently
does not send daily alarm summaries anymore (this may be restored
later).
Development Infrastructure
--------------------------
Bro development has moved from using SVN to Git for revision control.
Users that want to use the latest Bro development snapshot by checking it out
from the source repositories should see the `development process
<http://www.bro.org/development/process.html>`_. Note that all the various
sub-components now reside in their own repositories. However, the
top-level Bro repository includes them as git submodules so it's easy
to check them all out simultaneously.
Bro now uses `CMake <http://www.cmake.org>`_ for its build system so
that is a new required dependency when building from source.
Bro now comes with a growing suite of regression tests in
``testing/``.
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