Re: How to see alerts generated by preprocessors?

[Todd Wease <twease () sourcefire com>]

Hi Benjamin,

Can you try running without doing checksums:

$ snort -A console -c /etc/snort.conf -l /root/snortlog/ -k none -K ascii

(you got -k and -K mixed up)

It might be, if you're doing the telnet session from the same computer
that snort is running on, that checksum offloading is occurring and the
client TCP checksums haven't been calculated when the packets get to Snort.

Also, depending on how you compiled Snort (--enable-sourcefire or
--enable-decoder-preprocessor-rules), you might need to uncomment the
following line in your snort.conf:

# include $PREPROC_RULE_PATH/preprocessor.rules

Adjust this line if necessary:

var PREPROC_RULE_PATH ../preproc_rules


Todd


Benjamin Wagrocki wrote:
> Hello,
>
> I am a new snort user and I am having some problems to see alerts which 
> should be generated by the preprocessors. I simply do not see any event 
> on the console. (alarms generated by the detectionengine and the 
> signaturrules are working fine)
>
> For instance my smtp_preprocessor config looks like this:
> preprocessor smtp: \
> ports { 25 587 691 } \
> inspection_type stateful \
> normalize cmds \
> normalize_cmds { EXPN VRFY RCPT } \
> alt_max_command_line_len 2 { MAIL } \
> alt_max_command_line_len 300 { RCPT } \
> alt_max_command_line_len 500 { HELP HELO ETRN } \
> alt_max_command_line_len 255 { EXPN VRFY } \
> invalid_cmds { HELP } \
> alert_unknown_cmds
>
> As you can see, the MAIL command may only be 2 characters long and the 
> command HELP is not allowed.
>
> But when I do a telnet connection over port 25 to a mailserver, and then 
> use a longer mail from command or the help command no alerts are generated!
>
> I am running snort 2.8.3.2 on CentOS5. I also tried snort on windows xp.
>
> Snort is started this way:
> snort -A console -c /etc/snort.conf -l /root/snortlog/ -k ascii
>
> Here is my whole snort.conf:
>
> #--------------------------------------------------
> # http://www.snort.org Snort 2.8.3.2 Ruleset
> # Contact: snort-sigs () lists sourceforge net
> #--------------------------------------------------
> # $Id$
> #
> ###################################################
> # This file contains a sample snort configuration.
> # You can take the following steps to create your own custom configuration:
> #
> # 1) Set the variables for your network
> # 2) Configure dynamic loaded libraries
> # 3) Configure preprocessors
> # 4) Configure output plugins
> # 5) Add any runtime config directives
> # 6) Customize your rule set
> #
> ###################################################
> # Step #1: Set the network variables:
> #
> # You must change the following variables to reflect your local network. 
> The
> # variable is currently setup for an RFC 1918 address space.
> #
> # You can specify it explicitly as:
> #
> # var HOME_NET 10.1.1.0/24
> #
> # or use global variable $_ADDRESS which will be always
> # initialized to IP address and netmask of the network interface which 
> you run
> # snort at. Under Windows, this must be specified as
> # $(_ADDRESS), such as:
> # $(\Device\Packet_{12345678-90AB-CDEF-1234567890AB}_ADDRESS)
> #
> # var HOME_NET $eth0_ADDRESS
> #
> # You can specify lists of IP addresses for HOME_NET
> # by separating the IPs with commas like this:
> #
> # var HOME_NET [10.1.1.0/24,192.168.1.0/24]
> #
> # MAKE SURE YOU DON'T PLACE ANY SPACES IN YOUR LIST!
> #
> # or you can specify the variable to be any IP address
> # like this:
>
> var HOME_NET any
>
> # Set up the external network addresses as well. A good start may be "any"
> var EXTERNAL_NET any
>
> # Configure your server lists. This allows snort to only look for 
> attacks to
> # systems that have a service up. Why look for HTTP attacks if you are not
> # running a web server? This allows quick filtering based on IP addresses
> # These configurations MUST follow the same configuration scheme as defined
> # above for $HOME_NET.
>
> # List of DNS servers on your network
> var DNS_SERVERS $HOME_NET
>
> # List of SMTP servers on your network
> var SMTP_SERVERS $HOME_NET
>
> # List of web servers on your network
> var HTTP_SERVERS $HOME_NET
>
> # List of sql servers on your network
> var SQL_SERVERS $HOME_NET
>
> # List of telnet servers on your network
> var TELNET_SERVERS $HOME_NET
>
> # List of snmp servers on your network
> var SNMP_SERVERS $HOME_NET
>
> # Configure your service ports. This allows snort to look for attacks 
> destined
> # to a specific application only on the ports that application runs on. For
> # example, if you run a web server on port 8081, set your HTTP_PORTS 
> variable
> # like this:
> #
> # portvar HTTP_PORTS 8081
> #
> # Ports you run web servers on
> portvar HTTP_PORTS 80
>
> # NOTE: If you wish to define multiple HTTP ports, use the portvar
> # syntax to represent lists of ports and port ranges. Examples:
> ## portvar HTTP_PORTS [80,8080]
> ## portvar HTTP_PORTS [80,8000:8080]
> # And only include the rule that uses $HTTP_PORTS once.
> #
> # The pre-2.8.0 approach of redefining the variable to a different port and
> # including the rules file twice is obsolete. See README.variables for more
> # details.
>
> # Ports you want to look for SHELLCODE on.
> portvar SHELLCODE_PORTS !80
>
> # Ports you might see oracle attacks on
> portvar ORACLE_PORTS 1521
>
> # other variables
> #
> # AIM servers. AOL has a habit of adding new AIM servers, so instead of
> # modifying the signatures when they do, we add them to this list of 
> servers.
> var AIM_SERVERS 
> [64.12.24.0/23,64.12.28.0/23,64.12.161.0/24,64.12.163.0/24,64.12.200.0/24,205.188.3.0/24,205.188.5.0/24,205.188.7.0/24,205.188.9.0/24,205.188.153.0/24,205.188.179.0/24,205.188.248.0/24]
>  
>
>
> # Path to your rules files (this can be a relative path)
> # Note for Windows users: You are advised to make this an absolute path,
> # such as: c:\snort\rules
> var RULE_PATH /etc/snort/rules
> var PREPROC_RULE_PATH ../preproc_rules
>
> # Configure the snort decoder
> # ============================
> #
> # Snort's decoder will alert on lots of things such as header
> # truncation or options of unusual length or infrequently used tcp options
> #
> #
> # Stop generic decode events:
> #
> # config disable_decode_alerts
> #
> # Stop Alerts on experimental TCP options
> #
> # config disable_tcpopt_experimental_alerts
> #
> # Stop Alerts on obsolete TCP options
> #
> # config disable_tcpopt_obsolete_alerts
> #
> # Stop Alerts on T/TCP alerts
> #
> # In snort 2.0.1 and above, this only alerts when a TCP option is detected
> # that shows T/TCP being actively used on the network. If this is normal
> # behavior for your network, disable the next option.
> #
> # config disable_tcpopt_ttcp_alerts
> #
> # Stop Alerts on all other TCPOption type events:
> #
> # config disable_tcpopt_alerts
> #
> # Stop Alerts on invalid ip options
> #
> # config disable_ipopt_alerts
> #
> # Alert if value in length field (IP, TCP, UDP) is greater than the
> # actual length of the captured portion of the packet that the length
> # is supposed to represent:
> #
> # config enable_decode_oversized_alerts
> #
> # Same as above, but drop packet if in Inline mode -
> # enable_decode_oversized_alerts must be enabled for this to work:
> #
> # config enable_decode_oversized_drops
> #
>
> # Configure the detection engine
> # ===============================
> #
> # Use a different pattern matcher in case you have a machine with very 
> limited
> # resources:
> #
> # config detection: search-method lowmem
>
> # Configure Inline Resets
> # ========================
> #
> # If running an iptables firewall with snort in InlineMode() we can now
> # perform resets via a physical device. We grab the indev from iptables
> # and use this for the interface on which to send resets. This config
> # option takes an argument for the src mac address you want to use in the
> # reset packet. This way the bridge can remain stealthy. If the src mac
> # option is not set we use the mac address of the indev device. If we
> # don't set this option we will default to sending resets via raw socket,
> # which needs an ipaddress to be assigned to the int.
> #
> # config layer2resets: 00:06:76:DD:5F:E3
>
> ###################################################
> # Step #2: Configure dynamic loaded libraries
> #
> # If snort was configured to use dynamically loaded libraries,
> # those libraries can be loaded here.
> #
> # Each of the following configuration options can be done via
> # the command line as well.
> #
> # Load all dynamic preprocessors from the install path
> # (same as command line option --dynamic-preprocessor-lib-dir)
> #
> dynamicpreprocessor directory /usr/lib/snort-2.8.3.2_dynamicpreprocessor/
> #
> # Load a specific dynamic preprocessor library from the install path
> # (same as command line option --dynamic-preprocessor-lib)
> #
> # dynamicpreprocessor file 
> /usr/local/lib/snort_dynamicpreprocessor/libdynamicexample.so
> #
> # Load a dynamic engine from the install path
> # (same as command line option --dynamic-engine-lib)
> #
> dynamicengine /usr/lib/snort-2.8.3.2_dynamicengine/libsf_engine.so
> #
> # Load all dynamic rules libraries from the install path
> # (same as command line option --dynamic-detection-lib-dir)
> #
> # dynamicdetection directory /usr/local/lib/snort_dynamicrule/
> #
> # Load a specific dynamic rule library from the install path
> # (same as command line option --dynamic-detection-lib)
> #
> # dynamicdetection file 
> /usr/local/lib/snort_dynamicrule/libdynamicexamplerule.so
> #
>
> ###################################################
> # Step #3: Configure preprocessors
> #
> # General configuration for preprocessors is of
> # the form
> # preprocessor :
>
> # Configure Flow tracking module
> # -------------------------------
> #
> # The Flow tracking module is meant to start unifying the state keeping
> # mechanisms of snort into a single place. Right now, only a portscan 
> detector
> # is implemented but in the long term, many of the stateful subsystems of
> # snort will be migrated over to becoming flow plugins. This must be 
> enabled
> # for flow-portscan to work correctly.
> #
> # See README.flow for additional information
> #
> #preprocessor flow: stats_interval 0 hash 2
>
> # frag3: Target-based IP defragmentation
> # --------------------------------------
> #
> # Frag3 is a brand new IP defragmentation preprocessor that is capable of
> # performing "target-based" processing of IP fragments. Check out the
> # README.frag3 file in the doc directory for more background and 
> configuration
> # information.
> #
> # Frag3 configuration is a two step process, a global initialization phase
> # followed by the definition of a set of defragmentation engines.
> #
> # Global configuration defines the number of fragmented packets that 
> Snort can
> # track at the same time and gives you options regarding the memory cap 
> for the
> # subsystem or, optionally, allows you to preallocate all the memory for 
> the
> # entire frag3 system.
> #
> # frag3_global options:
> # max_frags: Maximum number of frag trackers that may be active at once.
> # Default value is 8192.
> # memcap: Maximum amount of memory that frag3 may access at any given time.
> # Default value is 4MB.
> # prealloc_frags: Maximum number of individual fragments that may be 
> processed
> # at once. This is instead of the memcap system, uses static
> # allocation to increase performance. No default value. Each
> # preallocated fragment typically eats ~1550 bytes. However,
> # the exact amount is determined by the snaplen, and this can
> # go as high as 64K so beware!
> #
> # Target-based behavior is attached to an engine as a "policy" for handling
> # overlaps and retransmissions as enumerated in the Paxson paper. There are
> # currently five policy types available: "BSD", "BSD-right", "First", 
> "Linux"
> # and "Last". Engines can be bound to standard Snort CIDR blocks or
> # IP lists.
> #
> # frag3_engine options:
> # timeout: Amount of time a fragmented packet may be active before 
> expiring.
> # Default value is 60 seconds.
> # ttl_limit: Limit of delta allowable for TTLs of packets in the fragments.
> # Based on the initial received fragment TTL.
> # min_ttl: Minimum acceptable TTL for a fragment, frags with TTLs below 
> this
> # value will be discarded. Default value is 0.
> # detect_anomalies: Activates frag3's anomaly detection mechanisms.
> # policy: Target-based policy to assign to this engine. Default is BSD.
> # bind_to: IP address set to bind this engine to. Default is all hosts.
> #
> # Frag3 configuration example:
> #preprocessor frag3_global: max_frags 65536, prealloc_frags 65536
> #preprocessor frag3_engine: policy linux \
> # bind_to [10.1.1.12/32,10.1.1.13/32] \
> # detect_anomalies
> #preprocessor frag3_engine: policy first \
> # bind_to 10.2.1.0/24 \
> # detect_anomalies
> #preprocessor frag3_engine: policy last \
> # bind_to 10.3.1.0/24
> #preprocessor frag3_engine: policy bsd
>
> preprocessor frag3_global: max_frags 65536
> preprocessor frag3_engine: policy first detect_anomalies
>
>
> # stream4: stateful inspection/stream reassembly for Snort
> #----------------------------------------------------------------------
> # Use in concert with the -z [all|est] command line switch to defeat 
> stick/snot
> # against TCP rules. Also performs full TCP stream reassembly, stateful
> # inspection of TCP streams, etc. Can statefully detect various portscan
> # types, fingerprinting, ECN, etc.
>
> # stateful inspection directive
> # no arguments loads the defaults (timeout 30, memcap 838860Cool
> # options (options are comma delimited):
> # detect_scans - stream4 will detect stealth portscans and generate alerts
> # when it sees them when this option is set
> # detect_state_problems - detect TCP state problems, this tends to be very
> # noisy because there are a lot of crappy ip stack
> # implementations out there
> #
> # disable_evasion_alerts - turn off the possibly noisy mitigation of
> # overlapping sequences.
> #
> # ttl_limit [number] - differential of the initial ttl on a session versus
> # the normal that someone may be playing games.
> # Routing flap may cause lots of false positives.
> #
> # keepstats [machine|binary] - keep session statistics, add "machine" to
> # get them in a flat format for machine reading, add
> # "binary" to get them in a unified binary output
> # format
> # noinspect - turn off stateful inspection only
> # timeout [number] - set the session timeout counter to [number] seconds,
> # default is 30 seconds
> # max_sessions [number] - limit the number of sessions stream4 keeps
> # track of
> # memcap [number] - limit stream4 memory usage to [number] bytes (does
> # not include session tracking, which is set by the
> # max_sessions option)
> # log_flushed_streams - if an event is detected on a stream this option 
> will
> # cause all packets that are stored in the stream4
> # packet buffers to be flushed to disk. This only
> # works when logging in pcap mode!
> # server_inspect_limit [bytes] - Byte limit on server side inspection.
> # enable_udp_sessions - turn on tracking of "sessions" over UDP. Requires
> # configure --enable-stream4udp. UDP sessions are
> # only created when there is a rule for the sender or
> # responder that has a flow or flowbits keyword.
> # max_udp_sessions [number] - limit the number of simultaneous UDP sessions
> # to track
> # udp_ignore_any - Do not inspect UDP packets unless there is a port 
> specific
> # rule for a given port. This is a performance improvement
> # and turns off inspection for udp xxx any -> xxx any rules
> # cache_clean_sessions [number] - Cleanup the session cache by number 
> sessions
> # at a time. The larger the value, the
> # more sessions are purged from the cache when
> # the session limit or memcap is reached.
> # Defaults to 5.
> #
> #
> #
> # Stream4 uses Generator ID 111 and uses the following SIDS
> # for that GID:
> # SID Event description
> # ----- -------------------
> # 1 Stealth activity
> # 2 Evasive RST packet
> # 3 Evasive TCP packet retransmission
> # 4 TCP Window violation
> # 5 Data on SYN packet
> # 6 Stealth scan: full XMAS
> # 7 Stealth scan: SYN-ACK-PSH-URG
> # 8 Stealth scan: FIN scan
> # 9 Stealth scan: NULL scan
> # 10 Stealth scan: NMAP XMAS scan
> # 11 Stealth scan: Vecna scan
> # 12 Stealth scan: NMAP fingerprint scan stateful detect
> # 13 Stealth scan: SYN-FIN scan
> # 14 TCP forward overlap
>
> #preprocessor stream4: disable_evasion_alerts
>
> # tcp stream reassembly directive
> # no arguments loads the default configuration
> # Only reassemble the client,
> # Only reassemble the default list of ports (See below),
> # Give alerts for "bad" streams
> #
> # Available options (comma delimited):
> # clientonly - reassemble traffic for the client side of a connection only
> # serveronly - reassemble traffic for the server side of a connection only
> # both - reassemble both sides of a session
> # noalerts - turn off alerts from the stream reassembly stage of stream4
> # ports [list] - use the space separated list of ports in [list], "all"
> # will turn on reassembly for all ports, "default" will turn
> # on reassembly for ports 21, 23, 25, 42, 53, 80, 110,
> # 111, 135, 136, 137, 139, 143, 445, 513, 514, 1433, 1521,
> # 2401, and 3306
> # favor_old - favor an old segment (based on sequence number) over a new 
> one.
> # This is the default.
> # favor_new - favor an new segment (based on sequence number) over an 
> old one.
> # overlap_limit [number] - limit on overlaping segments for a session.
> # flush_on_alert - flushes stream when an alert is generated for a session.
> # flush_behavior [mode] -
> # default - use old static flushpoints (default)
> # large_window - use new larger static flushpoints
> # random - use random flushpoints defined by flush_base,
> # flush_seed and flush_range
> # flush_base [number] - lowest allowed random flushpoint (512 by default)
> # flush_range [number] - number is the space within which random 
> flushpoints
> # are generated (default 1213)
> # flush_seed [number] - seed for the random number generator, defaults to
> # Snort PID + time
> #
> # Using the default random flushpoints, the smallest flushpoint is 512,
> # and the largest is 1725 bytes.
> #preprocessor stream4_reassemble
>
> # stream5: Target Based stateful inspection/stream reassembly for Snort
> # ---------------------------------------------------------------------
> # Stream5 is a target-based stream engine for Snort. Its functionality
> # replaces that of Stream4. Consequently, BOTH Stream4 and Stream5
> # cannot be used simultaneously. Comment out the stream4 configurations
> # above to use Stream5.
> #
> # See README.stream5 for details on the configuration options.
> #
> # Example config (that emulates Stream4 with UDP support compiled in)
> preprocessor stream5_global: max_tcp 8192, track_tcp yes, \
> track_udp no
> preprocessor stream5_tcp: policy first, use_static_footprint_sizes
> # preprocessor stream5_udp: ignore_any_rules
>
>
> # Performance Statistics
> # ----------------------
> # Documentation for this is provided in the Snort Manual. You should 
> read it.
> # It is included in the release distribution as doc/snort_manual.pdf
> #
> # preprocessor perfmonitor: time 300 file /var/snort/snort.stats pktcnt 
> 10000
>
> # http_inspect: normalize and detect HTTP traffic and protocol anomalies
> #
> # lots of options available here. See doc/README.http_inspect.
> # unicode.map should be wherever your snort.conf lives, or given
> # a full path to where snort can find it.
> preprocessor http_inspect: global \
> iis_unicode_map unicode.map 1252
>
> preprocessor http_inspect_server: server default \
> profile all ports { 80 8080 8180 } oversize_dir_length 500
>
> #
> # Example unique server configuration
> #
> #preprocessor http_inspect_server: server 1.1.1.1 \
> # ports { 80 3128 8080 } \
> # server_flow_depth 0 \
> # ascii no \
> # double_decode yes \
> # non_rfc_char { 0x00 } \
> # chunk_length 500000 \
> # non_strict \
> # oversize_dir_length 300 \
> # no_alerts
>
>
> # rpc_decode: normalize RPC traffic
> # ---------------------------------
> # RPC may be sent in alternate encodings besides the usual 4-byte encoding
> # that is used by default. This plugin takes the port numbers that RPC
> # services are running on as arguments - it is assumed that the given ports
> # are actually running this type of service. If not, change the ports or 
> turn
> # it off.
> # The RPC decode preprocessor uses generator ID 106
> #
> # arguments: space separated list
> # alert_fragments - alert on any rpc fragmented TCP data
> # no_alert_multiple_requests - don't alert when >1 rpc query is in a packet
> # no_alert_large_fragments - don't alert when the fragmented
> # sizes exceed the current packet size
> # no_alert_incomplete - don't alert when a single segment
> # exceeds the current packet size
>
> preprocessor rpc_decode: 111 32771
>
> # bo: Back Orifice detector
> # -------------------------
> # Detects Back Orifice traffic on the network.
> #
> # arguments:
> # syntax:
> # preprocessor bo: noalert { client | server | general | snort_attack } \
> # drop { client | server | general | snort_attack }
> # example:
> # preprocessor bo: noalert { general server } drop { snort_attack }
> #
> #
> # The Back Orifice detector uses Generator ID 105 and uses the
> # following SIDS for that GID:
> # SID Event description
> # ----- -------------------
> # 1 Back Orifice traffic detected
> # 2 Back Orifice Client Traffic Detected
> # 3 Back Orifice Server Traffic Detected
> # 4 Back Orifice Snort Buffer Attack
>
> preprocessor bo
>
> # ftp_telnet: FTP & Telnet normalizer, protocol enforcement and buff 
> overflow
> # 
> ---------------------------------------------------------------------------
> # This preprocessor normalizes telnet negotiation strings from telnet and
> # ftp traffic. It looks for traffic that breaks the normal data stream
> # of the protocol, replacing it with a normalized representation of that
> # traffic so that the "content" pattern matching keyword can work without
> # requiring modifications.
> #
> # It also performs protocol correctness checks for the FTP command channel,
> # and identifies open FTP data transfers.
> #
> # FTPTelnet has numerous options available, please read
> # README.ftptelnet for help configuring the options for the global
> # telnet, ftp server, and ftp client sections for the protocol.
>
> #####
> # Per Step #2, set the following to load the ftptelnet preprocessor
> # dynamicpreprocessor file
> # or use commandline option
> # --dynamic-preprocessor-lib
>
> preprocessor ftp_telnet: global \
> encrypted_traffic yes \
> inspection_type stateful
>
> preprocessor ftp_telnet_protocol: telnet \
> normalize \
> ayt_attack_thresh 200
>
> # This is consistent with the FTP rules as of 18 Sept 2004.
> # CWD can have param length of 200
> # MODE has an additional mode of Z (compressed)
> # Check for string formats in USER & PASS commands
> # Check nDTM commands that set modification time on the file.
> preprocessor ftp_telnet_protocol: ftp server default \
> def_max_param_len 100 \
> alt_max_param_len 200 { CWD } \
> cmd_validity MODE < char ASBCZ > \
> cmd_validity MDTM < [ date nnnnnnnnnnnnnn[.n[n[n]]] ] string > \
> chk_str_fmt { USER PASS RNFR RNTO SITE MKD } \
> telnet_cmds yes \
> data_chan
>
> preprocessor ftp_telnet_protocol: ftp client default \
> max_resp_len 256 \
> bounce yes \
> telnet_cmds yes
>
> # smtp: SMTP normalizer, protocol enforcement and buffer overflow
> # 
> ---------------------------------------------------------------------------
> # This preprocessor normalizes SMTP commands by removing extraneous spaces.
> # It looks for overly long command lines, response lines, and data 
> header lines.
> # It can alert on invalid commands, or specific valid commands. It can 
> optionally
> # ignore mail data, and can ignore TLS encrypted data.
> #
> # SMTP has numerous options available, please read README.SMTP for help
> # configuring options.
>
> #####
> # Per Step #2, set the following to load the smtp preprocessor
> # dynamicpreprocessor file
> # or use commandline option
> # --dynamic-preprocessor-lib
>
> preprocessor smtp: \
> ports { 25 587 691 } \
> inspection_type stateful \
> normalize cmds \
> normalize_cmds { EXPN VRFY RCPT } \
> alt_max_command_line_len 2 { MAIL } \
> alt_max_command_line_len 300 { RCPT } \
> alt_max_command_line_len 500 { HELP HELO ETRN } \
> alt_max_command_line_len 255 { EXPN VRFY } \
> invalid_cmds { HELP } \
> alert_unknown_cmds
>
> # sfPortscan
> # ----------
> # Portscan detection module. Detects various types of portscans and
> # portsweeps. For more information on detection philosophy, alert types,
> # and detailed portscan information, please refer to the README.sfportscan.
> #
> # -configuration options-
> # proto { tcp udp icmp ip all }
> # The arguments to the proto option are the types of protocol scans that
> # the user wants to detect. Arguments should be separated by spaces and
> # not commas.
> # scan_type { portscan portsweep decoy_portscan distributed_portscan all }
> # The arguments to the scan_type option are the scan types that the
> # user wants to detect. Arguments should be separated by spaces and not
> # commas.
> # sense_level { low|medium|high }
> # There is only one argument to this option and it is the level of
> # sensitivity in which to detect portscans. The 'low' sensitivity
> # detects scans by the common method of looking for response errors, such
> # as TCP RSTs or ICMP unreachables. This level requires the least
> # tuning. The 'medium' sensitivity level detects portscans and
> # filtered portscans (portscans that receive no response). This
> # sensitivity level usually requires tuning out scan events from NATed
> # IPs, DNS cache servers, etc. The 'high' sensitivity level has
> # lower thresholds for portscan detection and a longer time window than
> # the 'medium' sensitivity level. Requires more tuning and may be noisy
> # on very active networks. However, this sensitivity levels catches the
> # most scans.
> # memcap { positive integer }
> # The maximum number of bytes to allocate for portscan detection. The
> # higher this number the more nodes that can be tracked.
> # logfile { filename }
> # This option specifies the file to log portscan and detailed portscan
> # values to. If there is not a leading /, then snort logs to the
> # configured log directory. Refer to README.sfportscan for details on
> # the logged values in the logfile.
> # watch_ip { Snort IP List }
> # ignore_scanners { Snort IP List }
> # ignore_scanned { Snort IP List }
> # These options take a snort IP list as the argument. The 'watch_ip'
> # option specifies the IP(s) to watch for portscan. The
> # 'ignore_scanners' option specifies the IP(s) to ignore as scanners.
> # Note that these hosts are still watched as scanned hosts. The
> # 'ignore_scanners' option is used to tune alerts from very active
> # hosts such as NAT, nessus hosts, etc. The 'ignore_scanned' option
> # specifies the IP(s) to ignore as scanned hosts. Note that these hosts
> # are still watched as scanner hosts. The 'ignore_scanned' option is
> # used to tune alerts from very active hosts such as syslog servers, etc.
> # detect_ack_scans
> # This option will include sessions picked up in midstream by the stream
> # module, which is necessary to detect ACK scans. However, this can lead to
> # false alerts, especially under heavy load with dropped packets; which 
> is why
> # the option is off by default.
> #
> preprocessor sfportscan: proto { all } \
> memcap { 10000000 } \
> sense_level { low }
>
> # arpspoof
> #----------------------------------------
> # Experimental ARP detection code from Jeff Nathan, detects ARP attacks,
> # unicast ARP requests, and specific ARP mapping monitoring. To make use of
> # this preprocessor you must specify the IP and hardware address of 
> hosts on
> # the same layer 2 segment as you. Specify one host IP MAC combo per line.
> # Also takes a "-unicast" option to turn on unicast ARP request detection.
> # Arpspoof uses Generator ID 112 and uses the following SIDS for that GID:
>
> # SID Event description
> # ----- -------------------
> # 1 Unicast ARP request
> # 2 Etherframe ARP mismatch (src)
> # 3 Etherframe ARP mismatch (dst)
> # 4 ARP cache overwrite attack
>
> #preprocessor arpspoof
> #preprocessor arpspoof_detect_host: 192.168.40.1 f0:0f:00:f0:0f:00
>
> # ssh
> #----------------------------------------
> # EXPERIMENTAL CODE!!!
> #
> # THIS CODE IS STILL EXPERIMENTAL AND MAY OR MAY NOT BE STABLE!
> # USE AT YOUR OWN RISK! DO NOT USE IN PRODUCTION ENVIRONMENTS.
> # YOU HAVE BEEN WARNED.
> #
> # The SSH preprocessor detects the following exploits: Gobbles, CRC 32,
> # Secure CRT, and the Protocol Mismatch exploit.
> #
> # Both Gobbles and CRC 32 attacks occur after the key exchange, and are
> # therefore encrypted. Both attacks involve sending a large payload
> # (20kb+) to the server immediately after the authentication challenge.
> # To detect the attacks, the SSH preprocessor counts the number of bytes
> # transmitted to the server. If those bytes exceed a pre-defined limit
> # within a pre-define number of packets, an alert is generated. Since
> # Gobbles only effects SSHv2 and CRC 32 only effects SSHv1, the SSH
> # version string exchange is used to distinguish the attacks.
> #
> # The Secure CRT and protocol mismatch exploits are observable before
> # the key exchange.
> #
> # SSH has numerous options available, please read README.ssh for help
> # configuring options.
>
> #####
> # Per Step #2, set the following to load the ssh preprocessor
> # dynamicpreprocessor file
> # or use commandline option
> # --dynamic-preprocessor-lib
> #
> #preprocessor ssh: server_ports { 22 } \
> # max_client_bytes 19600 \
> # max_encrypted_packets 20
>
> # DCE/RPC
> #----------------------------------------
> #
> # The dcerpc preprocessor detects and decodes SMB and DCE/RPC traffic.
> # It is primarily interested in DCE/RPC data, and only decodes SMB
> # to get at the DCE/RPC data carried by the SMB layer.
> #
> # Currently, the preprocessor only handles reassembly of fragmentation
> # at both the SMB and DCE/RPC layer. Snort rules can be evaded by
> # using both types of fragmentation; with the preprocessor enabled
> # the rules are given a buffer with a reassembled SMB or DCE/RPC
> # packet to examine.
> #
> # At the SMB layer, only fragmentation using WriteAndX is currently
> # reassembled. Other methods will be handled in future versions of
> # the preprocessor.
> #
> # Autodetection of SMB is done by looking for "\xFFSMB" at the start of
> # the SMB data, as well as checking the NetBIOS header (which is always
> # present for SMB) for the type "SMB Session".
> #
> # Autodetection of DCE/RPC is not as reliable. Currently, two bytes are
> # checked in the packet. Assuming that the data is a DCE/RPC header,
> # one byte is checked for DCE/RPC version (5) and another for the type
> # "DCE/RPC Request". If both match, the preprocessor proceeds with that
> # assumption that it is looking at DCE/RPC data. If subsequent checks
> # are nonsensical, it ends processing.
> #
> # DCERPC has numerous options available, please read README.dcerpc for help
> # configuring options.
>
> #####
> # Per Step #2, set the following to load the dcerpc preprocessor
> # dynamicpreprocessor file
> # or use commandline option
> # --dynamic-preprocessor-lib
>
> preprocessor dcerpc: \
> autodetect \
> max_frag_size 3000 \
> memcap 100000
>
> # DNS
> #----------------------------------------
> # The dns preprocessor (currently) decodes DNS Response traffic
> # and detects a few vulnerabilities.
> #
> # DNS has a few options available, please read README.dns for
> # help configuring options.
>
> #####
> # Per Step #2, set the following to load the dns preprocessor
> # dynamicpreprocessor file
> # or use commandline option
> # --dynamic-preprocessor-lib
>
> preprocessor dns: \
> ports { 53 } \
> enable_rdata_overflow
>
> # SSL
> #----------------------------------------
> # Encrypted traffic should be ignored by Snort for both performance reasons
> # and to reduce false positives. The SSL Dynamic Preprocessor (SSLPP)
> # inspects SSL traffic and optionally determines if and when to stop
> # inspection of it.
> #
> # Typically, SSL is used over port 443 as HTTPS. By enabling the SSLPP to
> # inspect port 443, only the SSL handshake of each connection will be
> # inspected. Once the traffic is determined to be encrypted, no further
> # inspection of the data on the connection is made.
> #
> # Important note: Stream4 or Stream5 should be explicitly told to 
> reassemble
> # traffic on the ports that you intend to inspect SSL
> # encrypted traffic on.
> #
> # To add reassembly on port 443 to Stream5, use 'port both 443' in the
> # Stream5 configuration.
>
> preprocessor ssl: noinspect_encrypted
>
>
> ####################################################################
> # Step #4: Configure output plugins
> #
> # Uncomment and configure the output plugins you decide to use. General
> # configuration for output plugins is of the form:
> #
> # output :
> #
> # alert_syslog: log alerts to syslog
> # ----------------------------------
> # Use one or more syslog facilities as arguments. Win32 can also optionally
> # specify a particular hostname/port. Under Win32, the default hostname is
> # '127.0.0.1', and the default port is 514.
> #
> # [Unix flavours should use this format...]
> # output alert_syslog: LOG_AUTH LOG_ALERT
> #
> # [Win32 can use any of these formats...]
> # output alert_syslog: LOG_AUTH LOG_ALERT
> # output alert_syslog: host=hostname, LOG_AUTH LOG_ALERT
> # output alert_syslog: host=hostname:port, LOG_AUTH LOG_ALERT
>
> # log_tcpdump: log packets in binary tcpdump format
> # -------------------------------------------------
> # The only argument is the output file name.
> #
> # output log_tcpdump: tcpdump.log
>
> # database: log to a variety of databases
> # ---------------------------------------
> # See the README.database file for more information about configuring
> # and using this plugin.
> #
> # output database: log, mysql, user=root password=test dbname=db 
> host=localhost
> # output database: alert, postgresql, user=snort dbname=snort
> # output database: log, odbc, user=snort dbname=snort
> # output database: log, mssql, dbname=snort user=snort password=test
> # output database: log, oracle, dbname=snort user=snort password=test
>
> # unified: Snort unified binary format alerting and logging
> # -------------------------------------------------------------
> # The unified output plugin provides two new formats for logging and 
> generating
> # alerts from Snort, the "unified" format. The unified format is a straight
> # binary format for logging data out of Snort that is designed to be 
> fast and
> # efficient. Used with barnyard (the new alert/log processor), most of the
> # overhead for logging and alerting to various slow storage mechanisms 
> such as
> # databases or the network can now be avoided.
> #
> # Check out the spo_unified.h file for the data formats.
> #
> # Two arguments are supported.
> # filename - base filename to write to (current time_t is appended)
> # limit - maximum size of spool file in MB (default: 12Cool
> #
> # output alert_unified: filename snort.alert, limit 128
> # output log_unified: filename snort.log, limit 128
>
>
> # prelude: log to the Prelude Hybrid IDS system
> # ---------------------------------------------
> #
> # profile = Name of the Prelude profile to use (default is snort).
> #
> # Snort priority to IDMEF severity mappings:
> # high < medium < low < info
> #
> # These are the default mapped from classification.config:
> # info = 4
> # low = 3
> # medium = 2
> # high = anything below medium
> #
> # output alert_prelude
> # output alert_prelude: profile=snort-profile-name
>
>
> # You can optionally define new rule types and associate one or more output
> # plugins specifically to that type.
> #
> # This example will create a type that will log to just tcpdump.
> # ruletype suspicious
> # {
> # type log
> # output log_tcpdump: suspicious.log
> # }
> #
> # EXAMPLE RULE FOR SUSPICIOUS RULETYPE:
> # suspicious tcp $HOME_NET any -> $HOME_NET 6667 (msg:"Internal IRC 
> Server"Wink
> #
> # This example will create a rule type that will log to syslog and a mysql
> # database:
> # ruletype redalert
> # {
> # type alert
> # output alert_syslog: LOG_AUTH LOG_ALERT
> # output database: log, mysql, user=snort dbname=snort host=localhost
> # }
> #
> # EXAMPLE RULE FOR REDALERT RULETYPE:
> # redalert tcp $HOME_NET any -> $EXTERNAL_NET 31337 \
> # (msg:"Someone is being LEET"; flags:A+Wink
>
> #
> # Include classification & priority settings
> # Note for Windows users: You are advised to make this an absolute path,
> # such as: c:\snort\etc\classification.config
> #
>
> include classification.config
>
> #
> # Include reference systems
> # Note for Windows users: You are advised to make this an absolute path,
> # such as: c:\snort\etc\reference.config
> #
>
> include reference.config
>
> ####################################################################
> # Step #5: Configure snort with config statements
> #
> # See the snort manual for a full set of configuration references
> #
> # config flowbits_size: 64
> #
> # New global ignore_ports config option from Andy Mullican
> #
> # config ignore_ports:
> # config ignore_ports: tcp 21 6667:6671 1356
> # config ignore_ports: udp 1:17 53
>
>
> ####################################################################
> # Step #6: Customize your rule set
> #
> # Up to date snort rules are available at http://www.snort.org
> #
> # The snort web site has documentation about how to write your own 
> custom snort
> # rules.
>
> #=========================================
> # Include all relevant rulesets here
> #
> # The following rulesets are disabled by default:
> #
> # web-attacks, backdoor, shellcode, policy, porn, info, icmp-info, virus,
> # chat, multimedia, and p2p
> #
> # These rules are either site policy specific or require tuning in order 
> to not
> # generate false positive alerts in most enviornments.
> #
> # Please read the specific include file for more information and
> # README.alert_order for how rule ordering affects how alerts are 
> triggered.
> #=========================================
>
> #include $RULE_PATH/local.rules
> #include $RULE_PATH/bad-traffic.rules
> #include $RULE_PATH/exploit.rules
> #include $RULE_PATH/scan.rules
> #include $RULE_PATH/finger.rules
> #include $RULE_PATH/ftp.rules
> #include $RULE_PATH/telnet.rules
> #include $RULE_PATH/rpc.rules
> #include $RULE_PATH/rservices.rules
> #include $RULE_PATH/dos.rules
> #include $RULE_PATH/ddos.rules
> #include $RULE_PATH/dns.rules
> #include $RULE_PATH/tftp.rules
>
> #include $RULE_PATH/web-cgi.rules
> #include $RULE_PATH/web-coldfusion.rules
> #include $RULE_PATH/web-iis.rules
> #include $RULE_PATH/web-frontpage.rules
> #include $RULE_PATH/web-misc.rules
> #include $RULE_PATH/web-client.rules
> #include $RULE_PATH/web-php.rules
>
> #include $RULE_PATH/sql.rules
> #include $RULE_PATH/x11.rules
> #include $RULE_PATH/icmp.rules
> #include $RULE_PATH/netbios.rules
> #include $RULE_PATH/misc.rules
> #include $RULE_PATH/attack-responses.rules
> #include $RULE_PATH/oracle.rules
> #include $RULE_PATH/mysql.rules
> #include $RULE_PATH/snmp.rules
>
> #include $RULE_PATH/smtp.rules
> #include $RULE_PATH/imap.rules
> #include $RULE_PATH/pop2.rules
> #include $RULE_PATH/pop3.rules
>
> #include $RULE_PATH/nntp.rules
> #include $RULE_PATH/other-ids.rules
> # include $RULE_PATH/web-attacks.rules
> # include $RULE_PATH/backdoor.rules
> # include $RULE_PATH/shellcode.rules
> # include $RULE_PATH/policy.rules
> # include $RULE_PATH/porn.rules
> # include $RULE_PATH/info.rules
> # include $RULE_PATH/icmp-info.rules
> # include $RULE_PATH/virus.rules
> # include $RULE_PATH/chat.rules
> # include $RULE_PATH/multimedia.rules
> # include $RULE_PATH/p2p.rules
> # include $RULE_PATH/spyware-put.rules
> # include $RULE_PATH/specific-threats.rules
> #include $RULE_PATH/experimental.rules
> include $RULE_PATH/testing.rules
>
> # include $PREPROC_RULE_PATH/preprocessor.rules
> # include $PREPROC_RULE_PATH/decoder.rules
>
> # Include any thresholding or suppression commands. See threshold.conf 
> in the
> # /etc directory for details. Commands don't necessarily need to be
> # contained in this conf, but a separate conf makes it easier to 
> maintain them.
> # Note for Windows users: You are advised to make this an absolute path,
> # such as: c:\snort\etc\threshold.conf
> # Uncomment if needed.
> # include threshold.conf
>
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