Chapter 5: Introducing psad: The Port Scan Attack Detector
This chapter discusses installation and configuration of psad, and shows you why it is important to listen to the stories that iptables logs have to tell.You can download the default psad configuration files here as mentioned in Chapter 5. Each of these files is included within the psad source tar file as well, and the psad.conf file is displayed below:
#
##############################################################################
#
# This is the configuration file for psad (the Port Scan Attack Detector).
# Normally this file gets installed at /etc/psad/psad.conf, but can be put
# anywhere in the filesystem and then the path can be specified on the
# command line argument "-c <file>" to psad. All three psad daemons (psad,
# kmsgsd, and psadwatchd) reference this config file.
#
# Each line has the form "<variable name> <value>;". Note the semi-
# colon after the <value>. All characters after the semicolon will be
# ignored to provide space for comments.
#
##############################################################################
#
# $Id: index.html 2980 2011-01-09 15:27:41Z mbr $
#
### Supports multiple email addresses (as a comma separated
### list).
EMAIL_ADDRESSES root@localhost;
### Machine hostname
HOSTNAME _CHANGEME_;
### Specify the home and external networks. Note that by default the
### ENABLE_INTF_LOCAL_NETS is enabled, so psad automatically detects
### all of the directly connected subnets and uses this information as
#@@ the HOME_NET variable.
HOME_NET any;
EXTERNAL_NET any;
### The FW_SEARCH_ALL variable controls has psad will parse iptables
### messages. If it is set to "Y" then psad will parse all iptables
### messages for evidence of scan activity. If it is set to "N" then
### psad will only parse those iptables messages that contain logging
### prefixes specified by the FW_MSG_SEARCH variable below. Logging
### prefixes are set with the --log-prefix command line option to iptables.
### Setting FW_SEARCH_ALL to "N" is useful for having psad only analyze
### iptables messages that are logged out of a specific iptables chain
### (multiple strings can be searched for, see the comment above the
### FW_MSG_SEARCH variable below) or a specific logging rule for example.
### FW_SEARCH_ALL is set to "Y" by default since usually people want psad
### to parse all iptables messages.
FW_SEARCH_ALL Y;
### The FW_MSG_SEARCH variable can be modified to look for logging messages
### that are specific to your firewall configuration (specified by the
### "--log-prefix" option. For example, if your firewall uses the
### string "Audit" for packets that have been blocked, then you could
### set FW_MSG_SEARCH to "Audit"; The default string to search for is
### "DROP". Both psad and kmsgsd reference this file. NOTE: You can
### specify this variable multiple times to have psad search for multiple
### strings. For example to have psad search for the strings "Audit" and
### "Reject", you would use the following two lines:
#FW_MSG_SEARCH Audit;
#FW_MSG_SEARCH REJECT;
FW_MSG_SEARCH DROP;
### Set the type of syslog daemon that is used. The SYSLOG_DAEMON
### variable accepts four possible values: syslogd, syslog-ng, ulogd,
### or ### metalog.
SYSLOG_DAEMON syslogd;
### Danger levels. These represent the total number of
### packets required for a scan to reach each danger level.
### A scan may also reach a danger level if the scan trips
### a signature or if the scanning ip is listed in
### auto_ips so a danger level is automatically
### assigned.
DANGER_LEVEL1 5; ### Number of packets.
DANGER_LEVEL2 15;
DANGER_LEVEL3 150;
DANGER_LEVEL4 1500;
DANGER_LEVEL5 10000;
### Set the interval (in seconds) psad will use to sleep before
### checking for new iptables log messages
CHECK_INTERVAL 5;
### Search for snort "sid" values generated by fwsnort
### or snort2iptables
SNORT_SID_STR SID;
### Set the minimum range of ports that must be scanned before
### psad will send an alert. The default is 1 so that at
### least two port must be scanned (p2-p1 >= 1). This can be set
### to 0 if you want psad to be extra paranoid, or 30000 if not.
PORT_RANGE_SCAN_THRESHOLD 1;
### If "Y", means that scans will never timeout. This is useful
### for catching scans that take place over long periods of time
### where the attacker is trying to slip beneath the IDS thresholds.
ENABLE_PERSISTENCE Y;
### This is used only if ENABLE_PERSISTENCE = "N";
SCAN_TIMEOUT 3600; ### seconds
### If "Y", means all signatures will be shown since
### the scan started instead of just the current ones.
SHOW_ALL_SIGNATURES N;
### Allow reporting methods to be enabled/restricted. This keyword can
### accept values of "nosyslog" (don't write any messages to syslog),
### "noemail" (don't send any email messages), or "ALL" (to generate both
### syslog and email messages). "ALL" is the default. Both "nosyslog"
### and "noemail" can be combined with a comma to disable all logging
### and alerting.
ALERTING_METHODS ALL;
### When enabled, this instructs psad to write the "msg" field
### associated with Snort rule matches to syslog.
ENABLE_SIG_MSG_SYSLOG Y;
SIG_MSG_SYSLOG_THRESHOLD 10;
SIG_SID_SYSLOG_THRESHOLD 10;
### TTL values are decremented depending on the number of hops
### the packet has taken before it hits the firewall. We will
### assume packets will not jump through more than 20 hops on
### average.
MAX_HOPS 20;
### Do not include any timestamp included within kernel logging
### messages (Ubuntu systems commonly have this)
IGNORE_KERNEL_TIMESTAMP Y;
### FIXME: try to mitigate the affects of the iptables connection
### tracking bug by ignoring tcp packets that have the ack bit set.
### Read the "BUGS" section of the psad man page. Note that
### if a packet matches a snort SID generated by fwsnort (see
### http://www.cipherdyne.org/fwsnort/)
### then psad will see it even if the ack bit is set. See the
### SNORT_SID_STR variable.
IGNORE_CONNTRACK_BUG_PKTS Y;
### define a set of ports to ignore (this is useful particularly
### for port knocking applications since the knock sequence will
### look to psad like a scan). This variable may be defined as
### a comma-separated list of port numbers or port ranges and
### corresponding protocol, For example, to have psad ignore all
### tcp in the range 61000-61356 and udp ports 53 and 5000, use:
### IGNORE_PORTS tcp/61000-61356, udp/53, udp/5000;
IGNORE_PORTS NONE;
### allow entire protocols to be ignored. This keyword can accept
### a comma separated list of protocols. Each protocol must match
### the protocol that is specified in a Netfilter log message (case
### insensitively, so both "TCP" or "tcp" is ok).
### IGNORE_PROTOCOL tcp,udp;
IGNORE_PROTOCOLS NONE;
### allow packets to be ignored based on interface (this is the
### "IN" interface in Nefilter logging messages).
IGNORE_INTERFACES NONE;
### Ignore these specific logging prefixes
IGNORE_LOG_PREFIXES NONE;
### Minimum danger level a scan must reach before any logging or
### alerting is done. The EMAIL_ALERT_DANGER_LEVEL variable below
### only refers to email alerts; the MIN_DANGER_LEVEL variable
### applies to everything from email alerts to whether or not the
### IP directory is created within /var/log/psad/. Hence
### MIN_DANGER_LEVEL should be set less than or equal to the value
### assigned to the EMAIL_ALERT_DANGER_LEVEL variable.
MIN_DANGER_LEVEL 1;
### Only send email alert if danger level >= to this value.
EMAIL_ALERT_DANGER_LEVEL 1;
### Treat all subnets on local interfaces as part of HOME_NET (this
### means that these networks do not have to be manually defined)
ENABLE_INTF_LOCAL_NETS Y;
### Include MAC addresses in email alert
ENABLE_MAC_ADDR_REPORTING N;
### Look for the Netfilter logging rule (fwcheck_psad is executed)
ENABLE_FW_LOGGING_CHECK Y;
### Send no more than this number of emails for a single
### scanning source IP. Note that enabling this feature may cause
### alerts for real attacks to not be generated if an attack is sent
### after the email threshold has been reached for an IP address.
### This is why the default is set to "0".
EMAIL_LIMIT 0;
### If "Y", send a status email message when an IP has reached the
### EMAIL_LIMIT threshold.
EMAIL_LIMIT_STATUS_MSG Y;
### If "Y", send email for all newly logged packets from the same
### source ip instead of just when a danger level increases.
ALERT_ALL Y;
### If "Y", then psad will import old scan source ip directories
### as current scans instead of moving the directories into the
### archive directory.
IMPORT_OLD_SCANS N;
### syslog facility and priority (the defaults are usually ok)
### The SYSLOG_FACILITY variable can be set to one of LOG_LOCAL{0-7}, and
### SYSLOG_PRIORITY can be set to one of LOG_INFO, LOG_DEBUG, LOG_NOTICE,
### LOG_WARNING, LOG_ERR, LOG_CRIT, LOG_ALERT, or LOG_EMERG
SYSLOG_IDENTITY psad;
SYSLOG_FACILITY LOG_LOCAL7;
SYSLOG_PRIORITY LOG_INFO;
### Port thresholds for logging and -S and -A output.
TOP_PORTS_LOG_THRESHOLD 500;
STATUS_PORTS_THRESHOLD 20;
### Signature thresholds for logging and -S and -A output.
TOP_SIGS_LOG_THRESHOLD 500;
STATUS_SIGS_THRESHOLD 50;
### Attackers thresholds for logging and -S and -A output.
TOP_IP_LOG_THRESHOLD 500;
STATUS_IP_THRESHOLD 25;
### Specify how often to log the TOP_* information (i.e. how many
### CHECK_INTERVAL iterations before the data is logged again).
TOP_SCANS_CTR_THRESHOLD 1;
### Send scan logs to dshield.org. This is disabled by default,
### but is a good idea to enable it (subject to your site security
### policy) since the DShield service helps to track the bad guys.
### For more information visit http://www.dshield.org
ENABLE_DSHIELD_ALERTS N;
### dshield.org alert email address; this should not be changed
### unless the guys at DShield have changed it.
DSHIELD_ALERT_EMAIL reports@dshield.org;
### Time interval (hours) to send email alerts to dshield.org.
### The default is 6 hours, and cannot be less than 1 hour or
### more than 24 hours.
DSHIELD_ALERT_INTERVAL 6; ### hours
### If you have a DShield user id you can set it here. The
### default is "0".
DSHIELD_USER_ID 0;
### If you want the outbound DShield email to appear as though it
### is coming from a particular user address then set it here.
DSHIELD_USER_EMAIL NONE;
### Threshold danger level for DShield data; a scan must reach this
### danger level before associated packets will be included in an
### alert to DShield. Note that zero is the default since this
### will allow DShield to apply its own logic to determine what
### constitutes a scan (_all_ iptables log messages will be included
### in DShield email alerts).
DSHIELD_DL_THRESHOLD 0;
### List of servers. Fwsnort supports the same variable resolution as
#### Snort.
HTTP_SERVERS $HOME_NET;
SMTP_SERVERS $HOME_NET;
DNS_SERVERS $HOME_NET;
SQL_SERVERS $HOME_NET;
TELNET_SERVERS $HOME_NET;
#### AOL AIM server nets
AIM_SERVERS [64.12.24.0/24, 64.12.25.0/24, 64.12.26.14/24, \
64.12.28.0/24, 64.12.29.0/24, 64.12.161.0/24, \
64.12.163.0/24, 205.188.5.0/24, 205.188.9.0/24];
### Configurable port numbers
HTTP_PORTS 80;
SHELLCODE_PORTS !80;
ORACLE_PORTS 1521;
### If this is enabled, then psad will die if a rule in the
### /etc/psad/signatures file contains an unsupported option (otherwise
### a syslog warning will be generated).
ENABLE_SNORT_SIG_STRICT Y;
### If "Y", enable automated IDS response (auto manages
### firewall rulesets).
ENABLE_AUTO_IDS N;
### Block all traffic from offending IP if danger
### level >= to this value
AUTO_IDS_DANGER_LEVEL 5;
### Set the auto-blocked timeout in seconds (the default
### is one hour).
AUTO_BLOCK_TIMEOUT 3600;
### Enable regex checking on log prefixes for active response
ENABLE_AUTO_IDS_REGEX N;
### Only block if the Netfilter log message matches the following regex
AUTO_BLOCK_REGEX ESTAB; ### from fwsnort logging prefixes
### Control whether "renew" auto-block emails get sent. This is disabled
### by default because lots of IPs could have been blocked, and psad
### should not generate a renew email for each of them.
ENABLE_RENEW_BLOCK_EMAILS N;
### By setting this variable to N, all auto-blocking emails can be
### suppressed.
ENABLE_AUTO_IDS_EMAILS Y;
### Enable iptables blocking (only gets enabled if
### ENABLE_AUTO_IDS is also set)
IPTABLES_BLOCK_METHOD Y;
### Specify chain names to which iptables blocking rules will be
### added with the IPT_AUTO_CHAIN{n} keyword. There is no limit on the
### number of IPT_AUTO_CHAIN{n} keywords; just increment the {n} number
### to add an additional IPT_AUTO_CHAIN requirement. The format for this
### variable is: <Target>,<Direction>,<Table>,<From_chain>,<Jump_rule_position>, \
### <To_chain>,<Rule_position>.
### "Target": Can be any legitimate Netfilter target, but should usually
### just be "DROP".
### "Direction": Can be "src", "dst", or "both", which correspond to the
### INPUT, OUTPUT, and FORWARD chains.
### "Table": Can be any Netfilter table, but the default is "filter".
### "From_chain": Is the chain from which packets will be jumped.
### "Jump_rule_position": Defines the position within the From_chain where
### the jump rule is added.
### "To_chain": Is the chain to which packets will be jumped. This is the
### main chain where psad rules are added.
### "Rule_position": Defines the position where rule are added within the
### To_chain.
###
### The following defaults make sense for most installations, but note
### it is possible to include blocking rules in, say, the "nat" table
### using this functionality as well. The following three lines provide
### usage examples:
#IPT_AUTO_CHAIN1 DROP, src, filter, INPUT, 1, PSAD_BLOCK_INPUT, 1;
#IPT_AUTO_CHAIN2 DROP, dst, filter, OUTPUT, 1, PSAD_BLOCK_OUTPUT, 1;
#IPT_AUTO_CHAIN3 DROP, both, filter, FORWARD, 1, PSAD_BLOCK_FORWARD, 1;
IPT_AUTO_CHAIN1 DROP, src, filter, INPUT, 1, PSAD_BLOCK_INPUT, 1;
IPT_AUTO_CHAIN2 DROP, dst, filter, OUTPUT, 1, PSAD_BLOCK_OUTPUT, 1;
IPT_AUTO_CHAIN3 DROP, both, filter, FORWARD, 1, PSAD_BLOCK_FORWARD, 1;
### Flush all existing rules in the psad chains at psad start time.
FLUSH_IPT_AT_INIT Y;
### Prerequisite check for existence of psad chains and jump rules
IPTABLES_PREREQ_CHECK 1;
### Enable tcp wrappers blocking (only gets enabled if
### ENABLE_AUTO_IDS is also set)
TCPWRAPPERS_BLOCK_METHOD N;
### Set the whois timeout
WHOIS_TIMEOUT 60; ### seconds
### Set the number of times an ip can be seen before another whois
### lookup is issued.
WHOIS_LOOKUP_THRESHOLD 20;
### Set the number of times an ip can be seen before another dns
### lookup is issued.
DNS_LOOKUP_THRESHOLD 20;
### Enable psad to run an external script or program (use at your
### own risk!)
ENABLE_EXT_SCRIPT_EXEC N;
### Define an external program to run after a scan is caught.
### Note that the scan source ip can be specified on the command
### line to the external program through the use of the "SRCIP"
### string (along with some appropriate switch for the program).
### Of course this is only useful if the external program knows
### what to do with this information.
### Example: EXTERNAL_SCRIPT /path/to/script --ip SRCIP -v;
EXTERNAL_SCRIPT /bin/true;
### Control execution of EXTERNAL_SCRIPT (only once per IP, or
### every time a scan is detected for an ip).
EXEC_EXT_SCRIPT_PER_ALERT N;
### Disk usage variables
DISK_CHECK_INTERVAL 300; ### seconds
### This can be set to 0 to disable disk checking altogether
DISK_MAX_PERCENTAGE 95;
### This can be set to 0 to have psad not place any limit on the
### number of times it will attempt to remove data from
### /var/log/psad/.
DISK_MAX_RM_RETRIES 10;
### Enable archiving of old scan directories at psad startup.
ENABLE_SCAN_ARCHIVE N;
### Truncate fwdata file at startup
TRUNCATE_FWDATA Y;
### Only archive scanning IP directories that have reached a danger
### level greater than or equal to this value. Archiving old
### scanning ip directories only takes place at psad startup.
MIN_ARCHIVE_DANGER_LEVEL 1;
### Email subject line config. Change these prefixes if you want
### psad to generate email alerts that say something other than
### the following.
MAIL_ALERT_PREFIX [psad-alert];
MAIL_STATUS_PREFIX [psad-status];
MAIL_ERROR_PREFIX [psad-error];
MAIL_FATAL_PREFIX [psad-fatal];
### URL for getting the latest psad signatures
SIG_UPDATE_URL http://www.cipherdyne.org/psad/signatures;
### These next two are psadwatchd vars
PSADWATCHD_CHECK_INTERVAL 5; ### seconds
PSADWATCHD_MAX_RETRIES 10;
### Directories
PSAD_DIR /var/log/psad;
PSAD_RUN_DIR /var/run/psad;
PSAD_FIFO_DIR /var/lib/psad;
PSAD_LIBS_DIR /usr/lib/psad;
PSAD_CONF_DIR /etc/psad;
PSAD_ERR_DIR $PSAD_DIR/errs;
CONF_ARCHIVE_DIR $PSAD_CONF_DIR/archive;
SCAN_DATA_ARCHIVE_DIR $PSAD_DIR/scan_archive;
ANALYSIS_MODE_DIR $PSAD_DIR/ipt_analysis;
SNORT_RULES_DIR $PSAD_CONF_DIR/snort_rules;
### Files
FW_DATA_FILE $PSAD_DIR/fwdata;
ULOG_DATA_FILE $PSAD_DIR/ulogd.log;
FW_CHECK_FILE $PSAD_DIR/fw_check;
DSHIELD_EMAIL_FILE $PSAD_DIR/dshield.email;
SIGS_FILE $PSAD_CONF_DIR/signatures;
ICMP_TYPES_FILE $PSAD_CONF_DIR/icmp_types;
AUTO_DL_FILE $PSAD_CONF_DIR/auto_dl;
SNORT_RULE_DL_FILE $PSAD_CONF_DIR/snort_rule_dl;
POSF_FILE $PSAD_CONF_DIR/posf;
P0F_FILE $PSAD_CONF_DIR/pf.os;
IP_OPTS_FILE $PSAD_CONF_DIR/ip_options;
PSAD_FIFO_FILE $PSAD_FIFO_DIR/psadfifo;
ETC_HOSTS_DENY_FILE /etc/hosts.deny;
ETC_SYSLOG_CONF /etc/syslog.conf;
ETC_SYSLOGNG_CONF /etc/syslog-ng/syslog-ng.conf;
ETC_METALOG_CONF /etc/metalog/metalog.conf;
STATUS_OUTPUT_FILE $PSAD_DIR/status.out;
ANALYSIS_OUTPUT_FILE $PSAD_DIR/analysis.out;
INSTALL_LOG_FILE $PSAD_DIR/install.log;
### PID files
PSAD_PID_FILE $PSAD_RUN_DIR/psad.pid;
PSAD_CMDLINE_FILE $PSAD_RUN_DIR/psad.cmd;
KMSGSD_PID_FILE $PSAD_RUN_DIR/kmsgsd.pid;
PSADWATCHD_PID_FILE $PSAD_RUN_DIR/psadwatchd.pid;
### List of ips that have been auto blocked by iptables
### or tcpwrappers (the auto blocking feature is disabled by
### default, see the psad man page and the ENABLE_AUTO_IDS
### variable).
AUTO_BLOCK_IPT_FILE $PSAD_DIR/auto_blocked_iptables;
AUTO_BLOCK_TCPWR_FILE $PSAD_DIR/auto_blocked_tcpwr;
### File used internally by psad to add Netfilter blocking
### rules to a running psad process
AUTO_IPT_SOCK $PSAD_RUN_DIR/auto_ipt.sock;
FW_ERROR_LOG $PSAD_ERR_DIR/fwerrorlog;
PRINT_SCAN_HASH $PSAD_DIR/scan_hash;
### /proc interface for controlling ip forwarding
PROC_FORWARD_FILE /proc/sys/net/ipv4/ip_forward;
### Packet counters for tcp, udp, and icmp protocols
PACKET_COUNTER_FILE $PSAD_DIR/packet_ctr;
### Top scanned ports
TOP_SCANNED_PORTS_FILE $PSAD_DIR/top_ports;
### Top signature matches
TOP_SIGS_FILE $PSAD_DIR/top_sigs;
### Top attackers
TOP_ATTACKERS_FILE $PSAD_DIR/top_attackers;
### Counter file for Dshield alerts
DSHIELD_COUNTER_FILE $PSAD_DIR/dshield_ctr;
### Counter file for iptables prefixes
IPT_PREFIX_COUNTER_FILE $PSAD_DIR/ipt_prefix_ctr;
### iptables command output and error collection files; these are
### used by IPTables::ChainMgr
IPT_OUTPUT_FILE $PSAD_DIR/psad.iptout;
IPT_ERROR_FILE $PSAD_DIR/psad.ipterr;
### system binaries
iptablesCmd /sbin/iptables;
shCmd /bin/sh;
wgetCmd /usr/bin/wget;
gzipCmd /bin/gzip;
mknodCmd /bin/mknod;
psCmd /bin/ps;
mailCmd /bin/mail;
sendmailCmd /usr/sbin/sendmail;
ifconfigCmd /sbin/ifconfig;
killallCmd /usr/bin/killall;
netstatCmd /bin/netstat;
unameCmd /bin/uname;
whoisCmd /usr/bin/whois_psad;
dfCmd /bin/df;
fwcheck_psadCmd /usr/sbin/fwcheck_psad;
psadwatchdCmd /usr/sbin/psadwatchd;
kmsgsdCmd /usr/sbin/kmsgsd;
psadCmd /usr/sbin/psad;
