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Home » Featured, Networking

Automatically Block Frequent Visitors

Submitted by on December 9, 2019 – 9:45 pm

I had a few similar scripts floating around this site, but this one is a bit more all-inclusive and better organized. The script will analyze your firewall/whatever access log and block particularly active visitors.

I added some extensive (for me, at least) comments to the script, but here’s some explanation anyway. What the script does:

  1. Checks specified log files for specific lines matching the regex. The default syntax is for a typical firewall log showing src and dst:port and whether the connection was allowed or dropped.
  2. From there the script will grab the lines matching the destination IPs and ports that you specified. You can either specify the destination IP or have it automatically set to your external Internet IP. This may be useful if you don’t have a static IP. You can specify multiple ports, or the script will get a list by running nmap against your server’s external IP (or whatever IP you specified).
  3. From the results, the script will exclude private networks. This is something you may need to adjust, if your destination IP is on the private network.
  4. The next step is to exclude any IPs listed in your /etc/hosts.allow. You can easily change this to any other IP whitelist file, or just enter IPs manually into the script.
  5. Extract unique source IPs and analyze their frequency. Select those that exceed the threshold. This threshold is an entirely arbitrary value that you must deduce based on how popular your server is.
  6. Try to determine location and owner of the source IP and filter out any that match entries in your second whitelist. This second whitelist may contain information like country, state, city, name of the organization – basically anything that can be generated by the geoiplookup command. This allows you to exclude certain organizations and geographical locations without having to specify a huge number of network ranges.
  7. The offending IPs will be blacklisted. There is an option to blacklist them for a period from one to whatever number of days.

If you’re not interested in having your Web site, FTP server, etc. downloaded over and over again by various “search engines” and “security researchers”, this script can automatically hamper their similarly automated efforts.

The script can be fairly easily modified to use the org_whitelist variable for blacklisting, instead of whitelisting. This way you can drop the threshold down to a minimum and blacklist based not on the number of hits, but on a specific geographic location or the organization name.

The script is below and you can also download it from my GitHub repo here.

#                                      |
#                                  ___/"\___
#                          __________/ o \__________
#                            (I) (G) \___/ (O) (R)
#                                   Igor Os
#                                 2019-09-19
# ----------------------------------------------------------------------------
# Script description
# The script will identify this system's external (Internet) IP address and
# open network ports. The script will then analyze firewall log entries for
# access records to this IP address and ports. If the number of succesfull
# connections from any single source exceeds the set threshold, the script
# will block the source IP via local firewall. An exception will be made
# for any IPs listed in /etc/hosts.allow and for private networks.
# Documentation URL: https://
# ----------------------------------------------------------------------------
# 2019-09-19  igor  wrote this script
# ----------------------------------------------------------------------------
function func_configure() {
# Just some basic config stuff
this_script=$(basename "$(test -L "$0" && readlink "$0" || echo "$0")")
this_script_full="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/$(basename "${BASH_SOURCE[0]}")"
this_host=$(hostname | awk -F'.' '{print $1}')
this_time=$(date +'%Y-%m-%d %H:%M:%S')
mail_subject="Alert from ${this_host}:${this_script_full} at ${this_time}"
# When blacklisting IPs, a comment will be added to the iptables rule. The comment will
# consist of an epoch timestamp set ${jailtime} days in the future. This gives you an
# opportunity to blacklist IPs temporarily. If you don't require this feature, set this
# variable to 0
# Either specify the target IP or have it set to your external Internet IP. This may
# be useful if you don't have a static IP.
#target_ips="$(wget -O - -q ; echo)"
# Specify target ports or have them set dynamically by running nmap against your
# primary IP set in the previous step.
#target_ports="$(nmap $target_ips 2>/dev/null | grep -oP "(?<=^)[0-9]{1,5}(?=\/)" | xargs | sed 's/ /|/g')"
# The threshold in this case is entirely arbitrary. You'd have to set it according to how
# popular your server is and what you would consider 'too many' hits.
# This is the log file that contains your firewall records. You can specify multiple log files
# by providing absolute paths separated with spaces. You can also use asterisk at the end of
# the filename to include any rotated/compressed logs (i.e. /var/log/messages* will include
# /var/log/messages.0, /var/log/messages.1.gz, etc
# Target IP and at least one target port is required. If none were specified and none
# could be determined automatically, the script cannot continue.
if [ -z "${target_ips}" ] || [ -z "${target_ports}" ]
exit 1
# Just to let you know which logs and for what records the script is checking
echo "Checking access records for ${target_ips}:${target_ports} in ${logfiles}"
i=0; echo "${i}" > ${tmpfile}
k=0; echo "${k}" > ${tmpfile3}
# Add to whitelist whatever IPs you have listed in /etc/hosts.allow
whitelist="$(grep -oE "([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})" /etc/hosts.allow 2>/dev/null | \
sort -V | uniq | xargs | sed 's/ /|/g')"
if [ -z "${whitelist}" ]
# If your /etc/hosts.allow is empty or doesn't exist, then at least whitelist
# the local primary IP and your external Internet IP
whitelist="$(/sbin/ifconfig | sed -rn 's/;s/.*inet (addr:)?(([0-9]*\.){3}[0-9]*).*/\2/p' | head -1)|$(wget -O - -q ;echo)"
# Here you can enter names of organizations (or whatever other strings) that may appear
# in the output of the geoiplookup command. This allows you to whitelist IPs belonging
# to a particular organization or geographic location
org_whitelist="Delaware, Wilmington|Google"
function func_log_scan() {
# The first line below you may need to adjust to matche specific format of your firewall log
# The second line greps for the source IP address. You may need to make some changes here as well
# The third line exclude private subnets (your local company or home networks)
# The fourth line excludes any IP that is whitelisted
# The fifth line extracts unique IPs, counts the number of hits, and selects those that exceeded the threshold
for src_ip in $(zgrep -hE "dst=\"(${target_ips}):(${target_ports})\"" ${logfiles} 2>/dev/null | grep -v "DROP" |\
grep -oP "(?<=src=\")([0-9]{1,3}\.){3}([0-9]{1,3})(?=:[0-9])" | \
grep -vE "(^0\.)|(^127\.)|(^10\.)|(^172\.1[6-9]\.)|(^172\.2[0-9]\.)|(^172\.3[0-1]\.)|(^192\.168\.)" | \
grep -vE "${whitelist}" | \
sort -V | uniq -c | sort -k1rn | awk -v t=$threshold '{if($1>t)print$2}')
# Check if the selected IP may already be in your iptables either explicitly,
# or as part of a subnet
if [ $(/sbin/iptables -S | grepcidr -c "${src_ip}/32") -eq 0 ]
# Try to get owner/location information for the IP address
src_info="$(geoiplookup ${src_ip} 2>/dev/null | grep -v 'not found' | awk -F: '{$1=""; print $0}' | sed 's/\//_/g' | xargs 2>/dev/null)"
if [ -z "${src_info}" ]
src_info="unknown source"
# Check the org_whitelist and block the IP and add a record to the system log.
# These entries can be used to revert any unintended blocks.
if [ $(echo "${src_info}" | grep -cE "${org_whitelist}") -eq 0 ]
echo "Blocking ${src_ip} after more than ${threshold} hits on ${target_ips}:${target_ports} from ${src_info}" | logger -t "${this_script}"
if [ ${jailtime} -gt 0 ]
/sbin/iptables -A INPUT -m comment --comment "$(date -d"now + ${jailtime} days" +'%s')" -s "${src_ip}" -j DROP
/sbin/iptables -A INPUT -s "${src_ip}" -j DROP
(( i = i + 1 ))
echo "${i}" > ${tmpfile}
function func_unblock() {
if [ ${jailtime} -gt 0 ]
/sbin/iptables -S | grep -E 'comment.*"[0-9]{10,}"' | while read l
if [ $(echo ${l} | grep -oE '[0-9]{10,}') -lt $(date +'%s') ]
echo "${this_script} is dropping expired firewall block: ${l}"
j="$(echo ${l} | sed 's/\-A/\-D/g')"
/sbin/iptables $(eval echo $j)
(( k = k + 1 ))
echo "${k}" > ${tmpfile3}
function func_iptables_save() {
# If iptables configuration was modified, removes any duplicates and save it.
# After saving, reload iptables service and send an email to the administrator.
if [ $(cat ${tmpfile}) -gt 0 ] || [ $(cat ${tmpfile3}) -gt 0 ]
/sbin/service iptables save 2>/dev/null 1>$2
/sbin/iptables-save | awk '/^COMMIT$/ { delete x; }; !x[$0]++' > ${tmpfile2}
/sbin/iptables -F
/sbin/iptables-restore < ${tmpfile2}
/sbin/service iptables save
/sbin/service iptables reload
grep "${this_script}" /var/log/messages | tail -$(cat ${tmpfile}) |\
mailx -r "${mail_from}" -s "${mail_subject}" "${mail_to}"
function func_cleanup() {
# Clean up any lingering temp files
/bin/rm -f ${tmpfile} ${tmpfile2} ${tmpfile3} 2>/dev/null
# ----------------------------------------------------------------------------
# \(^_^)/                                      __|__
#                                     __|__ *---o0o---*
#                            __|__ *---o0o---*
#                         *---o0o---*
# ----------------------------------------------------------------------------


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