who is trying to brute-force my password?
I was looking into my log files on my server and I found the following lines in: /var/log/.auth.log.1:
pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruse r= rhost=218.87.109.156 user=root
Failed password for root from 218.87.109.156 port 7612 ssh2
message repeated 5 times: [ Failed password for root from 218.87.109.156 port 7 612 ssh2]
error: maximum authentication attempts exceeded for root from 218.87.109.156 po rt 7612 ssh2 [preauth]
Disconnecting: Too many authentication failures [preauth]
PAM 5 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost= 218.87.109.156 user=root
PAM service(sshd) ignoring max retries; 6 > 3
pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruse r= rhost=218.87.109.156 user=root
Failed password for root from 218.87.109.156 port 50092 ssh2
message repeated 5 times: [ Failed password for root from 218.87.109.156 port 5 0092 ssh2]
Failed password for invalid user service from 188.187.119.158 port 52722 ssh2
pam_unix(sshd:auth): check pass; user unknown
Failed password for root from 113.195.145.79 port 6500 ssh2
Received disconnect from 121.18.238.39 port 58070:11: [preauth]
Failed password for root from 121.18.238.119 port 57538 ssh2
Failed password for root from 121.18.238.39 port 57268 ssh2
Failed password for root from 121.18.238.106 port 34360 ssh2
Disconnected from 92.222.216.31 port 58960 [preauth]
Invalid user truman from 92.222.216.31
Received disconnect from 92.222.216.31 port 33922:11: Normal Shutdown, Thank you for playing [preauth]
input_userauth_request: invalid user truman [preauth]
And it keeps going on like this for thousands of lines!
And also somewhere I have:
Nov 30 13:17:01 Aran CRON[6038]: pam_unix(cron:session): session opened for user root by (uid=0)
What does CRON mean in here? so can somebody please explain to me what are these logs? Am I in danger? what should I do to get myself more secure?
All those attempted logins are for the root user so it looks like just basic brute-force attempts via SSH.
It's entirely normal for a public-facing server to have lots of SSH brute-force attempts a day. It's a fact of life. You can start reporting them to the ISP who owns the IP address, but it's whack-a-mole and you're not going to make a big difference. They're using compromised computers all over the internet and/or hosting accounts they signed up for under false details.
What would make a difference is if everyone decided to disable root login over SSH, and/or require key-based login for root (or for everyone). As long as you've done one of these the brute-force attempts will basically be ineffective. But because enough people still leave plain root login enabled, and have a guessable password on it, these attacks continue.
Another thing that some people recommend is switching your SSH daemon to a non-standard port number. This doesn't really give a significant security benefit but it will cut down on the number of attempts reaching your logfiles.
As for your second question, this is just Cron running, which is the program that runs scheduled tasks. All systems have a bunch of scheduled tasks configured by default by the system. Since cron can run different tasks as different users it uses pam_unix to handle starting a user session, even when root, so that's why it appears in that log.
This answer doesn't really answer who is trying to log into your host, but it can give you an idea of where the person is coming from. Also help in preventing hackers from even getting to your host.
If you're going to use passwords for logging in through ssh, you should take some precautions as to people trying to hack into your system. For my personal use I like to use fail2ban and then I wrote my own script that uses iptables and ipset. The latter part I use for complete blocking of country IPs from coming in to my host on port 22. I have also installed geoiplookup as a way to see where the IP is coming from to decide if I want to block the country or not. The script I have below obtains the sets of IPs from ipdeny.com. It has drastically reduced the amount of attempts on my host since I leave port 22 open most of the time.
Installing fail2ban:
sudo apt install fail2ban
Usually with fail2ban the default settings are OK. If you want to change them make sure to copy /etc/fail2ban/jail.conf as /etc/fail2ban/jail.local and make the modifications to the jail.local file you have created. You can also see failed attempts in the /var/log/fail2ban.log file.
Installing geoiplookup:
sudo apt install geoip-bin
Then you can see where the IP addresses are coming from.
~$ geoiplookup 218.87.109.156
GeoIP Country Edition: CN, China
The country blocking script that I created.
A required application for the country block is ipset. This application allows iptables to use a block of IPs instead of showing every individual IP address when you check the status of iptables.
sudo apt install ipset
I am certain that there is a lot that can be cleaned up. I put mine in my home folder in a subfolder of scripts and called it country_block.bsh. Since the script makes changes to iptables it has to be called from sudo. I did add the check into the script. I have made some recent changes to the script to REJECT the packets instead of dropping so the connection is instantly disconnected.
#!/bin/bash
function custom(){
echo "Removing CUSTOM_IP set..."
prts=$(iptables -nvL INPUT | awk '/CUSTOM_IP/ {print $15}')
iptables -D INPUT -p tcp -m set --match-set CUSTOM_IP src -m multiport --dport ${prts} -j REJECT 2>/dev/null
ipset destroy CUSTOM_IP
ipset -N CUSTOM_IP hash:net
echo "Creating CUSTOM_IP set..."
for i in $(cat custom.zone); do ipset -A CUSTOM_IP $i; done
echo "Creating rules for CUSTOM_IP set..."
iptables -A INPUT -p tcp -m set --match-set CUSTOM_IP src -m multiport --dports ${ports} -j REJECT
}
function tablecheck(){
iptables -S INPUT | grep -v ACCEPT
}
# Check for ipset
which ipset >/dev/null
case $? in
1) echo "ipset not found on system. Please install ipset application."
echo "This is normally installed by sudo apt install ipset"
exit 1;;
0);;
esac
# Check for root
if [ "$EUID" -ne 0 ]; then
echo "Please run this script as root"
exit 1
fi
# Set ports
#ports=21,22,10000
ports=22,10000
# Check for country codes, if none, print list.
if [[ $@ == "" ]]; then
curl https://www.ipdeny.com/ipblocks/ 2>/dev/null | grep "<td>" | awk -F'<p>' '{print $2}' | awk -F'[' '{print $1}' | grep -v -e '^$'
echo "Choose any of the countries by typing in the two letter code between the ( )."
exit
fi
if [[ $1 == "custom" ]]; then
if [ ! -f custom.zone ]; then
echo "Missing custom.zone file. Please create custom.zone file with IP addresses for blocking."
exit
fi
custom
tablecheck
exit
fi
#Set ISO to country code(s).
ISO=$@
#Start Loop for country IP blocks and creating IPTABLES chain(s).
for c in $ISO; do
#Convert to lowercase. If already lowercase, ignored.
c=$(echo $c | awk '{print tolower($0)}')
#Match code to country name
country=$(curl https://www.ipdeny.com/ipblocks/ 2>/dev/null | grep \($(echo $c | awk '{print toupper($0)}')\) | awk -F'<p>' '{print $2}' | awk -F'(' '{print $1}' | sed 's/ //g' | sed 's/,//g')
# Truncate to 31 characters if too long.
country=${country:0:31}
echo "Got country $country..."
echo "Removing Existing Rule for $country (if any)..."
prts=$(iptables -nvL INPUT | grep "$country" | awk '{print $15}')
iptables -D INPUT -p tcp -m set --match-set "$country" src -m multiport --dport ${prts} -j REJECT 2>/dev/null
ipset destroy $country
ipset -N $country hash:net
rm $c.zone 2>/dev/null
echo "Downloading IP block for $country..."
wget -P . https://www.ipdeny.com/ipblocks/data/aggregated/$c-aggregated.zone 2>/dev/null
echo "Checking for invalid IP ranges in $country zone..."
for i in $(seq 1 7); do grep "/$i$" $c-aggregated.zone; if [[ $? == "0" ]]; then sed -i "s/\/${i}$/\/24/" $c-aggregated.zone; echo "Fixed..."; fi; done
echo "Creating iptable block for $country..."
for i in $(cat $c-aggregated.zone); do ipset -A "$country" $i; done
echo "Adding rule to firewall..."
iptables -A INPUT -p tcp -m set --match-set "$country" src -m multiport --dports ${ports} -j REJECT
echo "Added Firewall Rule for $country"
rm $c-aggregated.zone 2>/dev/null
done
if [[ $# == "1" || $1 -ne "custom" ]]; then
tablecheck
else
if [ ! -f custom.zone ]; then
echo "Missing custom.zone file. Please create custom.zone file with IP addresses for blocking."
tablecheck
exit
fi
custom
fi
if [[ $# -ne "1" ]]; then
tablecheck
fi
#iptables -S INPUT | grep -v ACCEPT
Make sure to make the script executable (chmod +x country_block.bsh). You can then create a custom.zone in the same folder as the country_block.bsh file with just IPs that might be trying over and over again to hack your system. Add them with a /32 at the end of the IP address like 256.99.265.106/32. After you add your own custom IPs, you can reload them in simply by running:
sudo ./country_block.bsh custom
Be careful not to block your own country or your own public IP.
Also be careful not to block any other ports that are not open. If you block port 80, there is a chance that if you visit a website from that country it will not load because it cannot return to your system on port 80.
Then I created another script in my home folder called cb_update.bsh that contains all the countries I want to block:
#!/bin/bash
cd /home/terrance/scripts/
./country_block.bsh cn ru nl de dk fr id ie it kr sg tw vn br ua pt il gb jp pk ar co fi in
If you want to block all countries except for your own change the above line to the following and make sure to add your country into the " " at the end of the line to remove your country from the list:
./country_block.bsh $(./country_block.bsh | awk -F '[()]' '{print $(NF-1)}' | grep -v "US")
Then I added the following lines to my /etc/crontab file. It covers every time my system reboots and it updates the list at 01:05 in the morning.
$ cat /etc/crontab
@reboot root /bin/bash -c 'sleep 20 && /home/terrance/cb_update.bsh'
01 05 * * * root /home/terrance/cb_update.bsh
If you run the script by itself, it will give you the country codes:
terrance@terrance-ubuntu:~/scripts$ sudo ./country_block.bsh
AFGHANISTAN (AF)
LAND ISLANDS (AX)
ALBANIA (AL)
ALGERIA (DZ)
AMERICAN SAMOA (AS)
ANDORRA (AD)
ANGOLA (AO)
ANGUILLA (AI)
ANTIGUA AND BARBUDA (AG)
ARGENTINA (AR)
ARMENIA (AM)
ARUBA (AW)
AUSTRALIA (AU)
AUSTRIA (AT)
AZERBAIJAN (AZ)
BAHAMAS (BS)
BAHRAIN (BH)
BANGLADESH (BD)
BARBADOS (BB)
BELARUS (BY)
BELGIUM (BE)
BELIZE (BZ)
BENIN (BJ)
BERMUDA (BM)
BHUTAN (BT)
BOLIVIA (BO)
BOSNIA AND HERZEGOVINA (BA)
BOTSWANA (BW)
BRAZIL (BR)
BRITISH INDIAN OCEAN TERRITORY (IO)
BRUNEI DARUSSALAM (BN)
BULGARIA (BG)
BURKINA FASO (BF)
BURUNDI (BI)
CAMBODIA (KH)
CAMEROON (CM)
CANADA (CA)
CAPE VERDE (CV)
CAYMAN ISLANDS (KY)
CENTRAL AFRICAN REPUBLIC (CF)
CHAD (TD)
CHILE (CL)
CHINA (CN)
COLOMBIA (CO)
COMOROS (KM)
CONGO (CG)
CONGO, THE DEMOCRATIC REPUBLIC OF THE (CD)
COOK ISLANDS (CK)
COSTA RICA (CR)
COTE D'IVOIRE (CI)
CROATIA (HR)
CUBA (CU)
CYPRUS (CY)
CZECH REPUBLIC (CZ)
DENMARK (DK)
DJIBOUTI (DJ)
DOMINICA (DM)
DOMINICAN REPUBLIC (DO)
ECUADOR (EC)
EGYPT (EG)
EL SALVADOR (SV)
EQUATORIAL GUINEA (GQ)
ERITREA (ER)
ESTONIA (EE)
ETHIOPIA (ET)
FAROE ISLANDS (FO)
FIJI (FJ)
FINLAND (FI)
FRANCE (FR)
FRENCH GUIANA (GF)
FRENCH POLYNESIA (PF)
GABON (GA)
GAMBIA (GM)
GEORGIA (GE)
GERMANY (DE)
GHANA (GH)
GIBRALTAR (GI)
GREECE (GR)
GREENLAND (GL)
GRENADA (GD)
GUADELOUPE (GP)
GUAM (GU)
GUATEMALA (GT)
GUINEA (GN)
GUINEA-BISSAU (GW)
GUYANA (GY)
HAITI (HT)
HOLY SEE (VATICAN CITY STATE) (VA)
HONDURAS (HN)
HONG KONG (HK)
HUNGARY (HU)
ICELAND (IS)
INDIA (IN)
INDONESIA (ID)
IRAN, ISLAMIC REPUBLIC OF (IR)
IRAQ (IQ)
IRELAND (IE)
ISLE OF MAN (IM)
ISRAEL (IL)
ITALY (IT)
JAMAICA (JM)
JAPAN (JP)
JERSEY (JE)
JORDAN (JO)
KAZAKHSTAN (KZ)
KENYA (KE)
KIRIBATI (KI)
KOREA, DEMOCRATIC PEOPLE'S REPUBLIC OF (KP)
KOREA, REPUBLIC OF (KR)
KUWAIT (KW)
KYRGYZSTAN (KG)
LAO PEOPLE'S DEMOCRATIC REPUBLIC (LA)
LATVIA (LV)
LEBANON (LB)
LESOTHO (LS)
LIBERIA (LR)
LIBYAN ARAB JAMAHIRIYA (LY)
LIECHTENSTEIN (LI)
LITHUANIA (LT)
LUXEMBOURG (LU)
MACAO (MO)
MACEDONIA, THE FORMER YUGOSLAV REPUBLIC OF (MK)
MADAGASCAR (MG)
MALAWI (MW)
MALAYSIA (MY)
MALDIVES (MV)
MALI (ML)
MALTA (MT)
MARSHALL ISLANDS (MH)
MARTINIQUE (MQ)
MAURITANIA (MR)
MAURITIUS (MU)
MAYOTTE (YT)
MEXICO (MX)
MICRONESIA, FEDERATED STATES OF (FM)
MOLDOVA, REPUBLIC OF (MD)
MONACO (MC)
MONGOLIA (MN)
MONTENEGRO (ME)
MONTSERRAT (MS)
MOROCCO (MA)
MOZAMBIQUE (MZ)
MYANMAR (MM)
NAMIBIA (NA)
NAURU (NR)
NEPAL (NP)
NETHERLANDS (NL)
NEW CALEDONIA (NC)
NEW ZEALAND (NZ)
NICARAGUA (NI)
NIGER (NE)
NIGERIA (NG)
NIUE (NU)
NORFOLK ISLAND (NF)
NORTHERN MARIANA ISLANDS (MP)
NORWAY (NO)
OMAN (OM)
PAKISTAN (PK)
PALAU (PW)
PALESTINIAN TERRITORY, OCCUPIED (PS)
PANAMA (PA)
PAPUA NEW GUINEA (PG)
PARAGUAY (PY)
PERU (PE)
PHILIPPINES (PH)
POLAND (PL)
PORTUGAL (PT)
PUERTO RICO (PR)
QATAR (QA)
REUNION (RE)
ROMANIA (RO)
RUSSIAN FEDERATION (RU)
RWANDA (RW)
SAINT KITTS AND NEVIS (KN)
SAINT LUCIA (LC)
SAINT PIERRE AND MIQUELON (PM)
SAINT VINCENT AND THE GRENADINES (VC)
SAMOA (WS)
SAN MARINO (SM)
SAO TOME AND PRINCIPE (ST)
SAUDI ARABIA (SA)
SENEGAL (SN)
SERBIA (RS)
SEYCHELLES (SC)
SIERRA LEONE (SL)
SINGAPORE (SG)
SLOVAKIA (SK)
SLOVENIA (SI)
SOLOMON ISLANDS (SB)
SOMALIA (SO)
SOUTH AFRICA (ZA)
SPAIN (ES)
SRI LANKA (LK)
SUDAN (SD)
SURINAME (SR)
SWAZILAND (SZ)
SWEDEN (SE)
SWITZERLAND (CH)
SYRIAN ARAB REPUBLIC (SY)
TAIWAN (TW)
TAJIKISTAN (TJ)
TANZANIA, UNITED REPUBLIC OF (TZ)
THAILAND (TH)
TIMOR-LESTE (TL)
TOGO (TG)
TOKELAU (TK)
TONGA (TO)
TRINIDAD AND TOBAGO (TT)
TUNISIA (TN)
TURKEY (TR)
TURKMENISTAN (TM)
TURKS AND CAICOS ISLANDS (TC)
TUVALU (TV)
UGANDA (UG)
UKRAINE (UA)
UNITED ARAB EMIRATES (AE)
UNITED KINGDOM (GB)
UNITED STATES (US)
UNITED STATES MINOR OUTLYING ISLANDS (UM)
URUGUAY (UY)
UZBEKISTAN (UZ)
VANUATU (VU)
VENEZUELA (VE)
VIET NAM (VN)
VIRGIN ISLANDS, BRITISH (VG)
VIRGIN ISLANDS, U.S. (VI)
WALLIS AND FUTUNA (WF)
YEMEN (YE)
ZAMBIA (ZM)
ZIMBABWE (ZW)
Choose any of the countries by typing in the two letter code between the ( ).
You can then check at anytime the hits that might be happening to your system.
$ sudo iptables -nvL INPUT
Chain INPUT (policy ACCEPT 9523 packets, 3125K bytes)
pkts bytes target prot opt in out source destination
0 0 ACCEPT udp -- virbr0 * 0.0.0.0/0 0.0.0.0/0 udp dpt:53
0 0 ACCEPT tcp -- virbr0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:53
0 0 ACCEPT udp -- virbr0 * 0.0.0.0/0 0.0.0.0/0 udp dpt:67
0 0 ACCEPT tcp -- virbr0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:67
0 0 f2b-proftpd tcp -- * * 0.0.0.0/0 0.0.0.0/0 multiport dports 21,20,990,989
2847 170K f2b-sshd tcp -- * * 0.0.0.0/0 0.0.0.0/0 multiport dports 22
12 548 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set CHINA src multiport dports 22,10000
4 176 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set RUSSIANFEDERATION src multiport dports 22,10000
1 44 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set NETHERLANDS src multiport dports 22,10000
2 88 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set GERMANY src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set DENMARK src multiport dports 22,10000
157 8156 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set FRANCE src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set INDONESIA src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set IRELAND src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set ITALY src multiport dports 22,10000
4 180 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set KOREAREPUBLICOF src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set SINGAPORE src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set TAIWAN src multiport dports 22,10000
947 48804 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set VIETNAM src multiport dports 22,10000
2 92 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set BRAZIL src multiport dports 22,10000
6 264 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set UKRAINE src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set PORTUGAL src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set ISRAEL src multiport dports 22,10000
3 180 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set UNITEDKINGDOM src multiport dports 22,10000
1 44 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set JAPAN src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set PAKISTAN src multiport dports 22,10000
2 88 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set ARGENTINA src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set COLOMBIA src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set FINLAND src multiport dports 22,10000
4 188 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set INDIA src multiport dports 22,10000
0 0 REJECT tcp -- * * 0.0.0.0/0 0.0.0.0/0 match-set CUSTOM_IP src multiport dports 22,10000
Hope this helps!