General Information

ClamAV is “an open source antivirus engine for detecting trojans, viruses, malware and other malicious threats.”

• Official Site: http://www.clamav.net/index.html
• Virus Database Mail List Archives: http://www.gossamer-threads.com/lists/clamav/virusdb/
• User Mailing List Archives: http://www.gossamer-threads.com/lists/clamav/users/

Checklist

• Distro(s): Enterprise Linux 6
• Repo: EPEL

Installing ClamAV.

• Add the EPEL repo.
• Install ClamAV Scanner and Auto Updater (Freshclam)
  • EL 6

    yum install clamav

  • EL 7

    yum install clamav clamav-update

• Install ClamAV's Scanning Daemon (clamd)
  • EL 6

    yum install clamd

  • EL 7

    yum install clamav-scanner-systemd

Configuring ClamAV.

Virus definition updater for ClamAV.

• Config: /etc/freshclam.conf
• Daily Cron: /etc/cron.daily/freshclam

/etc/freshclam.conf - Ensure Database Mirrors are correct

DatabaseMirror db.us.clamav.net
DatabaseMirror db.local.clamav.net

If you have a Squid proxy

HTTPProxyServer myserverhostname
HTTPProxyPort 3128

Run manual virus updates

freshclam -v

Using ClamAV.

ClamAV software runs as non-privileged user(s).

EL 6

• Freshclam runs as: clam
• Clamd runs as: clam

EL 7

• Freshclam runs as: clamupdate
• Clamd runs as: clamscan

Freshclam is NOT a service. It is run via a daily cron script.

Clamd (the scanning daemon) is run as a service. It does not scan anything by itself unless “on access scanning” is enabled.

• To scan certain directories regularly, either enable on access scanning, or create a cron that runs clamdscan against directories.

Enable On Boot

Service is enabled on boot

• EL6

  chkconfig clamd on

• EL7

  systemctl enable clamd@scan

Service Status

• EL6

  service clamd status

• EL7

  systemctl status clamd@scan

Service Start

• EL6

  service clamd start

• EL7

  systemctl start clamd@scan

Service Stop

• EL6

  service clamd stop

• EL7

  systemctl stop clamd@scan

Log files are located:

• Freshclam
  • EL 6: /var/log/clamav/freshclam.log
  • EL 7: /var/log/freshclam.log
• Clamd
  • EL 6: /var/log/clamav/clamd.log
  • EL 7: /var/log/clamd.scan

• Freshclam (Virus Definitions Database Updater)
  • Application: freshclam (/usr/bin/freshclam)
  • Configuration: /etc/freshclam.conf
  • Auto Update job: /etc/cron.daily/freshclam

• Scanning Daemon (clamd)
  • Configuration:
    • EL 6: /etc/clamd.conf
    • EL 7: /etc/clamd.d/scan.conf

• ClamAV Databases: /var/lib/clamav
  • bytecode.cvd - detailed bytecode signatures database for virus detection
  • daily.cld - daily definition database from deltas build throughout the day
  • main.cvd - main database of definitions

Clamscan is the utility that scans files and directories for viruses.

Scan a single file

clamscan myfile

Scan the current working directory

clamscan

Scan a directory recursively

clamscan -r /home/rjones

Scan a stream

cat myfile | clamscan -

Clamscan return codes

• 0 ⇒ no virus found
• 1 ⇒ virus(es) found
• 2 ⇒ Some error(s) occured

The clamd service allows for faster scanning of directories and files.

One off system scan of /home using clamdscan

/usr/bin/time nice clamdscan --fdpass --log=/root/clamdscan-report-$(date +%Y%m%d) /home

• /usr/bin/time ⇒ Times how long the scan takes
• nice ⇒ Less CPU priority for the scan
• –fdpass ⇒ Pass file descriptor permissions to clamd (allows for a faster scan when clamd is running as a different user)
• –log=/root/clamdscan-report-$(date +%Y%m%d) ⇒ Create log file here

To scan systems regularly, use clamdscan and either

• Enable on access scanning
• Create a cron to launch clamdscan

Example: Enable on access scanning

• → Show this example

Example: Create a cron to launch clamdscan

• → Show this example

Whitelisting files/signatures allows for ClamAV to ignore them during scans.

To whitelist a file:

• Generate a md5 signature for the file and append it to the file whitelist

  sigtool --md5 /data/testfile >> /var/lib/clamav/whitelist-files.fp

  • The entry will look like this

    cat /var/lib/clamav/whitelist-files.fp
     
    d41d8cd98f00b204e9800998ecf8427e:0:testfile

    • Fields are → MD5sum:Filesize:Comment

Whitelisting a signature should be performed with caution, as it has the potential to ignore legitimate virus's.

To whitelist a signature and add the signature name:

• Edit the signature white list file

  vim /var/lib/clamav/whitelist-signatures.ign2
   
  Signature.Ignore-1