Difference between revisions of "ClamAV"

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[[Category:Security]]
 
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[[zh-hans:ClamAV]]
[http://www.clamav.net Clam AntiVirus] is an open source (GPL) anti-virus toolkit for UNIX.  It provides a number of utilities including a flexible and scalable multi-threaded daemon, a command line scanner and advanced tool for automatic database updates. Because ClamAV's main use is on file/mail servers for Windows desktops it primarily detects Windows viruses and malware.
+
[https://www.clamav.net Clam AntiVirus] is an open source (GPL) anti-virus toolkit for UNIX.  It provides a number of utilities including a flexible and scalable multi-threaded daemon, a command line scanner and advanced tool for automatic database updates. Because ClamAV's main use is on file/mail servers for Windows desktops, it primarily detects Windows viruses and malware with its built-in signatures.
  
 
== Installation ==
 
== Installation ==
ClamAV can be [[pacman|installed]] with package {{Pkg|clamav}}, available in the [[Official Repositories]].
 
  
== Configuration ==
+
[[Install]] the {{Pkg|clamav}} package.
Whether you are going to use clamav as a daemon or use it as a simple file checker you need to comment out the line that contains the word ''Example'', usually it is found at the beginning of {{ic|/etc/clamav/freshclam.conf}} and {{ic|/etc/clamav/clamd.conf}} files.
 
 
 
== Starting the daemon ==
 
The service is called {{ic|clamd.service}}. Read [[Daemons]] for more information about starting it and enabling it to start at boot.
 
 
 
Also change the start options from "no" to "yes":
 
 
 
{{hc|/etc/conf.d/clamav|<nowiki>
 
# change these to "yes" to start
 
START_FRESHCLAM="yes"
 
START_CLAMD="yes"
 
</nowiki>}}
 
  
 
== Updating database ==
 
== Updating database ==
Edit the below file and comment out the line saying "Example"
 
{{hc|/etc/clamav/freshclam.conf|
 
# Comment or remove the line below.
 
# Example
 
}}
 
  
 
Update the virus definitions with:
 
Update the virus definitions with:
 +
 
  # freshclam
 
  # freshclam
  
 
The database files are saved in:
 
The database files are saved in:
 +
 
  /var/lib/clamav/daily.cvd
 
  /var/lib/clamav/daily.cvd
 
  /var/lib/clamav/main.cvd
 
  /var/lib/clamav/main.cvd
 +
/var/lib/clamav/bytecode.cvd
 +
 +
[[Start/enable]] {{ic|clamav-freshclam.service}} so that the virus definitions are kept recent.
 +
 +
== Starting the daemon ==
 +
 +
{{Note|You will need to run {{ic|freshclam}} before starting the service for the first time or you will run into troubles/errors which will prevent ClamAV to start correctly.}}
 +
 +
The service is called {{ic|clamav-daemon.service}}. [[Start]] it and [[enable]] it to start at boot.
 +
 +
== Testing the software ==
 +
 +
In order to make sure ClamAV and the definitions are installed correctly, scan the [https://www.eicar.org/86-0-Intended-use.html EICAR test file] (a harmless signature with no virus code) with clamscan.
 +
 +
$ curl https://www.eicar.org/download/eicar.com.txt | clamscan -
 +
 +
The output '''must''' include:
 +
 +
stdin: Eicar-Test-Signature FOUND
 +
 +
Otherwise; read the Troubleshooting part or ask for help in the [https://bbs.archlinux.org/ Arch Forums].
 +
 +
== Adding more databases/signatures repositories ==
 +
 +
ClamAV can use databases/signature from other repositories or security vendors.
 +
 +
To add the most important ones in a single step, install {{AUR|clamav-unofficial-sigs}}.
 +
 +
This will add signatures/databases from e.g. MalwarePatrol, SecuriteInfo, Yara, Linux Malware Detect, etc. For the full list of databases, [https://github.com/extremeshok/clamav-unofficial-sigs#description see the description of the GitHub repository].
 +
 +
=== Set up clamav-unofficial-sigs ===
 +
 +
[[Enable]] the {{ic|clamav-unofficial-sigs.timer}}.
 +
 +
This will regularly update the unofficial signatures based on the configuration files in the directory {{ic|/etc/clamav-unofficial-sigs}}.
 +
 +
To update signatures manually, run the following:
 +
 +
# clamav-unofficial-sigs.sh
 +
 +
To change any default settings, refer and modify {{ic|/etc/clamav-unofficial-sigs/user.conf}}.
 +
 +
{{Note|You still must have the {{ic|clamav-freshclam.service}} [[started]] in order to have official signature updates from ClamAV mirrors.}}
 +
 +
==== MalwarePatrol database ====
 +
 +
If you would like to use the MalwarePatrol database, sign up for an account at https://www.malwarepatrol.net/.
 +
 +
In {{ic|/etc/clamav-unofficial-sigs/user.conf}}, change the following to enable this functionality:
 +
 +
malwarepatrol_receipt_code="YOUR-RECEIPT-NUMBER" # enter your receipt number here
 +
malwarepatrol_product_code="8" # Use 8 if you have a Free account or 15 if you are a Premium customer.
 +
malwarepatrol_list="clamav_basic" # clamav_basic or clamav_ext
 +
malwarepatrol_free="yes" # Set to yes if you have a Free account or no if you are a Premium customer.
 +
 +
Source: https://www.malwarepatrol.net/clamav-configuration-guide/
 +
 +
== Scan for viruses ==
  
== Scan for Viruses ==
+
{{ic|clamscan}} can be used to scan certain files, home directories, or an entire system:
{{ic|clamscan}} can be used to scan certain files, home directory, or an entire system:
 
  
 
  $ clamscan myfile
 
  $ clamscan myfile
  $ clamscan -r -i /home
+
  $ clamscan --recursive --infected /home # or -r -i
  $ clamscan -r -i --exclude-dir='^/sys|^/proc|^/dev|^/lib|^/bin|^/sbin' /
+
  $ clamscan --recursive --infected --exclude-dir='^/sys|^/dev' /
 +
 
 +
If you would like {{ic|clamscan}} to remove the infected file add to the command the {{ic|--remove}} option, or you can use {{ic|1=--move=/dir}} to quarantine them.
  
If you would like {{ic|clamscan}} to remove the infected file use the {{ic|--remove}} option in the command.
+
You may also want {{ic|clamscan}} to scan larger files. In this case, append the options {{ic|1=--max-filesize=4000M}} and {{ic|1=--max-scansize=4000M}} to the command. '4000M' is the largest possible value, and may be lowered as necessary.
  
Using the {{ic|-l <path to file>}} option will print the {{ic|clamscan}} logs to a text  file for locating reported infections.
+
Using the {{ic|1=-l /path/to/file}} option will print the {{ic|clamscan}} logs to a text  file for locating reported infections.
 +
 
 +
== Using the milter ==
 +
 
 +
Milter will scan your sendmail server for email containing virus.
 +
Copy {{ic|/etc/clamav/clamav-milter.conf.sample}} to {{ic|/etc/clamav/clamav-milter.conf}} and adjust it to your needs. For example:
 +
 +
{{hc|/etc/clamav/clamav-milter.conf|2=
 +
MilterSocket /run/clamav/clamav-milter.sock
 +
MilterSocketMode 660
 +
FixStaleSocket yes
 +
User clamav
 +
PidFile /run/clamav/clamav-milter.pid
 +
TemporaryDirectory /tmp
 +
ClamdSocket unix:/var/lib/clamav/clamd.sock
 +
LogSyslog yes
 +
LogInfected Basic
 +
}}
 +
 
 +
Create {{ic|/etc/systemd/system/clamav-milter.service}}:
 +
 
 +
{{hc|/etc/systemd/system/clamav-milter.service|2=
 +
[Unit]
 +
Description='ClamAV Milter'
 +
After=clamav-daemon.service
 +
 
 +
[Service]
 +
Type=forking
 +
ExecStart=/usr/bin/clamav-milter --config-file /etc/clamav/clamav-milter.conf
 +
 
 +
[Install]
 +
WantedBy=multi-user.target
 +
}}
 +
 
 +
[[Enable]] and [[start]] {{ic|clamav-milter.service}}.
 +
 
 +
== OnAccessScan ==
 +
 
 +
On-access scanning requires the kernel to be compiled with the ''fanotify'' kernel module (kernel >= 3.8). Check if ''fanotify'' has been enabled before enabling on-access scanning.
 +
 
 +
$ zgrep FANOTIFY /proc/config.gz
 +
 
 +
On-access scanning will scan the file while reading, writing or executing it.
 +
 
 +
First, edit the {{ic|/etc/clamav/clamd.conf}} configuration file by adding the following to the end of the file (you can also change the individual options):
 +
 
 +
{{hc|/etc/clamav/clamd.conf|
 +
# Enables on-access scan, requires clamav-daemon.service running
 +
ScanOnAccess true
 +
 
 +
# Set the mount point where to recursively perform the scan,
 +
# this could be every path or multiple path (one line for path)
 +
OnAccessMountPath /usr
 +
OnAccessMountPath /home/
 +
OnAccessExcludePath /var/log/
 +
 
 +
# Flag fanotify to block any events on monitored files to perform the scan
 +
OnAccessPrevention false
 +
 
 +
# Perform scans on newly created, moved, or renamed files
 +
OnAccessExtraScanning true
 +
 
 +
# Check the UID from the event of fanotify
 +
OnAccessExcludeUID 0
 +
 
 +
# Specify an action to perform when clamav detects a malicious file
 +
# it is possible to specify an inline command too
 +
VirusEvent /etc/clamav/detected.sh
 +
 
 +
# WARNING: clamd should run as root
 +
User root
 +
}}
 +
 
 +
Next, create the file {{ic|/etc/clamav/detected.sh}} and add the following. This allows you to change/specify the debug message when a virus has been detected by clamd's on-access scanning service:
 +
 
 +
{{hc|/etc/clamav/detected.sh|2=<nowiki>
 +
#!/bin/bash
 +
PATH=/usr/bin
 +
 
 +
alert="Signature detected: $CLAM_VIRUSEVENT_VIRUSNAME in $CLAM_VIRUSEVENT_FILENAME"
 +
 
 +
# Send the alert to systemd logger if exist, othewise to /var/log
 +
if [[ -z $(command -v systemd-cat) ]]; then
 +
echo "$(date) - $alert" >> /var/log/clamav/infected.log
 +
else
 +
# as "emerg", this could cause your DE to show a visual alert. Happen in Plasma. but the next visual alert is much nicer
 +
echo "$alert" | /usr/bin/systemd-cat -t clamav -p emerg
 +
fi
 +
 
 +
#send an alrt to all graphical user
 +
XUSERS=($(who|awk '{print $1$NF}'|sort -u))
 +
 
 +
for XUSER in $XUSERS; do
 +
    NAME=(${XUSER/(/ })
 +
    DISPLAY=${NAME[1]/)/}
 +
    DBUS_ADDRESS=unix:path=/run/user/$(id -u ${NAME[0]})/bus
 +
    echo "run $NAME - $DISPLAY - $DBUS_ADDRESS -" >> /tmp/testlog
 +
    /usr/bin/sudo -u ${NAME[0]} DISPLAY=${DISPLAY} \
 +
                      DBUS_SESSION_BUS_ADDRESS=${DBUS_ADDRESS} \
 +
                      PATH=${PATH} \
 +
                      /usr/bin/notify-send -i dialog-warning "clamAV" "$alert"
 +
done
 +
</nowiki>}}
 +
 
 +
If you are using [[AppArmor]], it is also necessary to allow clamd to run as root:
 +
 
 +
# aa-complain clamd
 +
 
 +
[[Restart]] the {{ic|clamav-daemon.service}}.
 +
 
 +
Source: http://blog.clamav.net/2016/03/configuring-on-access-scanning-in-clamav.html
  
 
== Troubleshooting ==
 
== Troubleshooting ==
 +
 
=== Error: Clamd was NOT notified ===
 
=== Error: Clamd was NOT notified ===
 +
 
If you get the following messages after running freshclam:
 
If you get the following messages after running freshclam:
 +
 
{{bc|
 
{{bc|
 
WARNING: Clamd was NOT notified: Cannot connect to clamd through  
 
WARNING: Clamd was NOT notified: Cannot connect to clamd through  
Line 57: Line 217:
 
}}
 
}}
  
Add a sock file for clamav:
+
Add a sock file for ClamAV:
{{bc|
+
 
# touch /var/lib/clamav/clamd.sock
+
# touch /var/lib/clamav/clamd.sock
# chown clamav:clamav /var/lib/clamav/clamd.sock
+
# chown clamav:clamav /var/lib/clamav/clamd.sock
}}
+
 
Then, edit {{Ic|/etc/clamav/clamd.conf}} &ndash; uncomment this line:
+
Then, edit {{Ic|/etc/clamav/clamd.conf}} - uncomment this line:
{{bc|LocalSocket /var/lib/clamav/clamd.sock}}
+
 
Save the file and [[Daemons|restart the daemon]]
+
LocalSocket /var/lib/clamav/clamd.sock
 +
 
 +
Save the file and [[restart]] {{ic|clamav-daemon.service}}.
  
 
=== Error: No supported database files found ===
 
=== Error: No supported database files found ===
 +
 
If you get the next error when starting the daemon:
 
If you get the next error when starting the daemon:
 +
 
{{bc|
 
{{bc|
 
LibClamAV Error: cli_loaddb(): No supported database files found
 
LibClamAV Error: cli_loaddb(): No supported database files found
Line 73: Line 237:
 
}}
 
}}
 
   
 
   
Run freshclam as root:
+
This happens because of mismatch between {{ic|/etc/clamav/freshclam.conf}} setting {{ic|DatabaseDirectory}} and {{ic|/etc/clamav/clamd.conf}} setting {{ic|DatabaseDirectory}}.
{{bc|# freshclam -v}}
+
{{ic|/etc/clamav/freshclam.conf}} pointing to {{ic|/var/lib/clamav}}, but {{ic|/etc/clamav/clamd.conf}} (default directory) pointing to {{ic|/usr/share/clamav}}, or other directory. Edit in {{ic|/etc/clamav/clamd.conf}} and replace with the same DatabaseDirectory like in {{ic|/etc/clamav/freshclam.conf}}. After that clamav will start up successfully.
  
 
=== Error: Can't create temporary directory ===
 
=== Error: Can't create temporary directory ===
 +
 
If you get the following error, along with a 'HINT' containing a UID and a GID number:
 
If you get the following error, along with a 'HINT' containing a UID and a GID number:
{{bc|# can't create temporary directory}}
 
  
Do the following:
+
# can't create temporary directory
{{bc|# chown UID:GID /var/lib/clamav & chmod 755 /var/lib/clamav}}
+
 
 +
Correct permissions:
 +
 
 +
# chown UID:GID /var/lib/clamav & chmod 755 /var/lib/clamav
 +
 
 +
== See also ==
 +
 
 +
* [[Wikipedia:ClamAV]]
 +
* [[ClamSMTP]]

Latest revision as of 22:39, 19 June 2018

Clam AntiVirus is an open source (GPL) anti-virus toolkit for UNIX. It provides a number of utilities including a flexible and scalable multi-threaded daemon, a command line scanner and advanced tool for automatic database updates. Because ClamAV's main use is on file/mail servers for Windows desktops, it primarily detects Windows viruses and malware with its built-in signatures.

Installation

Install the clamav package.

Updating database

Update the virus definitions with:

# freshclam

The database files are saved in:

/var/lib/clamav/daily.cvd
/var/lib/clamav/main.cvd
/var/lib/clamav/bytecode.cvd

Start/enable clamav-freshclam.service so that the virus definitions are kept recent.

Starting the daemon

Note: You will need to run freshclam before starting the service for the first time or you will run into troubles/errors which will prevent ClamAV to start correctly.

The service is called clamav-daemon.service. Start it and enable it to start at boot.

Testing the software

In order to make sure ClamAV and the definitions are installed correctly, scan the EICAR test file (a harmless signature with no virus code) with clamscan.

$ curl https://www.eicar.org/download/eicar.com.txt | clamscan -

The output must include:

stdin: Eicar-Test-Signature FOUND

Otherwise; read the Troubleshooting part or ask for help in the Arch Forums.

Adding more databases/signatures repositories

ClamAV can use databases/signature from other repositories or security vendors.

To add the most important ones in a single step, install clamav-unofficial-sigsAUR.

This will add signatures/databases from e.g. MalwarePatrol, SecuriteInfo, Yara, Linux Malware Detect, etc. For the full list of databases, see the description of the GitHub repository.

Set up clamav-unofficial-sigs

Enable the clamav-unofficial-sigs.timer.

This will regularly update the unofficial signatures based on the configuration files in the directory /etc/clamav-unofficial-sigs.

To update signatures manually, run the following:

# clamav-unofficial-sigs.sh

To change any default settings, refer and modify /etc/clamav-unofficial-sigs/user.conf.

Note: You still must have the clamav-freshclam.service started in order to have official signature updates from ClamAV mirrors.

MalwarePatrol database

If you would like to use the MalwarePatrol database, sign up for an account at https://www.malwarepatrol.net/.

In /etc/clamav-unofficial-sigs/user.conf, change the following to enable this functionality:

malwarepatrol_receipt_code="YOUR-RECEIPT-NUMBER" # enter your receipt number here
malwarepatrol_product_code="8" # Use 8 if you have a Free account or 15 if you are a Premium customer.
malwarepatrol_list="clamav_basic" # clamav_basic or clamav_ext
malwarepatrol_free="yes" # Set to yes if you have a Free account or no if you are a Premium customer.

Source: https://www.malwarepatrol.net/clamav-configuration-guide/

Scan for viruses

clamscan can be used to scan certain files, home directories, or an entire system:

$ clamscan myfile
$ clamscan --recursive --infected /home # or -r -i
$ clamscan --recursive --infected --exclude-dir='^/sys|^/dev' /

If you would like clamscan to remove the infected file add to the command the --remove option, or you can use --move=/dir to quarantine them.

You may also want clamscan to scan larger files. In this case, append the options --max-filesize=4000M and --max-scansize=4000M to the command. '4000M' is the largest possible value, and may be lowered as necessary.

Using the -l /path/to/file option will print the clamscan logs to a text file for locating reported infections.

Using the milter

Milter will scan your sendmail server for email containing virus. Copy /etc/clamav/clamav-milter.conf.sample to /etc/clamav/clamav-milter.conf and adjust it to your needs. For example:

/etc/clamav/clamav-milter.conf
MilterSocket /run/clamav/clamav-milter.sock
MilterSocketMode 660
FixStaleSocket yes
User clamav
PidFile /run/clamav/clamav-milter.pid
TemporaryDirectory /tmp
ClamdSocket unix:/var/lib/clamav/clamd.sock
LogSyslog yes
LogInfected Basic

Create /etc/systemd/system/clamav-milter.service:

/etc/systemd/system/clamav-milter.service
[Unit]
Description='ClamAV Milter'
After=clamav-daemon.service

[Service]
Type=forking
ExecStart=/usr/bin/clamav-milter --config-file /etc/clamav/clamav-milter.conf

[Install]
WantedBy=multi-user.target

Enable and start clamav-milter.service.

OnAccessScan

On-access scanning requires the kernel to be compiled with the fanotify kernel module (kernel >= 3.8). Check if fanotify has been enabled before enabling on-access scanning.

$ zgrep FANOTIFY /proc/config.gz

On-access scanning will scan the file while reading, writing or executing it.

First, edit the /etc/clamav/clamd.conf configuration file by adding the following to the end of the file (you can also change the individual options):

/etc/clamav/clamd.conf
# Enables on-access scan, requires clamav-daemon.service running
ScanOnAccess true

# Set the mount point where to recursively perform the scan,
# this could be every path or multiple path (one line for path)
OnAccessMountPath /usr
OnAccessMountPath /home/
OnAccessExcludePath /var/log/

# Flag fanotify to block any events on monitored files to perform the scan
OnAccessPrevention false

# Perform scans on newly created, moved, or renamed files
OnAccessExtraScanning true

# Check the UID from the event of fanotify
OnAccessExcludeUID 0

# Specify an action to perform when clamav detects a malicious file
# it is possible to specify an inline command too
VirusEvent /etc/clamav/detected.sh

# WARNING: clamd should run as root
User root

Next, create the file /etc/clamav/detected.sh and add the following. This allows you to change/specify the debug message when a virus has been detected by clamd's on-access scanning service:

/etc/clamav/detected.sh
#!/bin/bash
PATH=/usr/bin

alert="Signature detected: $CLAM_VIRUSEVENT_VIRUSNAME in $CLAM_VIRUSEVENT_FILENAME"

# Send the alert to systemd logger if exist, othewise to /var/log
if [[ -z $(command -v systemd-cat) ]]; then
	echo "$(date) - $alert" >> /var/log/clamav/infected.log
else
	# as "emerg", this could cause your DE to show a visual alert. Happen in Plasma. but the next visual alert is much nicer
	echo "$alert" | /usr/bin/systemd-cat -t clamav -p emerg
fi

#send an alrt to all graphical user
XUSERS=($(who|awk '{print $1$NF}'|sort -u))

for XUSER in $XUSERS; do
    NAME=(${XUSER/(/ })
    DISPLAY=${NAME[1]/)/}
    DBUS_ADDRESS=unix:path=/run/user/$(id -u ${NAME[0]})/bus
    echo "run $NAME - $DISPLAY - $DBUS_ADDRESS -" >> /tmp/testlog 
    /usr/bin/sudo -u ${NAME[0]} DISPLAY=${DISPLAY} \
                       DBUS_SESSION_BUS_ADDRESS=${DBUS_ADDRESS} \
                       PATH=${PATH} \
                       /usr/bin/notify-send -i dialog-warning "clamAV" "$alert"
done

If you are using AppArmor, it is also necessary to allow clamd to run as root:

# aa-complain clamd

Restart the clamav-daemon.service.

Source: http://blog.clamav.net/2016/03/configuring-on-access-scanning-in-clamav.html

Troubleshooting

Error: Clamd was NOT notified

If you get the following messages after running freshclam:

WARNING: Clamd was NOT notified: Cannot connect to clamd through 
/var/lib/clamav/clamd.sock connect(): No such file or directory

Add a sock file for ClamAV:

# touch /var/lib/clamav/clamd.sock
# chown clamav:clamav /var/lib/clamav/clamd.sock

Then, edit /etc/clamav/clamd.conf - uncomment this line:

LocalSocket /var/lib/clamav/clamd.sock

Save the file and restart clamav-daemon.service.

Error: No supported database files found

If you get the next error when starting the daemon:

LibClamAV Error: cli_loaddb(): No supported database files found
in /var/lib/clamav ERROR: Not supported data format

This happens because of mismatch between /etc/clamav/freshclam.conf setting DatabaseDirectory and /etc/clamav/clamd.conf setting DatabaseDirectory. /etc/clamav/freshclam.conf pointing to /var/lib/clamav, but /etc/clamav/clamd.conf (default directory) pointing to /usr/share/clamav, or other directory. Edit in /etc/clamav/clamd.conf and replace with the same DatabaseDirectory like in /etc/clamav/freshclam.conf. After that clamav will start up successfully.

Error: Can't create temporary directory

If you get the following error, along with a 'HINT' containing a UID and a GID number:

# can't create temporary directory

Correct permissions:

# chown UID:GID /var/lib/clamav & chmod 755 /var/lib/clamav

See also